90 3.1 runs like POS PLEASE HELP!!!

I have a 1990 Grand Prix with a 3.1 auto and I am stumped about why it is running like a POS. It surges at 5-15 MPH, idles rises to 1000-2000 RPM when in Park or Neutral, and in drive the RPM's stay at about 1600 and when I come to a stop (at about 3-5 mph) the RPM's drop to around 500 and it barely idles. I have replaced the IAC valve, TPS sensor, MAP sensor, one of three coils(ignition modules), fan motor, coolent temp sensor, fan relays, and the radiator. I also found out that cylinders 2&5 have only 75lbs of compression and the rest have 120lbs. I was told that it could be that the computer is making the motor idle high because it is overheating. Trust me, it's NOT. Also I'm not sure if this has anything to do with my problem, but the 'low fuel' light and the 'check gauges' light are always on. Some times the 'service engine soon' light pops on also. I bridged the A and B terminals on the DLC and found out that the trouble codes stored were 'idle speed error' and 'Electronic Spark Timing'. The car also will not stay running when the motor is cold. I hate driving with 2 feet.

I'm sick of guessing and replacing parts out of the blue, it gets quite expensive. :banghead:

Any suggestions/help would be greatly appreciated.

Thanks in advance,
Mike

The guess and buy method is never a good way to fix a car.

Have you done an idle-relearn on the car yet? If not..then go here: http://www.60degreev6.com/index.php?p=pages&pid=74

Try that and see if it solves your problem...or at least helps....since you replaced the TPS and IAC and probably didn't perform the procedure.

On the website that you named it says to start the car w/out pressing the gas. My car will not start unless I give it gas. Does this affect the relearn procedure if I press the gas only to start it and get it to idle?

You can give it a try..but I'm not sure if it will learn correctly if you give it gas to get it to idle.

Have you checked your fuel pressure?

I have not checked the fuel pressure yet but I only have to press the gas for a second or two to get it started. Then it idles by itself.

For the point of your check gauges and low fuel light being on all the time I had the same problem with my grand prix. There's a cold soder on a chip in your gauges. http://www.w-body.com will show you what to resoder on it look under Problems, Repairs and Prevention on the main page.

If after the relearning is done you keep the problem, then check you do not have on the intake manifold any air leaks or dents that could allow more or less air flowing to the plenun depending on engine temp. That is a possible herratic idel cause.