I'm kinda getting tired of the MPFI swap car running goofy, so its time for a little research.
What tells the car to high idle a little upon startup? When the car was TBI, sometimes I would start it and it would not high idle and go right to 800 RPMs and run funny. Now that I swapped the MPFI on it, all the sensors are different, but it still pulls the same crap every now and then.
Is that in the ECM?
JLP
This is the 1990 Cavalier 2.2 5 speed BTW.
JLP
Either you have an Idle air control valve, or it is solely controlled by them ECM. I know that 3.1's have IAC but i'm not sure about the 2.2, it should be by the thottle body if you have one, they tend to cause problems like that. If the 2.2 is anything like my 2.0, a leak in your fuel pressure regulator hose can do that too. Just a few thoughts.
engine temp , oxygen sensor temp, and vehicle speed control the idle speed.
yes the 2.2 has an IAC and the ECM is what controls it.
You're using the mpfi ecm, right?
When you shut the car off, the ecm will completely close the IAC valve. Then it starts to open it, and counts "pulses" as it does. Somewhere around 120 pulses the ecm usually stops the IAC and that's where the valve sits until you restart the car.
When you restart the car the IAC is supposed to be open, left over from what I describe above. After the engine reaches a certain rpm, the ecm uses the values Pezed mentioned to decide how fast to close the IAC and reduce engine speed, and what to reduce engine speed to. This takes a little time usually. You generally can tell that it's happening.
If the car goes to 800 rpm right away, you have to wonder if the IAC was opened enough on the last shutdown, or if you're restarting the car so quickly that the ecm doesn't get a chance to finish "parking" the IAC. Sometimes you can try disconnecting the IAC before a restart to see if the idle speed goes high (meaning the IAC parked correctly) or if the speed stays low indicating a potential IAC problem.
Now idle speed can be seriously affected by timing, and I haven't even begun to discuss that. For now, maybe start with something as simple as cleaning the IAC passages of oil and carbon buildup?
-->Slow
Good thoughts guys.
Slow, all the passages are spotless as I had the intake all cleaned up before swapping it on. Seeing as this happened with 2 different IAC sensors on 2 different fuel injection setups, it leads me to believe it could be a wiring problem leading to a sensor.. although I have no check engine light and it does function correctly.
I'm still running the original TBI ecm. I just figured a newer ecm might pin out different, and also went off the fact both the TBI and MPFI are batch fire. Not really sure though. I have an ECM from a 93 I could try though...
JLP
The wiring for the IAC motor is tricky. You can swap the wrong 2 wires and have it work in reverse. And the wiring isn't the same for every IAC or for every ECM. If you have a spare IAC you can try connecting it to the car and doing things like opening the throttle and stopping/ restarting the engine to see if the valve opens and closes as it should.
The TBI ecm's were notorious (imo) for not doing a great job of controlling idle speed.
hth
-->Slow
