91 grand prix

:banghead: i have a 91 grand prix 3.1,the problem is i while driving this car when i proceed to come of the gas the car seems to come down to idle then it seems to stall out,this problem happens intermittently,when this happens i turn the key off and the car starts up just fine. this is very nerve racking,the car has a new idle control valve and new plugs.any ideas what would be causing this? thanks

1st off, welcome to the forums. Is the "check engine" light on? Can you describe what the problem is again? jDoes it stall after you slow down to almost a stop? We need a little more info please.

when the rpms come down the car stalls out intermittently,service engine light does come on but when turn the ignition completely off the car starts right up.and the service light goes off,also the car is warmed up when this is happening,no code is stored

I assume the check engine light only comes on after the car stalls, not while it's running, correct?

yes you are correct

It sounds like a bad ECM to me if fuel pressure is good when it dies.. A bad ignition module or crank sensor will normally trip a CEL. If you lose injector pulse when the car dies, it's most likely a bad ECM. You can try a tap test on the ECM while the car is running, if tapping on the ECM causes the car to stumble or die, you found your problem. Make sure the harness isn't corroded before changing it, as it is mounted under the hood (in the passenger side fender well under a plastic cover) and exposed to the elements. I'd hate for you to buy and ECM only to find that the harness is corroded. Most (if not all) parts stores will not take an ECM back once the box has been opened or if the part was installed, so check the harness really good if it fails the "tap test". If the ECM passes the tap test, then you need to check fuel pressure. It should be 31-35psi key on, engine off, (any less and the fule pump is bad) and should drop 3-7 psi with the engine started and the vacuum line attached. Disconnecting the vacuum line while the engine is running should cause the fuel pressure to spike back up to near the key on engine off pressure. If not, the regulator is bad.

when you say tap on the ecm do mean with your hand or use a solid object

Use a screwdrver handle or soft faced hammer, but just tap, don't go beating on it.

JC, .. Have you resolved the problem on your '91? I have the same problem, exactly. I am starting to suspect the transmission is dragging when in overdrive somehow or the tranny speed sensors or gear sensors are not reporting correctly to the ECM or the ECM is faulty. The car runs perfectly after warm-up if I turn off the ignition and wait a few seconds then restart. I've replaced MAP, alternator, IAC motor (first). I'm finding a work-around by puting the car in 2nd gear to start off, then shifting into D but not using OD anymore. This has worked for 2 days of short trips now. What 'cha know???