Help! bouncing RPM and a lunging car
 

This is on my '99 Grand Prix GT . . . . . .

Problem:
When hopping on the highway, I give the car mild throttle - next thing the RPM starts to bounce anywhere from 2000-3000 in 500 increments. The car just lunges back and forth until I get up to speed or give it more throttle. Before you say plugs, wires, and/or 02 they have all been changed and have less then 6K on them.

Take the car in and have the PCM programming checked out, as well as any possible updates to the programming, and or have the 4T65-E checked out as well... There must be an issues in there somewhere..

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Before I say plugs and wires?

Pull your plugs and inspect them. They'll tell you if you have a misfire (and which cylinder it is) or if you're running lean.

Check the resistance of the wires while you're at it. And also check your coils using the procedure in Techinfo. You have an ignition problem.

Throttle position sensor

Marmot

Throttle position sensor would likely cause a problem at idle, and disable the cruise control, as well as sometimes prevent the TC from locking up on OD.

And it would throw a code and SES light, which he didn't mention.

Hey willwren,

I notice you mention that a bad TPS would disable the cruise. I wonder if you've seen my thread here: http://www.bonnevilleclub.com/forum/...ic.php?t=33927

I intend on taking the advice to change my vac lines, but I'm also wondering if something I did in the TPS change might be the cause. Any knowledge you might have is of course appreciated.

Thanks.

Bill

There are HUNDREDS of things that can take your cruise out. It usually isn't the TPS (for long anyway) as that's the one thing that will throw a code.

Thanks willwren!!

(I haven't had a chance to dig up your other topic....PM me a link)

Too damn many posts a day to read them all now.

No codes past present - no misfire
02's - fine
Checked plugs - gap fine, color fine
Checked wires - resistence was not jumping or high

While I was under the hood I did find that the insulation on the two wires on one of the injectors was gone because of the cover but fixed with high temp electrical tape.

I was thinking maybe EGR? :roll:

Goinig to check coils when I get some time and replace the fuel pump filter.