95 3.1L Idle issues
 

Hello, first post for me. A little background on the car first. I'm helping a friend with a 1995 Monte 3.1L that has been sitting for a few years. Its a pretty nice car with fairly low miles.

When I first saw the car it would start up rev to 3000 rpm and then slow down, stumble and die. The next start would require manipulation of the throttle and it would fire up and run with a well settled idle and run normal until I shut it off.

I removed and cleaned the throttle body and mass air sensor and replaced the idle air control motor. Then when starting it fired right up and revved to 3000 rpm and would hold at that engine speed. I changed the throttle position sensor and recleaned the mass air sensor and it stayed pretty much the same. I took it for a fairly long drive and then the idle settled down and started up fine without any over rev.

I drove it to work today and it started nicely and idled properly, but 2X in the 8 mile drive the idle speed ran away and would not come down without shutting it off and restarting it. The restarts were normal.

One other little oddity is that the CHARGE light is on most of the time, but the car continues to start and doesn't show any signs of low charge.

Any ideas?

Ed

Welcome to the forum. If no check engine lights are on I'd start with the pcv valve. Then check the intake for leaks if its still having problems.

Here's things to check/change (in order to what I think based on your description):
- IAC (Idle Air Control), bolted on the outside of the Throttle Body
- Check for vacuum leaks, loose fitting lines (easy way to check is mist starting fluid around the vacuum lines while the car is idling and see if the performance of the car changes)
- Change fuel/air filters
- Change plugs and wires

Saturday I put on a brand new IAC, checked for vacuum leaks at locations in the general throttle body area and connected to the intake tract, has clean air filter. It just threw a code for bank 1 too rich and then stopped starting. Turns over very well, no start even with throttle manipulation.

Ed

Was it Bank 1 Sensor 1 it threw a code for? If so, I believe that's the upstream O2 on the exhaust manifold. It's not a guarantee, but the upstream O2 could have bit the big one (those are supposed to be changed every so often, I think 70-100K miles). The O2 sensor has a heated element and if the O2 sensor is not doing it's job right, the car will not run right.

If you replace the O2 sensor, stick to AC Delco (preferred) or Delphi. Other O2s may work, but keep in mind, the PCM is calibrated to the OEM one the best!

If you don't know when plugs/wires were last changed, I'd still do those while you are at it. This will also let you see the condition of the plugs in the cylinders and see perhaps if one cylinder has a specific issue based on the condition of the plug (helps narrow down your range of problems). Also, stick with AC Delco or NGK plugs. DO NOT put Bosch plugs in, they suck in GMs (not sure about other makes).

None of this guarantees a fix, but it's an attempt at covering the basics.