Hi I have been looking through posts recently to try and figure out a problem I am having with my 1989 corvette convertible. Hopefully I can get some guidance here. My car sat for roughly ten years and I got the car running a couple of months ago. I was getting a maf code and a timing code. I have since fixed the maf issue.
I have installed a new maf, maf relays, plugs, wires, cap, rotor, coil. I also checked the timing which was right on.
the car was originally running like crap but the car now runs awsome just like it used to. but I still am getting an intermitant code from time to time. it is a code 42. I want to change my e.s.t. sensor within the cap rotor assembly but someone also suggested it could be my ecm. how could I test to narrow down which could be causing the problem? right now the car runs great but every couple of days it seems like someone is flipping a switch while I am driving it on and off. the car doesnt die but it sets off the code then if I let off the gas it seems to clear itself like nothing ever happened.... Any suggestions would be greatly appreciated...

 

Sounds like an electrical connector pin issue. Check the EST connector for any corrosion - use magnification is possible. Does the issue seem to be temperature related; ie., does the problem happen only when the underhood temperature is high or low? If high, it could be the EST module itself. The ECM is another possibility ... but I don't know how reliable that unit is. Anybody?

 

Here is the trouble tree for code 42.
Good luck

 

If it was the ecm would it be intermitant? I would think if the ecm was bad it would just not work?

 

gbrtng it does seem that this issue occurs when the car is warmed up but as I stated some days the car runs like a raped ape and out of nowhere someone is flickin a switch and the engine is cutting in and out..... Maybe I will just change the est module... I thought there might be a way to diagnose before just replacing one or the other.

 

here it is

 

I had an intermittent ECM in my 91 - drove me nuts trying to diagnose it.
Would set 3 completely unrelated codes and after my friend spent an hour with his Tech 1 I decided to replace the EST. No good, same problem. Picked up a rebuilt ECM from a junkyard, popped the MEM-CAL in it and all has been OK for 4 years or so. Turns out the 91 ECM is a common GM part across 10 carlines or so. Don't know about the 89 however.

 

Like the 91 the 89 ECM is also common to many GM cars and trucks....the Memcal changes it from a Cavalier to a Corvette.

Look at the "Detailed Applications" portion of the following link

http://www.cardone.com/English/club/...ARTNUM=777165#

 

thank you so much for your help everyone. I guess I will start looking for a ecm and a copy of the fsm for my car. my brother in law is a mechanic and has access to some good programs for diagnosing but I am sure the fsm will help me. Once I have changed out the parts and have figured out the problem I will post my fix. this intermittent stuff is a pia to diagnose without dropping alot of $.....

 

If anyone has suggestions to where I can find one from a trustworthy person or place that would be appreciated as well. When buying a used one how can I trust it is a good one and the right one for the car. I just saw one on e-bay for 250.00 for a 4+3. but I am not sure if my car is a 4+3 . I think that refers to the transmission right?