My 86 NA idles smoothly and above 3000 it runs smoothly but between 1200 and 3000 the speed fluctuates constantly. If I raise the engine speed up to say 2000 rpm, It wont stay at that speed. It will drop off by several hundred and then raise back up to 2000 again and again. If I raise the engine speed above 3000 rpm, the speed can be maintained easily.

Anybody heard of this before. I did a search but I only came up with poor idle conditions.


ash

 

Any suggestions???????

 

check your car for vac leaks. Check you afm, tps- make sure they are withing spec. when you say speed, do you mean engine speed or actual vehicle speed? -alex

 

I mean engine speed. It happens even when just sitting in the driveway. After the engine reaches 3000 rpm and higher, the fluctuation disappears. But a lot of normal everyday driving is done with the engine between 1200 and 3000 rpm. If I give it just enough gas to raise the engine speed up to say 2000 rpm and hold it there, the rpms will drop by 3-4 hundred and immediately go back up to 2000 rpm.

I rebuilt it last winter and threre is probably about 50 miles or less on the rebuild.

 

It sounds like your TPS is out of adjustment. My car used to do the same thing until I adjusted it.

Look here if your car is a S5 (1989-1991):
http://www.johnr.com/tps.html

 

Sorry, I just noted your car is a S4. If you search, you can probably find out how to adjust its Throttle Position Sensor (TPS), because the S4's only have a narrow range one.

 

Does the 86 NA S4 have an TPS?

I just noticed that the engine runs OK when it is cold. After several minutes the problem arises.