i have an 86 efi motor in my truck. a high idle has led my motor to do the wonderful up and down annoyance while pressing the brake pedal. instead of just clipping that fuel cut wire i wanted to fix the real issue. the original throttle body was gummed up and sticking and didnt close all the way and all that. i originally thought this was my issue. ive replaced the throttle body with a good junkyard one and im still having my idle too high. ive played with the screw and it doesnt seem to be doing anything. i can turn it all the way in and am still having too high of an idle. i replaced the oring on the throttle screw too just in case it was leaking because it looked really bad. the motor is equipped with ac but i have never used it. this problem has been pretty constant even in the 86 donor truck. any ideas?

 

^ I was having the same issue, and I just slowly went over everything. I checked the timing, made sure to put the jumper on and dial at 5. Then I set the TPS, which was way off. Adjusted the dashpot, and now its freaking smooth.

I had also previously replaced the TPS with a new factory one, but was unable to adjust it appropriately, until I found a cool thread on here where Abecederian explains how to adjust the TPS with the truck on with the jumper. That alone made a big difference. But I would still get a high idle occasionally, and that was not resolved until I adjusted the Dashpot.

I would make sure that those three things are correct first. If all of those are fine, I would start looking for a vacume leak.

 

I had the same problem as well, I replaced the return spring on the throttle where it connects on the side of the throttle body, I would recomend buying a new spring though because I replaced myne with a spring off of some honda 4wheeler brakes and my gas pedal is stiff as can be now!

 

does the idle still go up and down? air in your coolant system can cause this

 

mine was like that too. it was how my donor truck came, with a big aftermarket spring on there. turned out my throttle body was worn out and the valve wasnt closing all the way thus a bigger spring to hold the valve closed at idle to help maintain the idle speed. try wiggling the rod that connects to your butterfly valve and see if its lose. mine ran wayy better when i put a good junkyard throttle body on it.

 

I have the same issue but i think its becuz it's cold out cuz its the only time it will do it i will start it up and it will rev up to about 2 grand and rev down to 1 grand for about fiv miniutes then its ok