This is on a 350 TPI motor. The car starts up and runs fine for a few minutes but shortly it starts running rough. If you are out driving it it runs fine. When you come to a stop the motor will start surging, it will almost stall and then surge. I guess this is the IAC kicking in. So I borrowed a buddies engine scope to take some readings, here they are below. I was told I might need a heated 02 sensor because I have headers, let me know what you guys think...
All tests were done at idle

Spark Advance : 15 degrees
TPS Volts : 0.58v
Knock : 0
Idle Speed : 700rpm
IAC : 13
INJ PW : 1.5ms
MAF : 006-007 G/S
02 Volts in Open Mode : .25-.36

The car runs lean at idle and I watched the computer would switch back and forth from OPEN LOOP to CLOSED LOOP, never held a constant. I am going to go run it again and see what happens. If there is any other information you need, let me know and I will try to capture it.

 

Is your O2 reading varying? During cruise for example, on a scanner it should switch back and forth between RICH and LEAN, as it's attempting to hold stoich but a standard narrowband sensor can't do this precisely.... If the O2 is fubar, could explain some of your issues. Still, dont see why headers would require a heated sensor. Only point for that is to get the computer to achieve closed loop faster, until the O2 becomes hot enough that it gives a varying signal so the computer knows it's working, in which case the computer can go to closed loop operation.


I'm betting your O2 is bad. Here's why. It's reading lean at idle. But you're surging, which is a rich symptom. When O2's fail, they typically fail "safe", in other words, they fail reading lean, causing the computer to keep dumping and dumping fuel, until it maxes out its trim, causing you to be way on the fat side, while the O2 STILL reads lean.

Any of the ECM gurus on here could probably tell you the trim range of the injector pulsewidth, since thats how the computer adjusts fuel, it may give you a clue as to what the computer is trying to do to your air fuel ratio.

 

So how can I tell if the 02 is working properly, the voltage does vary. It will get much higher in voltage when the computer moves into closed loop mode. Up around the mid .40's-.50 range, then it jumps back to open mode and goes back down. Again the engine is jumping back and forth between open and closed mode and this was after 10 minutes of running. I am going to go out and run it some more,.

 

Well it seems I got it into closed loop mode, probably because of how hot it is today. But anyway, it went into closed loop and it was switching between rich and lean while in closed loop. The car smells bad though, strong odor from the exhaust. I am confused.

 

Like I said, rich and lean is normal, that's the computer attempting to hold stoich...

It's still possible the O2 is bad. O2's for a third gen are $20 last time I checked, if you haven't replaced it or don't know how old it is, it's worth the $20 to get it out of the way.

 

Try disconnecting one injector and see if the idle becomes stable.

 

The only problem with the lean/rich switching, is the O2 sensor is on the drivers side manifold. If the passenger side is running rich, the O2 wouldn't see it.