OK, I don't know if this is a problem or if the car is doing what it's supposed to do. I put all my emmisions stuff that hooks up to the carb and the charcoal canister back on, warmed up the motor and set the dwell for the carb at 30degrees. Car is running great. I was driving home and was coasting down a tall bridge. I put the car in Neutral and noticed the RPM goes up to about 1300-1400. Put back in Drive and it doesn't jerk, the rpms just go down. I have found it will stay at this high idle until the car slows to under 40MPH. What causes this? I'm assuming it's a program in the computer to keep the car from dying or popping through the exhaust. I wonder how it raises the idle - by energizing the high idle solenoid on the side of the carb that comes on when the a/c is on or could it change the timing?
Anybody know what's going on here. Does anybody else's car do this?

 

It's supposed to do that. It's an emissions thing, especially in the stick shift cars.

The ECM commands the little "kicker" solenoid to operate when the throttles would slam shut too fast and let in too little air with the engine at a high RPM and thereby make the car run too rich.

If it seems like it's doing it too much, screw the solenoid plunger in a little bit (¼ turn or something) until it's better. Takes a ½" wrench IIRC. Its operation shouldn't be particularly noticeable, it mostly should make it seem like the RPMs hang just a little bit when you take your foot off the gas, like you would between gears in a 5-speed or something. A little adjustment goes a long way.

 

OK thanks Sofaking, I will try setting it lower and see what happens, it does kind of idle a tad to high when the A/C cycles off now too since I adjusted the mixture.

 

I think you need to reset the idle speeds after adjusting the mixture dwell. I had to do that on my '84 T/A after rebuilding the carb. Check the emission decal under the hood to be sure but the typical setting for a 305 carb engine/auto trans is 500 RPM in drive and 650 RPM with the idle solenoid energized. Make sure the A/C isn't running when making the adjustments.