I just had a new ECM put in my car (89 GTA L98). The first couple of times it ran (I only drove it for about 3 minutes each time), it ran kind of rough (lumpy idle, and kind of rich), almost like it did prior to going into the shop. Then I took it onto the road and drove it for about 25 min. It ran kind of rough and idled high initially. Then it cleared up as I got going but the service engine soon light came on. I drove with it on for about 10 min. I shut it off for about an hour then came back to it. I turned it on and it idled EXTREMELY high (like 1800 rpms). I put it in gear and drove it and it immediately idled down and drove great. It never idled high again (I drove it for another 45 min.) and every time I started it after that, it never idled high at all (it would idle at 1100 rpms upon start up with the last ECM).

I remember reading somewhere on these forums that either when you intsall a new ECM or some other new electrical component, the car will still run kind of rough but get better as it goes as it is collecting more data. It seems that that is the case with this car. Any thoughts anyone???

 

I am going to say no, seems like there is still something wrong. The only thing the ECM will 'learn' is a fueling adjustment. It does this via feedback from the O2 sensor.

Pull the codes and see what they say.

Al.

 

Actually, now there is nothing wrong. It has been driven more today (~ 50 miles) and no check engine light and the car no longer idles high (a problem it had prior to the ecm change).

I guess what you mentioned makes sense though as prior to it fudging out it was burning rich along with the high idle. Perhaps the ecm could no longer make the adjustment or read the O2 sensor messages.

Well, until I see the check engine light again I am not going to read too much into it. But if it comes on again I will definitely check the codes.