91 22re pickup, only stumbles at certain rpm, idk exact rpm because of no tach, but very slightly above idle it cuts out and stumbles as long as you hold it there, but runs fine above and idles fine.. I have a Toyota tech for 40 years stumped on this one. Already tried basic plug, wires, cap, rotor button, fuel filter, timing is good( mechanic told me) egr is fines, o2 sensor is new. Tried another used afm. Checked for leaks. Unplugged tps and no difference. Doesn't matter if it's warm or cold out. Or how warm engine is. Thinking about trying a new ecu? Just got the truck couple months ago, it ran like junk when I bought it. I can't even drive it in public haha. I believe it was a beater before I bought it, so could have gotten ecu wet? Just my idea.

 

And could a tps get a dead zone? Would like to try adjusting before I go out and buy a new ecu. could it be a bad ground wire?

 

nobody?

 

mine does that too. I think its just the TPS. Most of the wear is on the beginning of the resistor in the tps, so its likely that the bucking could come from being worn out. Let me know if that solves it. The only other thing that I could think of is that the maf is bad...which sucks because that is $$$$$$$$$$$.

 

Thanks for the input duffdog, I picked up an multimeter last night I'm Gunna try and test it out sometime this week. I already tried a used maf from a junkyard and no luck. Blehh. I'll let you know how it goes

 

If unplugging the TPS doesn't make a difference, it's not the problem.

These trucks use a VAFM (vane/volume airflow meter) rather than a MAF.

Could be a lot of different things. My advice would be to check for codes and start testing sensors, fuel pressure, check vacuum lines, etc. etc..

 

You make a very good point bmcel. Guess I didn't think it thru. The truck isn't throwing any codes, and could the fuel pressure be a problem if it's only stumbling in a certain throttle speed??? Hmm.

 

Failing fuel pressure regulators can cause similar symptoms. Also note that just because the CEL isn't on doesn't mean there aren't stored codes.

What brand plug wires did you use?

 

I used autolite professional series plug wires. I went cheap not thinking it would make much of a difference till I did research. And when I unscrew my gas cap, I have TONS of pressure, I always wondered why. Would that also be a cause of a bad fuel pressure regulator?? I believe my mechanic (sad I know) checked for codes and none showed up. That's why he was thinking it could be the ecu. Btw I appreciate the help!

 

Went to the local auto parts store and they didn't have a fuel pressure gauge. How is this possible!

 

Does it stumble underload at this rpm or just sitting still under no load? I would have suspected the egr valve opening too soon upon accel which is very common on these trucks. Unplug EGR vacuum hose and drive? Change?

If the issue is not EGR related then i would suspect a signal fault at that RPM and a drop either in fuel or spark.

Faulty igntion coil can cause this.
Ignitor signal?
Pick-up coil in distributor?
Could very well be a Computer fault.
No trouble codes stored?
TPS being faulty is possible.

 

Alright.. Well, just took her round the 4 mile loop with the vacuum hose from the EGR unplugged. (top hose correct?) and no difference. I thought it helped a little at first but I was probably just wishing. And YES it does stumble sitting still or driving. And I've come to conclusion it's not the tsp, thanks to BMcEL. And no there are no stored codes :/

 

Looked at my ignition coil, and it looks brand spankin' new. I had somebody look at it and they said it looked fine. There was sparks jumping all over the front of it but I haven't noticed it in a while, think it was just a loose wire.

 

Alright blowin up my thread here. But I found a lead on my problem!!! 4 months of random guesses and I've finally made progress. I pulled off a vacuum hose from the Top of the throttle body( closest hose to the E in efi) and wallah no more stumbling!! Now I'm lost again haha

 

This right here could very well be your problem. At no time should you see any sparks or arcing on the coil, if you are seeing this then the coil is bad.
Sometimes the coil can get very small hair line cracks in it that you might not be able to see but its enough for the voltage to get through and ground out, and this would cause the problem your having now. Coils are cheap, and it would be a good idea to replace it.

 

It doesn't do that anymore. I just had to pull off the hose from the charcoal canister (purge hose) from the TB and it solved my problem! Now I gotta take a look inside my canister and try to unplug it or something. Also.. I have constant dripping coming out of the bottom hose of the charcoal canister that I believe is supposed to suck in air? Some sort of breather hose I guess.

 

did you fix the problem? I'm curious what solved it.

 

Yuhhp. The hose closest to the cab on the throttle body. I just unplugged it. Runs mint now. So I guess I haven't solved it yet, just... Bypassed it. I think a hose is switched with another from the charcoal canister which was giving it my problem