Intermittent RPM Drops and Stalling- TPS?

[aontkos]

I have been chasing an intermittent and seemingly random problem with my truck for a few years (2000, 3.4L, automatic transmission). It was infrequent and unpredictable enough that I've mostly ignored it, but it has become a little more predictable and I've stalled in traffic a few times, so it's time to nip it in the bud.

The problem usually occurs when the engine is warm and the air temperature is hot. It pretty much only happens when accelerating from a stop and seems the worst in stop and go traffic. When I accelerate, the RPMs will drop suddenly. It only lasts for about a second, then it returns to normal. Unfortunately, it has also stalled 2-3 times now in stop and go traffic. It will drive normal for months on end and then the problem will come back, usually after returning to stop lights after being on the interstate. It seems to only occur at low speeds and while coasting or accelerating in first gear.

I have never gotten a CEL when this occurs.

In the last few years I've replaced the following and the problem still occurs:
-IAC (OEM)
-Injectors (MotorWest Performance)
-MAF (OEM)
-Fuel Filter
-Vacuum Lines (silicone kit)
-A/F Ratio Sensor (OEM)
-Spark Plugs and Wires

I am currently at a loss, but I am leaning towards replacing the TPS. Any insight before I place an order for one? I almost feel like it's my last option!

 

[Twisted Sid]

I had something similar happen on my '99 (partially why my sister gave the 4runner to me) but it would throw a CEL for the TPS. She had the TPS changed before but with a cheap aftermarket one so i changed that out with a used OEM one and it went away for a few months but came back. Was poking around with it idling and when I moved the TPS harness, the idle would change and drop down to where it should be. Zip tied the harness up in that position and the problem went away. So I went to the junkyard and cut the TPS harness out of another 3.4 and spliced it in and the problem never came back.

 

[spartacus]

I have been chasing an intermittent and seemingly random problem with my truck for a few years (2000, 3.4L, automatic transmission). It was infrequent and unpredictable enough that I've mostly ignored it, but it has become a little more predictable and I've stalled in traffic a few times, so it's time to nip it in the bud.

The problem usually occurs when the engine is warm and the air temperature is hot. It pretty much only happens when accelerating from a stop and seems the worst in stop and go traffic. When I accelerate, the RPMs will drop suddenly. It only lasts for about a second, then it returns to normal. Unfortunately, it has also stalled 2-3 times now in stop and go traffic. It will drive normal for months on end and then the problem will come back, usually after returning to stop lights after being on the interstate. It seems to only occur at low speeds and while coasting or accelerating in first gear.

I have never gotten a CEL when this occurs.

In the last few years I've replaced the following and the problem still occurs:
-IAC (OEM)
-Injectors (MotorWest Performance)
-MAF (OEM)
-Fuel Filter
-Vacuum Lines (silicone kit)
-A/F Ratio Sensor (OEM)
-Spark Plugs and Wires

I am currently at a loss, but I am leaning towards replacing the TPS. Any insight before I place an order for one? I almost feel like it's my last option!

A new pcv valve might be a good low cost part to throw at it and see if it helps.

 

[aontkos]

I had something similar happen on my '99 but it would throw a CEL for the TPS..

Thanks for the insight! I checked out my harness last night and it seem to be in good shape.

A new pcv valve might be a good low cost part to throw at it and see if it helps.

That's cheap enough that I'll throw another one in. I'm pretty sure I replaced it about 45K miles ago, so I'm probably due for it, but I noticed the problem while that initial replacement was relatively new.

Just as an update, I decided to unplug my TPS from the harness last evening to see how it ran without it. Oddly enough, if I revved the engine with the sensor unplugged, it would stumble when it tried to idle again. The RPMS would drop in a way that is similar to what I experience in stop and go traffic. An OEM replacement is on the way. I never got a code for the old one and the resistance seemed to check out with my multimeter, but it's worth a shot...stalling in stop and go traffic on the highway sucks.

 

[aontkos]

I just wanted to post a follow-up on this thread in case it turns up in someone's search.

I came across this thread and it described my problem perfectly. The OP remedied the issue with a new evap/charcoal canister and a new crank position sensor.

I went ahead and replaced both as well, so hopefully my stalling issue is resolved. It was random enough that it could take a while to find out if the problem is truly fixed, but I am hopeful.