Hey all.

I have a 2001 Galant ES with a 2.4L 4G64 that is having idle issues.

It started out happening occasionally and over a couple month's time, got to the point where it was nearly constant. The car runs fine with any amount of throttle input but it just will not idle.

Initially I checked the codes and got a error on the CPS so I replaced that. The car idled fine for a couple hours but the issue returned. So far, I have replaced or verified all of the following:
IAC, CPS, plugs, wires, COPs and battery. I also pulled the TB off and cleaned it thoroughly. Monitoring in Torque OBDII, I can see that the throttle properly shows 0% to 100% corresponding with throttle input. There is an O2 sensor error but that's been there the entire time I've owned the car.

Here are the current symptoms:
Cold start, the car idles as it should ~1000 RPM. As the temp gauge needle rises past the cold mark, there is an audible click under the hood and then the car stalls shortly after. If I try to restart, it cranks up, hits around 1400 RPM then stalls again. The only way to keep it running is to apply some throttle.

Once you get the car moving, it drives fine and has good power but the second you come to a stop, the engine dies again. I tried pulling the vacuum line off the EGR diaphram to ensure it stays closed, no change. I've reset the PCM several times, both through the code reader and by disconnecting the battery and that doesn't change anything. I tried disconnecting the MAF to force the car into closed loop mode but still no idle. I've also tried running the A/C, and trying to see if maximum or minimum alternator loads (I.E. turning everything electronic on or off) made any difference. Nada.

At this point I don't know what else to check. Any suggestions before I junk this car?

 

I would clean out the throttle position sender motor it's probably blocked with carbon.

 

Idol motor.. Can't remember the name right off the bat

 

So, after a lot more troubleshooting I finally seem to have got it semi-figured out.

I finally said "to hell with it" and backed out the BISS idle screw until the car would idle without stalling. After a week of driving, the car has not stalled once. There is occasionally some idle surging as high as 2000 RPM but its infrequent and I'm chalking that up to the PCM learning the idle after having been reset.

For the record, I would never advocate adjusting the BISS unless it's a last resort because you can cause more problems and potentially create an unsafe condition where the engine is putting power to the wheels when you are trying to slow down.

The TPS was fine, voltage output read nice and linear as it should going from closed to WOT with back probing the leads with my Fluke. Data logging indicated the same with no pedal input showing 0% throttle and WOT showing 100% throttle and a smooth climb between when gradually pushing the pedal down.

That's the IAC. (Idle Air Control) I also tried two separate IAC motors and neither changed anything.