Hi All. Thanks in advance for your thoughts and comments.

Just picked up an 89 IROC Z. 305 F Engine. I know that the following have just been replaced:

1) Idle Control Motor
2) Throttle Position Sensor
3) ECM

We thought this had fixed the previous problem, and to an extent it is better, but not completely.

It starts and idles fairly well. However, at times it surges and then the idle drops down and runs very rough, but it seems to catch itself and usually idles fine after that. This isn't consistent.

When you put a code reader on it, (and the code reader always shows a code 12). But, at times, it seems that there is a quick pulse, the check engine light pops on and flickers and if the electric fans are running - they will shutdown briefly. Then the fans start running again and the check engine light goes out. This is when the car is in Park.

We have looked for any obvious short in wires, but the only thing that I can see is that the backup lights sometimes stay on when the car is put in neutral or drive. I know there is an after market lockout shifter on the car, but per the previous owner, he never had a problem with it.

That's it. Any thoughts would be appreciated.

 

aha! your P/N switch plays a part in all this. personally id throw away that shifter, and get a stock one. THEN make sure your P/N switch is good /adjusted correctly.

 

Thanks Rusty,

But unfortunately that is the least of my problems right now.

Local shop replaced the ECM and I took it for a long freeway run. It was trying to die before I ever got to the freeway. Once there it seemed to run okay for about 20 miles, then it sounded like it was loading up, cutting out, erratic idle, and kept trying to die. Stopped for a burger and after restarting, died at stop sign. Back on the freeway and same type of behavior all the way back.

Pulled into local big auto store supply and had them stick a code reader on it. There were so many codes I thought I was in the matrix. 24, 26, 34, 36, 45, 46, 51(Twice), 52, 61, and 63.

Not wanting to leave it at that, I bought the Innova 3020D. I removed the negative battery cable last night, and then waited until this morning to start it up again.

It starts right up and immediately went to 2500rpms. After 5 minutes I tried stepping on the accelerator a couple of times to see if I could get it to kick down. Nothing doing. After another 5 minutes running at 2500rpms, it finally kicked down to around 1200rpms and then in another 2 minutes it started to sputter and the idle started to fluctuate (sounded like it was loading up again).

When I put the code reader on it, I got the following codes: 36, 43, 45, 46, 51, 52, 54, 54, 61, and 63. I guess I should ask myself how it starts and run at all!

At this point, after having spent over $600 for a diagnosis and the replacement of the ECM - I'm not sure where to go from here. As I mentioned the Idle Control Motor and the Throttle Position Sensor were replaced about a week before that.

According to the shop that repaired it, there were no vacuum leaks and the injectors were clean and running fine.

I may not have any hair left after this ordeal.

 

heres what I would do ,at this point. buy yourself a factory service manual. start with the first codes and work your way to the last. the manual explains what each code means in depth. AND gives you the knowledge to repair it intelligently. I also would stay away from "shops" they don't know anything about a car this old, and they don't care about it like you do. it can be done, and its not as hard as it seems.good luck and let us know how it went.