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

[DWJ]

Timing belt?


"Terry St.Laurent" <tstlaur@rogers.com> wrote in message
news:aKmdnY72mNzTkhzcRVn-sA@rogers.com...
> 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
>
>

[Sharon K.Cooke]

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" <tstlaur@rogers.com> wrote in message
> news:aKmdnY72mNzTkhzcRVn-sA@rogers.com...
> > 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
> >
> >