I have a 79 with a weird problem. I inherited the car from my dad and the AC compressor has been dead for a long while. When he had the car, the defrost mode worked just fine (air would blow out of top of the dash). The problem now is that the when you move the selector to defrost and begin accelerating, the engine races at WOT. You can put the car in neutral and rev the engine but the RPMs won't drop. Today I had my wife in the car and I watched the carb when she switched over to defrost. The engine ran fine. I revved the engine a little and right near the throttle linkage, an object which looks like a bolt head popped out and pushed the throttle linkage back and the engine raced. I shut the engine off and after a few seconds the "bolt head" retracts. This part is on a bracket on the D/S of the carb and is attached by a bracket with two phillips head screws. Any idea what is causing this? Turning the defrost off while the engine is running will not cause the idle to drop back down. The only way to get the idle down is to shut off the car and restart.

Any thoughts or idead would be appreciated. A GM tech on another site said that he thought it sounds like the Idle Speed Control is not working and either it or the ECM is going bad. The thing is when I searched online for the ISC, every place I looked told me that there is not a ISC for my engine and year.

Perplexed and pissed off,

Matt

I have a 79 with a weird problem. I inherited the car from my dad and the AC compressor has been dead for a long while. When he had the car, the defrost mode worked just fine (air would blow out of top of the dash). The problem now is that the when you move the selector to defrost and begin accelerating, the engine races at WOT. You can put the car in neutral and rev the engine but the RPMs won't drop. Today I had my wife in the car and I watched the carb when she switched over to defrost. The engine ran fine. I revved the engine a little and right near the throttle linkage, an object which looks like a bolt head popped out and pushed the throttle linkage back and the engine raced. I shut the engine off and after a few seconds the "bolt head" retracts. This part is on a bracket on the D/S of the carb and is attached by a bracket with two phillips head screws. Any idea what is causing this? Turning the defrost off while the engine is running will not cause the idle to drop back down. The only way to get the idle down is to shut off the car and restart.

Any thoughts or idead would be appreciated. A GM tech on another site said that he thought it sounds like the Idle Speed Control is not working and either it or the ECM is going bad. The thing is when I searched online for the ISC, every place I looked told me that there is not a ISC for my engine and year.

Perplexed and pissed off,

Matt That is a high idel silanoid for your A/C. It works with the defrost also (Defrost used the A/C compresser). Either adjust it or unplug it. Personally, I'd get the A/C going, but then again, I don't like being hot.

I disconected the soleniod and the idle sticking problem went away. Should i go ahead and replace the solenoid or will it always stick since the AC compressor is toast?

THanks a lot!
Matt

Just leave it dissconected till the time you decide to replace the A/C compresser. All it does is incresse idel speed when the A/C compresser is on (A/C or defrost) .