3400 that accelerates byitself?

[jdredd]

Not a grand am, but a 2001 Pontiac Montana with the 3400... its my fathers..

Sometimes idle's perfectly and driving around, rpms are happy.. but then all of a sudden it will start to idle high and pull itself... and stays like this for days... then goes away for couple hours then starts to happen again.

Things we have done is replace all TB sensors (iac,tps,maf) and replaced the TB itself... still does it..

wiring to pcm looks "ok" ... i even replaced the PCM and flashed the pcm to latest code and still same problems... worked fine for about an hour, then rpms jump.. I even set the desired idle to be lower and still jumps up where it idles at ~1000+

it always stinks of burning coolant, and the dealer in the past has replaced intake manifold gaskets and tb+sensors twice before back in 02 or 03 ....

it was fine until early 05, and he's been putting up with it since..

Only other solution is for is to do a subframe drop on this sucker and check the engine for any busted gaskets for air leaks or something... its a PITA to do anything on this motor being shoe horned in there..

i work on 3800's mostly and hated working on my old 1990 3.1v6 and 94 dohc 3.4 ... and i know the 3100/3400 are baically same deal... just still a pain :(

[4kQuad]

for what it's worth I'm wondering about the cruse control. can you feel the gas peddle move down as the rpms climb?

Has anyone pulled the ground wire off the battery for a while then put it back on to reboot the car computer so to speak? I would think so doing the flash...??

Sorry not much help, but would love to read the fix when it is.

[jdredd]

I *think* one time we disconnected the cruise cable.... but i can tell him to pull it off and try it out..

No need for the pcm clear since i replaced the pcm and flashed it myself with my offboard adapter (i work for DHP so i have all the cool tools) :)

Only other thing I can think is throttle cable is pinched or something...

Or a vac leak somewhere down in the back somewhere where i can't see...

[rixGAphx]

Sounds a LOT like EGR problems I've had in the past, and that thing does have vac to it.
It's a royal PITA to access on a GA, and should be a Double-PITA x Eleventybillion on the Montana.

Are there any codes set in the PCM?
Even if the SES light isn't 'on', it should be storing SOME data.

Sorry, gotta go now.
I'll ponder a bit more and return.
-Rick

[jdredd]

Only PCM code it set was for the rear o2... but awhile back it did set one for "generator" .. cant remember exactly, but was basically alternator code....

I disabled the rear o2 sensor code awhile back...

Now it could possibly be alternator i guess being goofy possibly? Anyone ever ran into something like that?

If its EGR, i can just unplug it, disable it in the PCM.

[jdredd]

disconnected egr, iac, throttle and cruise cables... start the vehicle up.. idles then slowly creaps up to 1000... then slowly up again to around 1100+ , and stays there... like clock work...

put it back together.. and at first wouldnt start. did a few more times, same thing.... i then had him try and start and i kept the throttle open for a few seconds and it stayed running.... idling at about 750-800 .... shut it off.... started it again, fine this time.. idling perfect again... so how long that lasts, cause its always come back...