Questions and Answers

Another Olds Idles High

Q. Greetings,

Model: Oldsmobile Cutlass Supreme
Year: 1992
Engine: 24 Valve 3.4L V6
Mileage: 115,000

Background Info:
I purchased the car new in 1992, and have put 99% of the 115,000 miles on myself, so I have a good "feel" for how the car runs. I have an electrical engineering background, but little experience with cars other than learning as I go when I attempt repairs.

Problem:
The car runs great until the outside air temperature gets below about 35 degrees F. If the car sits (engine off) at that temperature for a few hours, when it is stared the engine races to 3000+ RPM. The only thing keeping it from redlining is the computer will not let it go over 3000 in park. The idle drops to about 2000 when I put the car into drive, but it makes braking difficult. The idle should be around 800-1000. The engine slows down a little after driving for a while, but even after 20 minutes of driving at 55mph it still idles high in when in PARK It seems independent of engine temperature because engine temp reaches 200 degrees within a few minute, but the problem does not go away unless the car has been running for 30-45 minutes.

Recent Repairs:
I have replaced the following:

• EGR Valve (I was getting a code 32)
• Throttle position sensor
• PCV
• Idle speed motor (I think that is what it is called. It opens/closes an air intake in the throttle body.
• I have also looked for bad hoses, but have not found any (that doesn't mean there aren't any)

I am now thinking it is a computer problem. The computer is located inside the passenger side fender in the engine compartment. My theory is that part of the engine compartment takes the longest to get warm from the heat of the engine. I believe once the engine compartment is hot enough to warm the ECM, the car runs ok in the cold (that is my theory anyway). However, computers are not a cheap guess and I was wondering if you had any ideas before I spend the $$.

Also, I stopped driving the car in the cold. I can't imagine firing up a cold engine at 3000+ RPMs is a good thing.

Any help would be greatly appreciated. Thank you very much.
David

A. The general rule of thumb is when everything else checks out okay, it's the computer. In this case there's some other things that need to be checked before we can condem the computer.

One thing is the Engine Temp Sensor. If it is reading wrong or just bad, it will cause the symptom you describe. The Idle Speed Control (ISC) motor can be bad as well. These can be most accurately tested with a scan tool.

One other thing that could cause this symptom is a dirty throttle chamber. What I would suggest to do is take off the air inlet tube at the intake manifold. Then clean out the throttle chamber with carburetor cleaner. Open the throttle plate by hand to get to both sides of the plate. Do a good job, you have 8 years of gunk to clean out. Take off the vacuum lines going to the throttle chamber and shoot some cleaner into the ports. Then spray the throttle shaft while you move it back and forth. Once you have it nice and clean, spray the cable, linkage and throttle shaft with some CRC 5-56.

When you're done, put it back together and start it up. It will start hard due to all the carburetor cleaner Let it run for a while then take it for a ride.

If that doesn't take care of it, then have the system scanned and find out exactly, if anything, is wrong. If it checks out, then the chances of it being a probem with the computer goes up substantially.