High Idle, then failure to maintain idle
 

I have a new to me problem that I did not see when looking around the history. I have an idle on an '83SC that will start out fine and then rise when warm to 1500 to 1800 RPM where it sits. Turn the motor off, wait ten or so minutes, turn her back on and the idle will not stay over 300 RPM until the car is driven for some distance. This occurs when the temperature outside is 70 or 30. I have the idle adjusted completely down. I did not find any binds in the linkage, but feel I should go back and lube the linkage one more time just to be safe. I do have oil leaks and plan on going back in at some point and re-building, again, to take care of the seals. No burning of oil, no strange sounds, good acceleration, smooth feel. I do have an A/C that is disconnected and waiting till I feel like replacing the blower unit (I am rather cheap...). Could this be the infamous cold start unit, or could I have a bad A/C switch that is telling the car to increase idle to compensate for the A/C being turned on? Any thoughts (short of selling the little girl, of course) are appreciated.

Your aux air regulator may be disconnected or not getting 12v.

Joe

Joe,

Thanks for the response! I lubed the accelerator linkage, disconnected the aux air regulator and cleaned the terminals. There was some oil in the area. I put the terminal back together and started the car. I adjusted the idle back up while the car was warming up. Upon reaching operating temperature the idle started climbing again. I adjusted the idle all the way down and eded up at 1400 RPM. Could this be a symptom of the regulator having gone bad?

Does anyone else have an idea? Thanks,

Just to add some possible thoughts: the high idle sounds like too much mechanical stop screw adjustment, an IAC motor thats shorted, a vacuum leak downstream of the throttle body(check with propane), or mabye the timing is advancing for some reason.

It almost sounds like its getting too much gas when warm and/or not enough when cold. Cold start system?

The fact that it changes completely when you restart it might mean that
1. the 1400 rpm stopper setting is set for a correct idle speed and something is adding to it or
2. the 300 rpm setting is right and something is really really changing it at startup.

Check for any leaks on the vaccum pipes.
 

I had a simmular problem with my 930, after I check and change all tubes and pipes the problem was still there.

My problem was on the vaccum pipe to the brakes, it was a crack in the pipe just above the gear-box.

/Jocke

Thank you for all the suggestions. I took the breather cover off the Mixture Control Unit so I could see more easily around the units and noted that the plug connector was not connected. It must have worked off somehow. I plugged it back in and started her up. Idle settled at 1100 RPM and stayed straight for two minutes. Then slowly climed to 1500 RPM. I tried to bring the idle down by tapping the accelorator pedal to no avail. I then disconnected the O2 sensor. 950 RPM and steady. But I did note the sound quality of the exhaust changed. Has anyone else noted this? I also found another connector disconnected that I do not remember where it goes. I will have a photo posted tomorrow if I cannot find it in my photos or books today. Thanks to all,