ok i have a 94 sls 55k miles ,, i have a eratic idle (only sometimes) when it is idleing eratically the service engine soon light sometimes flashes on then goes off

i have po 23 and po 25 codes history,,,,, i cleaned up the egr valve and new pvc ,,, i have all the receipts from new on the car and looking thru them in 1994 when the car had 21k miles on it and was under warranty the previous owner had the same codes and same service light on and the dealer replaced the PCM ,,, so should i replace it ? looks like it is $130 and not to tough to do
think this will fix it ? thanks for your help!!

I seriously doubt that was the problem then or now, but yes, you can replace it if you want to. Do I think it will resolve the problem? I doubt it very much. The PCM rarely if ever goes flakey, it either works or not. When the PCM goes bad, normally you will not be able to start the car at all. There are system diagnostics to check the PCM and according to those diagnostics it will recommend a change of PCM under certain conditions. Sometimes if you remove the data cable and re-insert the cable making sure it is seated properly may be all that is needed. Be sure to disconnect the negative battery cable first. Allow yourself the time of a cold beer or cup of coffee before you mess with the data cable after disconnecting the negative battery cable. Be sure to reconnect the negative battery cable after you have fussed with the data cable. Reset any and all codes before you start the car for the first time. Let the car idle to temperature and drive it at least 10 miles before you make any decision as to improvement or not. Check for any new codes. Post them here.

I understood the dealer replaced the PCM already once, and the problem still there. So, what the point to change PCM second time?

91TexasSeville: I should say that PCM can go flakey in my experience. Even more: electronic parts have tendency to have intermittent problems even more than anything else. The PCM has complicated scheme and failure of one transistor out of thousands can lead to unpredictible results.

I wouldn't think it would be the pcm. The ses light and erratic idle could be a number of things. I had the same issue about a year ago on my 94, and it ended up being a coil pack going out on me. You can go into pcm data, I believe it is ps04 and disable one cylinder at a time to find the one that isn't firing.

If you want to go this route, post back that you are interested. I am at work now, but when I get home I will post exactly what you need to do to check your cylinders through the pcm.

How much does the PCM cost? The dealer wanted $250 plus $250 to install, I'm thinking I can get it cheaper and installation looks fairly easy.