1987 Corvette Surging Idle, No Response to Throttle, and Idling High in Park.
 

Hey everyone! Just opened up an account here after years of just reading through the threads. So let me just cut to the chase. I have a 87 auto that I drive on the weekends. Today I was driving and wanted to give it some juice and all of a sudden the RPMS dropped to idle and the car started bucking. Then when i let go of the throttle it started revving on its own. All when I'm on the road! Luckily I was close to home and just put the car into park. When I did so the cars idle jumped up to 1600 RPM. Then it started revving on its own from 1200 to 1600 RPM. Again when I tried to rev it a little it would sound like it was stalling then return to high idle when I let off. I've been reading through the forums saying vacuum lines could be the culprit. I checked a couple months ago all the lines and it seemed as there were none. I also in the past years have replaced the injectors (6 months ago), fuel pump (10 months ago), brake booster(6 Months ago), sparkplug wires and sparkplugs (over a year and a half ago). Im sure there is more. So my question is, what could it possible be? Thanks in advance :)

First off I would determine manifold vacuum; if no issue move on to fuel pressure.

After doing some looking around, I believe I may have a bad fuel regulator. I've changed injectors and fuel pump but left the regulator. Do you think this could also be the cause?

I haven't looked anything up but do you think it could be a defective TPS? I would check the resistance while moving the throttle just to eliminate that. No codes, correct? I would check for codes anyway. Sometimes set what I call soft code. Set a code but no light. HTH.

Joe K.

I had something at one time: cold start especially when the weather was colder and the car would start normal but a little high on idle. Drive about 4-6 blocks typically and when the engine temp got around 160 degrees the engine would buck so bad it barely ran. Get it home and in the garage and let it set about 30 minutes and it would start and run fine though the idle was a little high. In every case there was no code to be found. Finally tracked it down to apparently the IAC was sticking apparently. The FSM kept leading me to the computer lost connection but that didn't appear to be the case. Happened I had a plastic faced hammer one day and rapped the IAC with it a couple of times that seemed to have fixed it.

Mines a 86 L98 with a manual transmission.

Good luck on your issue and hope it helps someone.

In my case, I was at a low speed and I floored it. Then nothing happened and it started bucking if I tried to reapply throttle. Then I got home and the car was idling at 1600 rpm. If I tried to give it some throttle it would burble and try to stall. Im gonna take the tpi and take a look at the fuel pressure regulator diaphragm anyway.

Any codes?

Just checked all the codes with a GM Code reader. I got 22 (TPS), 33, 34, 36 (All MAF and MAP Related). So I guess this is where I start. Thanks for everyones input. Parts are gonna be collectively $150 so not to bad.

Do some research on the code 36 before installing anything! Many current MAF "replacements" do not actually work with the burn circuit from the ECM.

Get an FSM if you don't have one, run through the electrical tests. I had a code 36 for a long time, finally went with one of the replacements that eliminated the burn off and had my ECM MEMCAL modified to disable code 36 checking.

Good luck, code 36 has been a real pain to many of us.

Clean your connections with electrical cleaner and set your tps to .54 volts at idle. Then check for smooth operation(not jumpy) to 4.0/4.5
:cheers:

Seems strange to get all those codes at one time, look at a wiring schematic to see if thay all share a common power or ground connection. Just trying to eliminate parts replacement before the actual problem is addressed.

Here's an old thread that might help on the code 36: https://www.corvetteforum.com/forums...-36-fixed.html