Very Rough IDLE .. HELP!!! - 1991 Mazda MPV, 4 cyl.

BlankI have a 1991 Mazda MPV - 4 cyl 2.6L eng., manual trans, with
240,000km/140,000 mi. It has served me very well over the yrs and I have had
no real complaints with it until recently. About 6 months ago, it started
developing a rough idle after warmup(idles fine when engine cold). This has
become gradually worse, ...now idles very rough at around 500 RPM .. almost
to the point of stalling.

Here's what I've checked so far:
Wires - Recently replaced but checked anyway ... consistent rhythmic blue
sparks on all four
Plugs- Normal
Air FIlter - Replaced
Rotor/Cap - Replaced
O2 Sensor - Replaced
PCV Valve - Replaced
Air Flow Meter - Checks out, all votages within spec
Idle Speed Control - Resistance within Specs
Throttle Pos Sensor - Voltage within Specs
Water Temp Sensor - Within spec
Intake Air Tem Sensor - Within Spec
Soleniod valve controlling Fuel Pressure Regualtor - checks out fine

With above checks complete my attention turned to looking for either a fuel
supply problem (including bad injectors), or a vacuum leak ( unmetered air
entering intake manifold)
Fuel Supply.... Seeing that engine runs fine at cold idle , I suspect
problem is not likely with fuel delivery. Just to be sure though, I did
check each injector for proper operation using a makeshift stetescope (screw
driver tip on injector, ear on other end). All injectors seem to be working
fine in that I could hear each of them rhythmicaly clicking away. I did not
go as far as checking the fuel pressure (do not have the right tools). But
seeing that cold Idle is fine, and engine can rev high without hesitation, I
didn't see any point in checking.... Should I?
Vacuum leak. Checked all vacuum hoses coming out of intake manifold. Pinched
each one with no noticeable difference in Idle. I'm a little embarrassed to
admit this part for obvious reasons...., but I also used a small propane
tank (of the plumbing welding variety) and probed along all vacuum lines and
all around the intake manifold..... I detected no change in idle speed at
all.

One final check .. the EFI self disgnostics... No codes stored.. which makes
sense since engine warning light does not come on.

At this point .. I'm runing out of ideas and would appreciate any
suggestions out there. Needless to say, I'd rather not take it to the dealer
and risk getting soaked for unnecessary expensive repairs.

Thanks in advance for your responses!

Regards

Terry

Toronto(Brampton), Ontario, Canada

Hi Terry,

How about the EGR system? I didn't see it listed. Maybe the symptoms
you describe appear because the idle air input is being controlled by
an air inlet solenoid when the engine is cold for a fast idle, which
would shut off when the engine warmed up. Rough idle when warm could
be a symptom of a bad EGR valve, solenoid or somesuch related
component in the EGR system, where exhaust gasses are being introduced
to the intake air at idle (which I think should only occur under load
when warm).

Just a theory, worth checking out.

Matt

"Terry St.Laurent" <(E-Mail Removed)> wrote in message news:<aKmdnY72mNzTkhzcRVn-(E-Mail Removed)>...
> BlankI have a 1991 Mazda MPV - 4 cyl 2.6L eng., manual trans, with
> 240,000km/140,000 mi. It has served me very well over the yrs and I have had
> no real complaints with it until recently. About 6 months ago, it started
> developing a rough idle after warmup(idles fine when engine cold). This has
> become gradually worse, ...now idles very rough at around 500 RPM .. almost
> to the point of stalling.
>
> Here's what I've checked so far:
> Wires - Recently replaced but checked anyway ... consistent rhythmic blue
> sparks on all four
> Plugs- Normal
> Air FIlter - Replaced
> Rotor/Cap - Replaced
> O2 Sensor - Replaced
> PCV Valve - Replaced
> Air Flow Meter - Checks out, all votages within spec
> Idle Speed Control - Resistance within Specs
> Throttle Pos Sensor - Voltage within Specs
> Water Temp Sensor - Within spec
> Intake Air Tem Sensor - Within Spec
> Soleniod valve controlling Fuel Pressure Regualtor - checks out fine
>
> With above checks complete my attention turned to looking for either a fuel
> supply problem (including bad injectors), or a vacuum leak ( unmetered air
> entering intake manifold)
> Fuel Supply.... Seeing that engine runs fine at cold idle , I suspect
> problem is not likely with fuel delivery. Just to be sure though, I did
> check each injector for proper operation using a makeshift stetescope (screw
> driver tip on injector, ear on other end). All injectors seem to be working
> fine in that I could hear each of them rhythmicaly clicking away. I did not
> go as far as checking the fuel pressure (do not have the right tools). But
> seeing that cold Idle is fine, and engine can rev high without hesitation, I
> didn't see any point in checking.... Should I?
> Vacuum leak. Checked all vacuum hoses coming out of intake manifold. Pinched
> each one with no noticeable difference in Idle. I'm a little embarrassed to
> admit this part for obvious reasons...., but I also used a small propane
> tank (of the plumbing welding variety) and probed along all vacuum lines and
> all around the intake manifold..... I detected no change in idle speed at
> all.
>
> One final check .. the EFI self disgnostics... No codes stored.. which makes
> sense since engine warning light does not come on.
>
> At this point .. I'm runing out of ideas and would appreciate any
> suggestions out there. Needless to say, I'd rather not take it to the dealer
> and risk getting soaked for unnecessary expensive repairs.
>
> Thanks in advance for your responses!
>
> Regards
>
> Terry
>
> Toronto(Brampton), Ontario, Canada

Might be wrong.. but I think this engine uses a different type of system ...
the IdleSpeedControl(ISC) which adjust idle air intake based on coolant
temp...
"Matt" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
> Hi Terry,
>
> How about the EGR system? I didn't see it listed. Maybe the symptoms
> you describe appear because the idle air input is being controlled by
> an air inlet solenoid when the engine is cold for a fast idle, which
> would shut off when the engine warmed up. Rough idle when warm could
> be a symptom of a bad EGR valve, solenoid or somesuch related
> component in the EGR system, where exhaust gasses are being introduced
> to the intake air at idle (which I think should only occur under load
> when warm).
>
> Just a theory, worth checking out.
>
> Matt
>
> "Terry St.Laurent" <(E-Mail Removed)> wrote in message
news:<aKmdnY72mNzTkhzcRVn-(E-Mail Removed)>...
> > BlankI have a 1991 Mazda MPV - 4 cyl 2.6L eng., manual trans, with
> > 240,000km/140,000 mi. It has served me very well over the yrs and I have
had
> > no real complaints with it until recently. About 6 months ago, it
started
> > developing a rough idle after warmup(idles fine when engine cold). This
has
> > become gradually worse, ...now idles very rough at around 500 RPM ..
almost
> > to the point of stalling.
> >
> > Here's what I've checked so far:
> > Wires - Recently replaced but checked anyway ... consistent rhythmic
blue
> > sparks on all four
> > Plugs- Normal
> > Air FIlter - Replaced
> > Rotor/Cap - Replaced
> > O2 Sensor - Replaced
> > PCV Valve - Replaced
> > Air Flow Meter - Checks out, all votages within spec
> > Idle Speed Control - Resistance within Specs
> > Throttle Pos Sensor - Voltage within Specs
> > Water Temp Sensor - Within spec
> > Intake Air Tem Sensor - Within Spec
> > Soleniod valve controlling Fuel Pressure Regualtor - checks out fine
> >
> > With above checks complete my attention turned to looking for either a
fuel
> > supply problem (including bad injectors), or a vacuum leak ( unmetered
air
> > entering intake manifold)
> > Fuel Supply.... Seeing that engine runs fine at cold idle , I suspect
> > problem is not likely with fuel delivery. Just to be sure though, I did
> > check each injector for proper operation using a makeshift stetescope
(screw
> > driver tip on injector, ear on other end). All injectors seem to be
working
> > fine in that I could hear each of them rhythmicaly clicking away. I did
not
> > go as far as checking the fuel pressure (do not have the right tools).
But
> > seeing that cold Idle is fine, and engine can rev high without
hesitation, I
> > didn't see any point in checking.... Should I?
> > Vacuum leak. Checked all vacuum hoses coming out of intake manifold.
Pinched
> > each one with no noticeable difference in Idle. I'm a little embarrassed
to
> > admit this part for obvious reasons...., but I also used a small propane
> > tank (of the plumbing welding variety) and probed along all vacuum lines
and
> > all around the intake manifold..... I detected no change in idle speed
at
> > all.
> >
> > One final check .. the EFI self disgnostics... No codes stored.. which
makes
> > sense since engine warning light does not come on.
> >
> > At this point .. I'm runing out of ideas and would appreciate any
> > suggestions out there. Needless to say, I'd rather not take it to the
dealer
> > and risk getting soaked for unnecessary expensive repairs.
> >
> > Thanks in advance for your responses!
> >
> > Regards
> >
> > Terry
> >
> > Toronto(Brampton), Ontario, Canada

If you are at 500 rpm while hot it is too low usually 4 cylinders run
around 700 to 1000 rpm hot idle. So this suggests insufficient air
flow. One thing common is throttle body near throttle plate gets
gunked up with carbon. Try disconnecting rubber boot near throttle
plate. If you have a Map sensor you can get engine running and hold
near 2000 rpm and have helper pulse spray carburetor cleaner around
throttle plate especially into idle air inlet hole before throttle
plate to get it clear. If you have a MAF sensor you usually can't
keep engine running with rubber hose off so try pulling off a hose in
rubber duct and with a straw on carb can and a rag around it to seal
air leak a bit have helper spray into duct as you open and close
throttle.
If you can't keep car running disconnect rubber duct spray
liberally with carb cleaner around throttle plate and idle air hole,
reconnect duct, start engine and rev for a couple minutes, turn engine
off and repeat process a few times.
Otherwise it could be coolant temperature. but you said you
checked it already. It could also be defective IAC idle air control
valve that computer uses to control air flow around throttle plate.

"Terry St.Laurent" <(E-Mail Removed)> wrote in message news:<TOidncjGU_FMJR_cRVn-(E-Mail Removed)>...
> Might be wrong.. but I think this engine uses a different type of system ...
> the IdleSpeedControl(ISC) which adjust idle air intake based on coolant
> temp...
> "Matt" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed) om...
> > Hi Terry,
> >
> > How about the EGR system? I didn't see it listed. Maybe the symptoms
> > you describe appear because the idle air input is being controlled by
> > an air inlet solenoid when the engine is cold for a fast idle, which
> > would shut off when the engine warmed up. Rough idle when warm could
> > be a symptom of a bad EGR valve, solenoid or somesuch related
> > component in the EGR system, where exhaust gasses are being introduced
> > to the intake air at idle (which I think should only occur under load
> > when warm).
> >
> > Just a theory, worth checking out.
> >
> > Matt
> >
> > "Terry St.Laurent" <(E-Mail Removed)> wrote in message
> news:<aKmdnY72mNzTkhzcRVn-(E-Mail Removed)>...
> > > BlankI have a 1991 Mazda MPV - 4 cyl 2.6L eng., manual trans, with
> > > 240,000km/140,000 mi. It has served me very well over the yrs and I have
> had
> > > no real complaints with it until recently. About 6 months ago, it
> started
> > > developing a rough idle after warmup(idles fine when engine cold). This
> has
> > > become gradually worse, ...now idles very rough at around 500 RPM ..
> almost
> > > to the point of stalling.
> > >
> > > Here's what I've checked so far:
> > > Wires - Recently replaced but checked anyway ... consistent rhythmic
> blue
> > > sparks on all four
> > > Plugs- Normal
> > > Air FIlter - Replaced
> > > Rotor/Cap - Replaced
> > > O2 Sensor - Replaced
> > > PCV Valve - Replaced
> > > Air Flow Meter - Checks out, all votages within spec
> > > Idle Speed Control - Resistance within Specs
> > > Throttle Pos Sensor - Voltage within Specs
> > > Water Temp Sensor - Within spec
> > > Intake Air Tem Sensor - Within Spec
> > > Soleniod valve controlling Fuel Pressure Regualtor - checks out fine
> > >
> > > With above checks complete my attention turned to looking for either a
> fuel
> > > supply problem (including bad injectors), or a vacuum leak ( unmetered
> air
> > > entering intake manifold)
> > > Fuel Supply.... Seeing that engine runs fine at cold idle , I suspect
> > > problem is not likely with fuel delivery. Just to be sure though, I did
> > > check each injector for proper operation using a makeshift stetescope
> (screw
> > > driver tip on injector, ear on other end). All injectors seem to be
> working
> > > fine in that I could hear each of them rhythmicaly clicking away. I did
> not
> > > go as far as checking the fuel pressure (do not have the right tools).
> But
> > > seeing that cold Idle is fine, and engine can rev high without
> hesitation, I
> > > didn't see any point in checking.... Should I?
> > > Vacuum leak. Checked all vacuum hoses coming out of intake manifold.
> Pinched
> > > each one with no noticeable difference in Idle. I'm a little embarrassed
> to
> > > admit this part for obvious reasons...., but I also used a small propane
> > > tank (of the plumbing welding variety) and probed along all vacuum lines
> and
> > > all around the intake manifold..... I detected no change in idle speed
> at
> > > all.
> > >
> > > One final check .. the EFI self disgnostics... No codes stored.. which
> makes
> > > sense since engine warning light does not come on.
> > >
> > > At this point .. I'm runing out of ideas and would appreciate any
> > > suggestions out there. Needless to say, I'd rather not take it to the
> dealer
> > > and risk getting soaked for unnecessary expensive repairs.
> > >
> > > Thanks in advance for your responses!
> > >
> > > Regards
> > >
> > > Terry
> > >
> > > Toronto(Brampton), Ontario, Canada

Just going on what I know, not really familiar with this engine, but
if this motor is anything like the early '90s escorts, take a look at
the large air intake tube from the air box to the throttle body, if
there is a large crack in it, you should be able to hold your hand
over the crack and see the idle speed increase. Happened once to
someone in my family, I put some duct tape on it until the part could
be replaced.

Matt

"Terry St.Laurent" <(E-Mail Removed)> wrote in message news:<TOidncjGU_FMJR_cRVn-(E-Mail Removed)>...
> Might be wrong.. but I think this engine uses a different type of system ...
> the IdleSpeedControl(ISC) which adjust idle air intake based on coolant
> temp...
> "Matt" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed) om...
> > Hi Terry,
> >
> > How about the EGR system? I didn't see it listed. Maybe the symptoms
> > you describe appear because the idle air input is being controlled by
> > an air inlet solenoid when the engine is cold for a fast idle, which
> > would shut off when the engine warmed up. Rough idle when warm could
> > be a symptom of a bad EGR valve, solenoid or somesuch related
> > component in the EGR system, where exhaust gasses are being introduced
> > to the intake air at idle (which I think should only occur under load
> > when warm).
> >
> > Just a theory, worth checking out.
> >
> > Matt
> >
> > "Terry St.Laurent" <(E-Mail Removed)> wrote in message
> news:<aKmdnY72mNzTkhzcRVn-(E-Mail Removed)>...
> > > BlankI have a 1991 Mazda MPV - 4 cyl 2.6L eng., manual trans, with
> > > 240,000km/140,000 mi. It has served me very well over the yrs and I have
> had
> > > no real complaints with it until recently. About 6 months ago, it
> started
> > > developing a rough idle after warmup(idles fine when engine cold). This
> has
> > > become gradually worse, ...now idles very rough at around 500 RPM ..
> almost
> > > to the point of stalling.
> > >
> > > Here's what I've checked so far:
> > > Wires - Recently replaced but checked anyway ... consistent rhythmic
> blue
> > > sparks on all four
> > > Plugs- Normal
> > > Air FIlter - Replaced
> > > Rotor/Cap - Replaced
> > > O2 Sensor - Replaced
> > > PCV Valve - Replaced
> > > Air Flow Meter - Checks out, all votages within spec
> > > Idle Speed Control - Resistance within Specs
> > > Throttle Pos Sensor - Voltage within Specs
> > > Water Temp Sensor - Within spec
> > > Intake Air Tem Sensor - Within Spec
> > > Soleniod valve controlling Fuel Pressure Regualtor - checks out fine
> > >
> > > With above checks complete my attention turned to looking for either a
> fuel
> > > supply problem (including bad injectors), or a vacuum leak ( unmetered
> air
> > > entering intake manifold)
> > > Fuel Supply.... Seeing that engine runs fine at cold idle , I suspect
> > > problem is not likely with fuel delivery. Just to be sure though, I did
> > > check each injector for proper operation using a makeshift stetescope
> (screw
> > > driver tip on injector, ear on other end). All injectors seem to be
> working
> > > fine in that I could hear each of them rhythmicaly clicking away. I did
> not
> > > go as far as checking the fuel pressure (do not have the right tools).
> But
> > > seeing that cold Idle is fine, and engine can rev high without
> hesitation, I
> > > didn't see any point in checking.... Should I?
> > > Vacuum leak. Checked all vacuum hoses coming out of intake manifold.
> Pinched
> > > each one with no noticeable difference in Idle. I'm a little embarrassed
> to
> > > admit this part for obvious reasons...., but I also used a small propane
> > > tank (of the plumbing welding variety) and probed along all vacuum lines
> and
> > > all around the intake manifold..... I detected no change in idle speed
> at
> > > all.
> > >
> > > One final check .. the EFI self disgnostics... No codes stored.. which
> makes
> > > sense since engine warning light does not come on.
> > >
> > > At this point .. I'm runing out of ideas and would appreciate any
> > > suggestions out there. Needless to say, I'd rather not take it to the
> dealer
> > > and risk getting soaked for unnecessary expensive repairs.
> > >
> > > Thanks in advance for your responses!
> > >
> > > Regards
> > >
> > > Terry
> > >
> > > Toronto(Brampton), Ontario, Canada

Timing belt?


"Terry St.Laurent" <(E-Mail Removed)> wrote in message
news:aKmdnY72mNzTkhzcRVn-(E-Mail Removed)...
> BlankI have a 1991 Mazda MPV - 4 cyl 2.6L eng., manual trans, with
> 240,000km/140,000 mi. It has served me very well over the yrs and I have
> had
> no real complaints with it until recently. About 6 months ago, it started
> developing a rough idle after warmup(idles fine when engine cold). This
> has
> become gradually worse, ...now idles very rough at around 500 RPM ..
> almost
> to the point of stalling.
>
> Here's what I've checked so far:
> Wires - Recently replaced but checked anyway ... consistent rhythmic blue
> sparks on all four
> Plugs- Normal
> Air FIlter - Replaced
> Rotor/Cap - Replaced
> O2 Sensor - Replaced
> PCV Valve - Replaced
> Air Flow Meter - Checks out, all votages within spec
> Idle Speed Control - Resistance within Specs
> Throttle Pos Sensor - Voltage within Specs
> Water Temp Sensor - Within spec
> Intake Air Tem Sensor - Within Spec
> Soleniod valve controlling Fuel Pressure Regualtor - checks out fine
>
> With above checks complete my attention turned to looking for either a
> fuel
> supply problem (including bad injectors), or a vacuum leak ( unmetered air
> entering intake manifold)
> Fuel Supply.... Seeing that engine runs fine at cold idle , I suspect
> problem is not likely with fuel delivery. Just to be sure though, I did
> check each injector for proper operation using a makeshift stetescope
> (screw
> driver tip on injector, ear on other end). All injectors seem to be
> working
> fine in that I could hear each of them rhythmicaly clicking away. I did
> not
> go as far as checking the fuel pressure (do not have the right tools). But
> seeing that cold Idle is fine, and engine can rev high without hesitation,
> I
> didn't see any point in checking.... Should I?
> Vacuum leak. Checked all vacuum hoses coming out of intake manifold.
> Pinched
> each one with no noticeable difference in Idle. I'm a little embarrassed
> to
> admit this part for obvious reasons...., but I also used a small propane
> tank (of the plumbing welding variety) and probed along all vacuum lines
> and
> all around the intake manifold..... I detected no change in idle speed at
> all.
>
> One final check .. the EFI self disgnostics... No codes stored.. which
> makes
> sense since engine warning light does not come on.
>
> At this point .. I'm runing out of ideas and would appreciate any
> suggestions out there. Needless to say, I'd rather not take it to the
> dealer
> and risk getting soaked for unnecessary expensive repairs.
>
> Thanks in advance for your responses!
>
> Regards
>
> Terry
>
> Toronto(Brampton), Ontario, Canada
>
>

If you just want to throw parts at it, replace the fuel filter. Throw in a
bottle of HEET while you're at it. BTW, the engine light coming on has little to
do with there being engine codes to check.

DWJ wrote:
>
> Timing belt?
>
> "Terry St.Laurent" <(E-Mail Removed)> wrote in message
> news:aKmdnY72mNzTkhzcRVn-(E-Mail Removed)...
> > BlankI have a 1991 Mazda MPV - 4 cyl 2.6L eng., manual trans, with
> > 240,000km/140,000 mi. It has served me very well over the yrs and I have
> > had
> > no real complaints with it until recently. About 6 months ago, it started
> > developing a rough idle after warmup(idles fine when engine cold). This
> > has
> > become gradually worse, ...now idles very rough at around 500 RPM ..
> > almost
> > to the point of stalling.
> >
> > Here's what I've checked so far:
> > Wires - Recently replaced but checked anyway ... consistent rhythmic blue
> > sparks on all four
> > Plugs- Normal
> > Air FIlter - Replaced
> > Rotor/Cap - Replaced
> > O2 Sensor - Replaced
> > PCV Valve - Replaced
> > Air Flow Meter - Checks out, all votages within spec
> > Idle Speed Control - Resistance within Specs
> > Throttle Pos Sensor - Voltage within Specs
> > Water Temp Sensor - Within spec
> > Intake Air Tem Sensor - Within Spec
> > Soleniod valve controlling Fuel Pressure Regualtor - checks out fine
> >
> > With above checks complete my attention turned to looking for either a
> > fuel
> > supply problem (including bad injectors), or a vacuum leak ( unmetered air
> > entering intake manifold)
> > Fuel Supply.... Seeing that engine runs fine at cold idle , I suspect
> > problem is not likely with fuel delivery. Just to be sure though, I did
> > check each injector for proper operation using a makeshift stetescope
> > (screw
> > driver tip on injector, ear on other end). All injectors seem to be
> > working
> > fine in that I could hear each of them rhythmicaly clicking away. I did
> > not
> > go as far as checking the fuel pressure (do not have the right tools). But
> > seeing that cold Idle is fine, and engine can rev high without hesitation,
> > I
> > didn't see any point in checking.... Should I?
> > Vacuum leak. Checked all vacuum hoses coming out of intake manifold.
> > Pinched
> > each one with no noticeable difference in Idle. I'm a little embarrassed
> > to
> > admit this part for obvious reasons...., but I also used a small propane
> > tank (of the plumbing welding variety) and probed along all vacuum lines
> > and
> > all around the intake manifold..... I detected no change in idle speed at
> > all.
> >
> > One final check .. the EFI self disgnostics... No codes stored.. which
> > makes
> > sense since engine warning light does not come on.
> >
> > At this point .. I'm runing out of ideas and would appreciate any
> > suggestions out there. Needless to say, I'd rather not take it to the
> > dealer
> > and risk getting soaked for unnecessary expensive repairs.
> >
> > Thanks in advance for your responses!
> >
> > Regards
> >
> > Terry
> >
> > Toronto(Brampton), Ontario, Canada
> >
> >