Help. Engine has mind of its own.

Problem first manifest itself as engine quitting intermittently - but would restart. Problem became more frequent, then finally wouldn't start except infrequently. Would only start when cold, then run for awhile, then RPMs fluctuate even though the throttle is not being manipulated.

Initial troubleshooting
-----------------------------
Fuel pressure checks at 31 psi.
Replaced spark plugs, wires, dist. cap and rotor.
Replaced air filter and fuel filter.
Checked plugs for spark - checks OK.
No cracks in the air inlet duct (replaced recently).
No observable cracks or damage to vacuum hoses in the EFI or smog systems.

The weird engine RPM fluctuation led me to believe that the EFI control unit (computer) was hosed. Wrong. Swapped computer and no change (except to my bank account).

Any ideas?

Check your engine sensors. That usually ends up being the culprit in these cases. Or could be a solenoid. I wouldn't be able to give you more specific than that though. Hook it up to a computer and get a diagnostic.

Originally posted by DVSNCYNIKL
Check your engine sensors. That usually ends up being the culprit in these cases. Or could be a solenoid. I wouldn't be able to give you more specific than that though. Hook it up to a computer and get a diagnostic.

I second this. Get a diagnostic.Is your check engine light on? if so, did you try resetting the code(s)? Buy a cheap reader or borrow one if possible and find out what the codes are. This should give you a good indication of the problem.

Thanks for the response. Forgot to mention that at no time did I get a code from the computer or Check Engine light. I would like to get the thing hooked up to a diagnostic device, but need to get it mobile first.

My next action will be to remove and test all of the sensors. Was hoping someone has a notion from the info I have assembled, which one could cause these symptoms, so I'll know where to start - as opposed to the "poking and hoping" approach.

Could be an oxygen sensor.

Originally posted by DVSNCYNIKL
Could be an oxygen sensor.

Doubtful, if the O2 sensor failed the computer would just go to the limp-home mode and the car would start and run just there would be power loss, but there would be codes and a check engine light too.

As far as helping you get your car running Bosco, the last thing i can possibly think of is the connection to your maf is messed up, or the maf sensor itself? im just grasping at straws at this point...sorry dude

What Mazda engine is that?
It could be the EGR valve that is stuck open or partly open?
This would explain why the thing tends to start cold-when the mixture is richer.
Just a hunch. as we all know: could be anything.

Hang in there.
Len

Very possible you have a failing distributor. Electronic sensor tends to go bad and requires replacement. New distributor will run around $290, but you can get a rebuild with your trade in for about $180. I had the sae problem with intermittednt operation and random failure. I don't recall RPM wacking out, but then I was not looking for that

Other possibility is the fuel pump or the fuel pump relay.

Did you ever figure out what was wrong? My 94 626 quits but restarts about one to two minutes later if reved over 4000 for over 3-4 seconds.