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

Sharon K.Cooke

2005-05-16 19:36:37 UTC

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.

Post by DWJ
Timing belt?

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.
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