Intermittent problem on my 1988 GT/5 speed that has become permanent. When the car is first started, it will run fine – the system is in open loop. But when the car heats up enough to go closed loop, the car won’t idle. The idle hunts between about 1500 RPM and close to stalling. This alternation between good idle and close to stalling occurs very rapidly – about two seconds per cycle. When the engine is near stall, the CHECK ENGINE LIGHT comes on briefly until the idle picks up again. If I can get the engine to run above about 2000 RPM then it runs fine, but it is sometimes very difficult to get the revs up because of the idle hunting. I checked the codes and none are set. My thought is that the speedometer buffer is not talking to the ECM. I checked the continuity between the speedometer buffer output (2000PPM square wave) and the ECM and it is good. I thought the connector on the buffer circuit board might be corroded, so I cleaned that and the contact on the circuit board. The problem persists. What else can it be??? Thanks
Check the timing, my timing was advanced way too much and my idle was like yours, I also cleaned the IAC valve now the idle is pretty level. Mine is a 2.5 but I think it still applies to the V6.
The plugs have less than 10K miles on them. Could you please explain how the engine would run fine in open loop mode (when cold), but not in closed loop mode if the problem is fuel pressure? I can't see how that would happen.
The plugs have less than 10K miles on them. Could you please explain how the engine would run fine in open loop mode (when cold), but not in closed loop mode if the problem is fuel pressure? I can't see how that would happen.
The ECM is programmed to provide additional fuel when cold. As the engine warms the ECM is programmed to provide less. Low fuel pressure might allow the engine to run reasonable when cold, but when warmed up and when ECM is cutting back on the fueling the engine combined with low fuel pressure that could then cause the engine to run so poor that it starts to stall and then the ECM opens the IAC more and the engine revs up, only to repeat. It's only a 'maybe' and checking the fuel pressure can either identify it as the cause or eliminate it as a suspect.
Do you have a scanner? Does this problem start and stop exactly when the vehicle goes into closed loop?
Have you tried disconnecting the O2 sensor and see if the problem persists. Disconnecting the O2 sensor will keep the engine in open loop operation.
GM limited the range that the ECM can alter the fueling based on the O2 sensor. So while the O2 sensor input to the ECM can fool the ECM into leaning out the engine it shouldn't be leaning it out to the point that the engine stalls or near-stalls.
Maybe try this? My car has anup and own idle once its warmed up but if its running in the driveway it'll get hot and not hunt for idle. I'm gonna investigate this this weekend on my car.
I think it's due to a dirty IAC. I'm going to remove,clean, and reinstall mine to see if it helps. I ave the same issues you do. If I let it warm in the driveway it idles just fine, but after coming off the highway, it's up and down dipping oil pressure into the red zone and back and forth.
Have you tried cleaning the IAC and IAC port already?
------------------ Louis Duet Baldwin, Long Island, NY "Blue" <= '85 Fiero GT Stock V6---Stock everything. ~~~~~~~~~~~~~~~~~~~~~ "Boo" <= '81 Delorean DMC-12 VIN #5835 Stock PRV engine Robertson Equipped Neiland/Delman Engineered Carbed and loving it! (Peugot 604 manifold) ---"Sorry purists"