Greetings,

I've been having RPM issues and have tried most everything and before I dropped any more $ I wanted to get some additional opinions.


Car:
Stock 92 Z28
350 TPI
Automatic Trans
157k mi
2nd owner (since 94 and 25k)
Clean, well maintained and garage kept for last 10 yrs


Issue:

1. At factory idle and timing setting car will:
   1. Stall out while in gear at a stop
      1. Trans in Drive, foot on brake
   2. Stall out when shifting from Drive to Reverse
   3. Stall out with AC on
2. Had to manually adjust the throttle position screw up to keep from stalling (after trying 7 things below) now:
   1. RPMs will not remain stable with a stable throttle position while driving
      1. Driving down the road at 60 mph RPMs will fluctuate 300+- RPMs
   2. RPMs will jump up to 2500 at start and stay there for 30 seconds before idling down
   3. When using the AC the idle had to be set to 1500 RPM with AC off, so when the AC is on the idle doesn't drop below 1000 RPM and stall out

Things already tried:

1. Tested O2 sensor
2. Replaced Coolant sensor
3. Tested TPS Sensor
   1. Checked volts against computer reading
   2. .54v on both
4. Replaced IAC Valve
5. Plugs and Wires are good
6. Replaced Cap and Rotor
7. Replaced the ignition control module

Questions:

1. Does all of this point to the ECM?
2. If yes I wouldn't mind upgrading the ECM and/or PROM to gain additional performance
   1. Open to suggestions

Any help is greatly appreciated, because I know turning up the trottle position screw is not the ultimate solutio and it's getting to the point where I almost don't enjoy driving it.

Peace,
C

 

Check your injectors with an ohm meter. I had a similar problem and after checking, I had two injectors that were bad. I replaced them all and my problem was fixed. Also, vacuum leaks can cause irratic idle/surging as well. The ecm attempts to "fix" a out of spec situation and the result is the car surging between extremes.

Ken