Engine/Transmission (1998.5 - 2002) Revving at idle or constant throttle.

[firefighter_2000]

Over the last few days I've noticed that under constant throttle I have a sort of inconsistent revving of the engine. I first noticed it going down the interstate and it felt like a split second heavy accelleration. Started watching the tach and it would jump probably 75-100 rpms like you stabbed the throttle and immediately let off. Takes about a second for it to rev and return. I tried an APPS reset and it seemed to work... until I noticed it again. It only does it when the engine is hot. My first thought is possibly the APPS going bad. Its very inconsistent. Fuel pressure is good and everything else seems normal. Any ideas?

Craig

 

[JLandry]

Craig,



Assuming the APPS has seen a lot of use (isn't new), then that'd be the first thing I'd suspect also. It can't hurt to replace just the TPS, and then worst case if the problem doesn't go away, you'll have the old one as a spare. Geno's as well as others sell them.



Another thing that can cause strange engine RPM behavior is electrical noise on the TPS circuit. An old alternator with failing diodes and/or worn brushes can cause this. As with the TPS, if you have lots of miles on your current alternator, it might be worth replacing or repairing your current one and keeping the old as an emergency spare. PM me and I can look up and send you a link to a NEW replacement alternator I found on eBay which sells for about $120. I have one on my truck and it's working great.



Lastly... and I saved this for last because I don't want to alarm you... it's possible you have a problem with the ECM or even the VP44, but obviously you'll want to rule out the inexpensive / simple stuff first.



Please keep us posted on what you find.



John L.

 

[HBarlow]

I ran an '01 325k miles and experienced numerous failed APPS modules, basically one every 45k miles, but my APPS failures always resulted in a dead pedal. I never had any wandering engine speeds, just one minute the APPS worked, the next it failed.

I would be more inclined to suspect the alternator brushes John L mentioned, or another cause.

 

[cmills]

firefighter, mine did the same thing except mine was most noticeable when the truck was cold. I replaced the APPS and that solved the problem. I'm not sure that's what your problem is but it did fix mine.

 

[FourBarR]

Did you check for codes? apps generally set a 0121 or 0122 .

 

[PatrickHansen]

Check your cam position sensor.

 

[firefighter_2000]

I'll start with those...

I kinda suspect that my ECM is starting to get tired. I've got the lazy wait to start light light already. But those other things will be the first I'll try. The alternator gauge shows normal. Dont have any codes. Hard to say. I'll keep everyone posted. In order of expense, starting with the cheapest.

Thanks

Craig

 

[barryg41]

I had something very similar to what you are seeing. It felt like the transmission was going in and out of OD very quickly. I checked the batteries and one of them was weak. I changed both. Along with putting tin foil on the black (ground) cable coming around the alternator to the passenger side battery. Then putting black tape over it.



The batteries fixed the constant throttle problem and the covering of the black cable fixed the idle problem. Electronic noise and the alternator trying to keep the battery charged was the culprits for me.



One other thing, I replaced my transmission with a DTT transmission. James Northum of Dallas installed it for me, he also put on DTT's noise suppressors.



Hope this info helps!

 

[firefighter_2000]

I have...

I have an ATS trans, and two nearly brand new optima batteries. Not really sure what this problem is.

Craig