Ok guys. I think I have this one figured out, but I want to run it through here just to make sure.

We have an 86 that we are putting back together. I finally got it to fire up today. When it starts up, the engine revs uncontrollably. It will go straight to redline and keep going, like the pedal is being held down I have checked the pedal and cable, and they are not binding. I even disconnected the cable to be sure. I believe there is a large vacuum leak somewhere, but is there anything else that can cause it to do this?

 

Hello,

had the exact same problem with mine (86 gxl na) on stock engine.
Scared the **** out of me, did not stop to rev (redlining) had to push the clutch and shut the engine down.
Rolled to a safe place and had a look under the hood. (This actually happened twice before i caught the corpus delicti)

Found out it was the alternator connector-wire (you know that 2 wire cable connector)
Under hard acceleration it made its way between the spring on the throttle body right over the TPS leaving the butterflys wide open.
So the butterflys were unable to close. Leading to a high revving engine.

I dont think it may be the same cable on your car but something related to the TB, something on the TB stuck open.
Or prevents it from closing properly.
Found out today on mine while adjusting TPS that you can open/close the upper and lower butterfly/s separately.

I would check them and make sure they close correctly, i dont think a vacuum leak can lead the engine to rev to redline immediatly. But thats just my opinion.

Regards
Steven

 

I'm inclined to believe you. The previous owners of the car hacked up the throttle body, removing the outer plates and some other things. on top of that, the TB sat out in the open for some time. It's pretty rusted and corroded. I think maybe the whole thing is locked up. Thanks.

 

That could be the cause. Remember the engine needs lots of air to rev high, that air
has to come from somewhere, most likely the TB. I cant imagine a vacuum leak that
big to feed the engine with enough air to reach redline and stay there.

It might be locked, no clue though on how to fix it because I never disassembled one of those.

Regards
Steven

 

if it is running on the stock ECU it can't have that large of an external vacuum leak or the car simply wouldn't run. either the throttle body is stuck open or there is something plumbed in that is feeding air directly around the throttle plates to the intake manifold.

check to see if the knucklehead removed all of the secondary throttle plates...