Brianbajnuth

Hey guys I have a 87 gta trans am. I'm having a issue with SOMETIMES I have a code 42 at cold start and runs rough and stalls sometimes. But when the engine warms up the code goes away and runs fine after that. What can cause this?

Brianbajnuth

Anyone? Trying to fix this before it gets any colder out

Brianbajnuth

Bump

TPIFBody

Hey Brianbajnuth--


I'm a recent registered member, but I've been reading these forums for several weeks. Lots of great info, but a bit sparse on my particular problem.


Curious if you ever resolved this problem with your 87 GTA?


I'm having a similar issue with my 86 IROC 5.0 TPI.


The car sat for several years before I ended up trying to resurrect.


I've rebuilt the entire fuel system including tank cleaning, new pump, new sending unit, new lines, and new filter. It's got good fuel pressure (42) that holds for hours. Fuel pump relay checks good.


Complete tune up - cap, rotor, plugs, module. Even replaced the RFI cap & harness. (Big HEI distributor with coil in cap - all GM stock parts).


At cold startup it comes to life immediately but it doesn't do the expected rev-up and settle down to idle RPM. Just goes immediately to around 600 RPM and then sets Code 42. It will then run OK but not very strong, stumbles, and poor response (because ECM is not adding any timing).


Here's the weird part... After I let it warm up a bit while showing Code 42, I then shut it off and clear the code by removing ECM power. When I restart, it revs up and settles to 750 RPM like expected and does not set Code 42.


I have followed all of the troubleshooting guides including the one in the factory service manual I acquired for the car. All ECM/HEI wiring checks out. I've replaced the ECM. I've replaced the chip (and even tried a Hypertech version). I replaced the IAC, thoroughly cleaned the throttle body, and went through the entire IAC reset, throttle plate idle speed adjustment, and TPS adjustment procedure. The TPS works fine. I replaced the CTS and it works fine. I've collected 160 baud data and nothing seems out of the ordinary. It goes closed loop and runs terrific after startup without the Code 42. One peculiarity is that without the Code 42, with my dial-back timing light I see timing advance upwards of 50 degrees at idle. My base timing is set to 6 degrees. When running without Code 42, if I disconnect the EST wire the timing immediately drops and a Code 42 is set.


I'm at a complete loss for what else could be causing this problem. It certainly seems heat related. I have not changed the ignition pickup coil and I'm about to tackle that but I don't have a lot of confidence that it could cause these symptoms. I don't want to get into a mode of throwing parts at it hoping to get lucky and cure it. A few "auto parts store experts" have suggested things like replacing the O2 sensor and checking fuses. I believe I'm well beyond that level of "outpatient" diagnosis and I'm in need of a "skilled surgeon" to comment on this strange issue.


Any advice or suggestions from the members will be greatly appreciated. I want to get this car running correctly before I proceed with the cosmetic resurrection needed to bring this car back to the cool ride it once was.


Cheers.

Brianbajnuth

When I had the problem I ha changed the pick up, icm, coil, cap and the problem went away also check to see if your coil is grounded