Car accelerates/maintains speed on its own - NJFBOA - Home of New Jersey's Camaros and Firebirds

V · 07-03-2017, 08:13 PM

Car is a 1988 Trans am AGT, 350 TPI automatic transmission.

All stock afaik. No bolt-ons, not sure if stock block though. I was told it was rebuilt previously.

Well, the car accelerates/maintains speed on its own when cruising. If I'm doing around 20 and let off the gas and brake, the car will slowly increase speed up to maybe 30 or so before I need to apply the brakes. It's not a sudden thing, just slow and gradual. Throttle cable and blade are not sticking.

So today, I did check and readjust the TPS since I was reading that a bad one could cause the issue I'm having. Initially, it was reading 4.22V at WOT and 0.680 at idle. It seems that the 0.680 is just above the recommended range for the setting at idle. I reset the TPS to 0.540 at idle and I get 4.10V at WOT.
However, I have yet to see if this makes any difference. This morning I ripped out all the steering linkage getting ready to fix all that so obviously I can't drive the car yet.

I wanted to see if anyone had any additional input on this or if they think that slight adjustment would remedy the issue.

deadtrend1 · 07-03-2017, 09:24 PM

And it idles fine when not in gear. Only when comming off throttle it does this?

V · 07-03-2017, 09:59 PM

Quote:

Originally Posted by deadtrend1

And it idles fine when not in gear. Only when comming off throttle it does this?

Correct, maintains a low normal idle when in park. Doesn't even really rev up much from a dead stop, only acts up when already moving.

deadtrend1 · 07-04-2017, 02:43 AM

Its the ecm aftermarket or does it have a aftermarket chip (JET for example)?

V · 07-08-2017, 07:19 PM

I assume it would have the stock prom.

I got the steering and front brakes all back together today and got a chance to take it for a test drive to see if adjusting the TPS to within the specified range. I feel the acceleration issue is now completely gone and the maintaining speed issue is 99% gone. It might be completely gone too but there were a few times I felt it should have slowed quicker but perhaps it was just the slope of the road or at a certain mph. Overall, when I left of the gas, the mph dropped almost instantly and decreased slowly as you'd expect an automatic transmission car should do. So I think the TPS adjustment did the trick. I also don't have any more surging when trying to apply the brakes.