I have been trouble shooting a surging/hunting idle problem on my mostly stock 84SE. It seems to be searching and goes from 2k to 8k. So far I replaced the dist. cap, plug wires and plugs. Sprayed carb cleaner around the vacuum lines looking for a leak, cleaned and check the BAC, sprayed cleaner on/around the throttle plates, checked timing and tps setting with no luck. Tonight I disconnected the tps and the idle improved with only a slight hunting issue.

Tomorrow I will further test the tps and will swap with a spare unit on hand. I am wondering if there is a chance that by disconnecting the tps for a better idle it is masking another issue or the tps is really the issue.

Just to make sure I did not miss anything setting the tps here is my method. Start the car and run to full operating temps. and then turn off. Connect my two test lights and turn the switch to the on positon. Adjust tps to where only one light is reading current, between both lights going out and both reading current. I will push/pull on the throttle linkage to make sure not to border line one way or the other.

 

That's a pretty long range for it to be searching. I've had a badly adjusted TPS before and the worst I had was a really bad idle and issues while driving it with surging. The only real time I had a real bad surge like your describing was when I forgot to hook up the vacuum line to the BAC valve... and man that was bad. It hunted all over thousands of RPM's. When you adjust the TPS, can you hear the relay click in?

 

It has been over a month I spent attempting to correct my idle issue. The other day I decided to pull my dizzy out of my well running gsl and put into my SE to see if maybe it had anything to do with the ignitors. Made the swap and disconnected the GM modules I was using in the SE and the idle was rock steady. I was banking on the module in the trailing position as the issue and had both of them tested at Advance, they both passed, WTF! I went home and installed the GM modules back in and tried a different dist., idle went back to ****. The only way I found to correct it was to advance the trailing timing. Decided to take the original dizzy and put j109s back on it, got my idle back with the correct timing. I am going to swap my GM modules for new ones (lifetime warranty) as I still believe this was my original problem despite the fact them being able to pass the bench test.