well it is like this, it is my friends truck and we will be driving for about 10-30 min and it will be fine. then all of a sudden it is like he lets off of the throt and and the rpms drop to ~800 then it revs up to ~1700 rpm then lets off again and continues like this for about 10-20 min. while all of this bouncing in rpms is going on he has the throt depressed (opened) in one stationary spot. the truck is a 94 3.0 4x4. if we pull over and stop for a while it seems to go away just as sudden as it starts. it does not matter if he puts it in 1st or 5th gear it acts like it is hitting a rev limiter at 1700 rpm. i have replaced spark plugs, sp wires, dist cap and rotor, fuel filter, air filter, checked timming, checked tps and vafm. i am stumped???? if you have any sug please

 

over heating???

 

sticky thorttle cable or the thorttle body is not closeing all the way

 

clean your MAF sensor thoroughly.

 

remember, these have a dash pot so the throttle doesn't close right away when you let off the gas.

 

thanks for the replys i am going to change the coolant and thermo this week, the temp sensor is reading normal so i will also do a system flush. i will also look at the maf (mas air flow sensor right?) the weird thing is it just happens while driving down the road with the throt depressed at the same level, it just all of a sudden starts doing it?? also to clean the dash pot is that just cleaning out the filter? thanks again, harley

 

Throttle Position Sensor?
Idle Air Control Servo?

 

maybe clutch is slipping

 

I dont remember they symotoms, but I had a malfunctions temp sensor that screwed with the ECU but looked normal on the gauge. I wouldnt rule it out...but it sounds more like a throttle cable sticking, this happened in my 92 after it sat for 6 months while I was at flight school.

 

I had a hell of a time trying to decipher your first post. Let me get this straight: You'll be driving down the road at say 3k rpm, all of a sudden the rpms will just drop down into the 1k's? Is that is an accurate interpretation? Because I think you've confused everyone. Or maybe I'm just the one who's confused.

 

There is no MAF on this engine.

 

O, the lost art of proper sentence construction.

 

I am sorry about confusing some of you but it is hard for me to type when i am frustrated. The symptoms of it are: driving down the road, motor cuts out and rpms drop down to around 800 rpms (loss of power like if you take your foot off of the gas), then soon as it hits ~800 rpms it shoots back up to around 1700 rpms, as the motor rpms go up to the higher rpms the truck acts as if you pop the clutch (a surge of power, a bounce if you will), when it hits ~1700 rpms power cuts out and it dives back down to ~800 rpms as if he were to let off of the gas while normal driving. Then as soon as the problem first started, the problem ends and it is back to a normal like a well working motor. If he lets off of the gas when it is doing this it will stay at idle rpms and not bounce. As soon as he tries to give it some gas to raise the rpms to drive off it will go back to the bouncing thing where it will rev to ~1700 rpms and back down then back up. The motor acts normal if the throt is closed (petal not depressed at all) while this problem is going on. Hope this helps some more.

 

check your cap & rotor

 

I dont think its the MAF, but there is no MAF on this engine?

Has he messed with the TPS lately?

 

there is a VAFM. If your wires are loose, corroded or you have a vaccumm leak in the system you could be having these issues

 

also we have replace all the vac lines, also the rotor and cap. i will check the wires to the vafm, i have checked the vafm and it is within tollerance. i also checked the tps via the "how to check tps" link. has anyone had their pick-up coil slowly go out? i have heard that it can have this kind of symptoms. thx

 

I had a loose ground at the coil one time on a 22RE. Dropped and raised throttle at "random" times. The random times turned out to be when I hit bumps, and the ground would fail for a second.

Maybe your bad luck is something this simple?

 

i did a coolant flush and thermo replacement, cleaned throt body, intake maniflod (upper half) and all of the tubes and the fuel injector on the back(pass side) of the manifold. i am going to try and re-ground some of the old grounds and see if it helps any. i am going to try to take a video clip of it if it acts up again so you can see kind of what i am talking about. thanks

 

This sounds remotely familiar so I'll swing for the fences and say to start searching for info on "limp mode" on 3.0 motors. I can't remember if this is caused by o2 sensors, temp sensors or auto tranny problems, but I do remember it being very much like you are describing and the timing would be right for the o2s to be up to operating temperature.
I started to search, but I'm on dialup on an antique computer and it's late
Just an opinion.