2001 Pont Grand Am - 3.4L Won't Idle

[Ruger77]

We have a 2001 Pontiac Grand Am 3.4L that intermittently won't idle.

We have not been able to duplicate it yet here at the shop, but it does have a Code PO122 and PO1122 for low TP voltage and or short. The back story on this car is: we installed a new PCM, TP sensor, oil pressure sendor 3 mo. ago (3500 miles) for a TCC problem. Customer said car has been great ever since, until the other day it wouldn't idle. He drove it that way all day, then it started idling again. I have wiggled the TPS wires while watching the voltage and the voltage never moves.

Should I warranty the TPS and clear the code and let him try it?

[liljoe]

Given the codes it had and the fact that these are common failure parts, I would replace them and explain the situation to the customer and try to make sure they understand that ou could not re-create the problem.

[steven kiser]

i would warranty the tps without hesitation. as stated above i would explain to the customer what and why. i strongly advise against mentioning a high failure rate. i would check the air filter to make sure it hasn't sagged or been compromised. did the car have to be jumped or started particularly hard that morning? i've seen problems like this from dead battery issues. another quickie here, make sure the secondary grounds are clean and secure. a loose ground may force a search for another and cause electrical issues like this. i've seen some real weird issues before because of loose grounds. along these lines make sure the bolt is clean. i've run into issues where an intake bolt was used as a ground cleat and even though it looked great on the surface it was a mess inside. a spike in the alternator will cause a pcm issue. i would check the alternator with a multi meter that has a bar graph to make a glitch more easily read.

[Ruger77]

Ok, thanks for the help. I finally got it to act up. TPS volts were good during the "no idle event", but when I went to the functional test for the IAC control, it would not change the IAC counts, or idle up the engine. The IAC counts were 255 at that point, and would not go up or down when commanded. After it started idling again, I could change the rpm with the scanner. Tapping on the IAC did not help, nor has wiggling wires or connectors helped. I did warranty the TPS and I installed a new IAC motor. Now trying to reduplicate.

[liljoe]

Sounds like a poss ECM issue to me.

[Ruger77]

I hope it isn't the PCM....we put one on in Feb. I have not been able to duplicate after putting on the new IAC. Probably will let the customer have it and see what happens. Thanks for the help.

[ricmorin]

Was it OE or Aftermarket?

[Ruger77]

Aftermarket.

[ricmorin]

Is it one of those that comes programmed? Or did you do it? I've had trouble with some non-OE units. I only install OE now. Far fewer headaches.

[Ruger77]

It was a Delphi and Napa flashed it for us.

[steven kiser]

i'm going to jump in here. delphi may be a good product and g.m original but, and it's a big but, some remanufacturers or manufacturers will make changes in their product to accommodate their customers needs. you may not be getting the same product you would from world pac or the dealer. the only tool that i use for the reburn is the tech 2 and i only use oem or i will use the delphi brand through world pac. when you tried to change rpm through the scanner did you have the iac back probed? as a rule if i can get it to malfunction i'll back probe while controlling. this eliminates any questions.