Well,
Seems it's one thing after another...

My truck started acting weird the other day, now it's getting kinda scary.

It won't maintain constant RPMs on the highway.

Sometimes the RPMs will bounce a little bit - other times it will downshift, go to 4500 RPMs, and ROAR with barely touching the gas!

Really running like crap.

When I stop at a light, it will sometimes stall ORthe RPMs will vary up and down.

Sometimes it will idle at 1500 RPMs, other times bounce between 500-700.

I'm becoming afraid to drive it at this point. Seems to happen after it is nice and hot.

I've tried:

1) Seafoam -LOTSA smoke. very little difference
2) clean TB with throttle body cleaner from Advance Auto Parts. no change
3) belt dressing - thought it might be slipping. no change.
4) changed to higher grade of fuel. no change.
5) checked all vaccuum lines, etc... none disconnected, no change.
6) check for codes w/ OBDII. no codes, no change.
7) no check engine light. no change.

Ordinarily I would disconnect the battery to reset the PCM, but I can't because of a unit installed in my truck will register as I have tampered with it. Can I reset the PCM by pulling the fuse?

Anybody got any ides that can help me???

 

wow that really sucks...whats in ur truck a hemi? 4.7? also my trucks rpms bounce a little when im in nuetral and still rolling for some reason...and does it stall out when its parked and you slam on the brakes?

 

Yeah, it's a 4.7.
It stalls in drive at a stop light, or in park. doesn't matter...

I just went around the block to the store and the RPMs were varying by 500. That's quite drastic.
I have to keep one foot on the brake and one on the gas to keep it from stalling.
The varying rpms on the highwayact like slippage - except that there's no slippage!
Just going along at 2000 RPMs one second - and the next, it roars up to 3000, and back down again!!!!
Its well beyond warranty - so that's not an option. Any ideas?

 

Swap out your Throttle Position Sensor and clean the Idle Air Control if you have one...both are one the throttle body. Did you remove the throttle body when you said you cleaned it? Probably not since you used belt dressing...

Oh and on that note don't use belt dressing. If you need a new belt then buy one, if it still squeaks or is loose then get anew tensioner....don't be lazy dude.

 

Also do the 4.7's have a MAF? If they do then what you're describing is a dead ringer for it...

 

Thanks for the ridicule and snap judgements, SeVeReDiStOrTiOn...
They didn't help at all.

I just replaced the belt about 1200 miles ago. I got a bit of oil on it the other day,
and I didn't want to throw it in the washing machine. I thought that it might slip because of the
oil on it. Thanks for getting the whole picture before calling me names.
I've turned more wrenches in the past 19 years, and I've earned my busted knuckles...

Yes, I removed it - new gasket, throttle body cleaner applied with a rag gently.
Cleaned the IAT sensor. Same problem.
At first it would run pretty normal when cold, now it's getting to be all the time.
Please be kind with your words... There's no need to drive people away from the forum -
Many young guys getting their hands dirty for the first time should find a nice home here...

 

the 4.7's don't have a MAF - or at least not one that I've found anywhere.

Thanks for the replies. Keep the ideas comin'!

 

well what i was getting at is it the brake booster? i know if you have a bad brake booster it will mess with the rpms and make it stall out when you slam on the brakes...just a thought

 

Not too familiar with the brake booster.
vacuum lines look good on there. other than that, not too sure...

It doesn't stall when I slam on the brakes. I does it if it's loping, and I let the idle get too low (by not tapping the gas to keep it running).

I fear that I may have to take it to the local dealer and spend LOTS of hard earned.
The dealer I bought it from is a state away. (found it on Autotrader.com).

 

I was thinking of the TPS as SeverDistortion had mentioned above.
That sounds like the next logical step.

Hey SevereDistortion... Do you know about what those parts would cost?
Have you ever had occassion to change them out?
Just trying to find out the price range. If cheap enough, I'll go that route next...