Odd lack of acceleration '01 4x4

No, that is just a 3-way connector. The check valve looks like a little filter. You can see in this photo (black with an orange stripe).

 

I had the same problem. It was the crank gear. timing belt showed fine, but the timing was not correct. also did the coils, wires, plugs, and injectors prior to finding this to be the problem. All power was restored. So for less in depth analysis, but the problem sounds incredibly smilar

 

I do not have that valve. I have a plain vacuum hose there instead. The rest of my EGR setup looks the same as the pic.

Thanks for the info. In your case, did the problem change or go away when the engine was warmed up? If I had a mechanical problem I would think it would be persistent, but the fact that my problem is less noticeable with a warm engine makes me wonder if it is sensor related.

 

So according to this diagram I found of my truck, the check valve seems to be an optional part. The asteric next to the hose footnotes to "MTM", while the alternate config with the check valve is "ATM". Manual vs Auto tranny or something else? If thats the case then im missing the valve.

 

Thats the impression that I had, from my 1999 FSM diagrams, that the check valve is for automatics. Don't understand why its needed, though.

If you know of someone with a Toyota with automatic (any Toyota of the same age, not just Tacoma), you could temporarily swap theirs in to see if it made any difference.

 

With a auto and TBI, you hold the throttle body open at a "steady state", as the trans shift gears,,and your vacuum stays constant for the most part.

With a manual trans, you dump the throttle closed (high vacuum), shove the clutch in and change gears, then back on the throttle. A constant vacuum fluctuation. My 99 5 speed manual does not have that orange ringed valve.

 

Did anyone find a solution to the issue, I've got the same 01 3rz with a 5-spd. Swapped a motor 8 months ago from same year and spec'd truck. Now I have the same mileage as 'jacket' and right after 2500 rpm the truck comes back to life. Cleaned the MAF, tested TPS, no idea

 

Did you change your fuel filter???

Filters are an annual replacement item that gets neglected and can clog up. Mine was bad and when I changed it, I can feel the improvement.

 

No I haven't. But how would that affect the 2,500 rpm mark on the acceleration?

 

Could be clogged and starving for gas at higher RMP when more gas gets put into the mix.

It's a cheap fix/peace of mind to close of the list of possible things.

 

I agree, cheap part. But I'm 99% is electrical or sensor related as fuel ratio would affect the entire range of acceleration. Exactly like the original post, acceleration picks up again when the revs go past 2500 rpm. Its even more odd that is most noticeable happening in second gear. Tests on the TPS came our perfectly, ran a digital sweep across it, no issues. Will probably be disassembling the throttle body for cleaning soon.

 

I never found a solution to the problem. I did discover that it seems to be related to temperature in some way. The problem is at its worst when the engine is cold, and it almost is non existent with a hot engine.

I agree it is likely a sensor or ECU issue, but I have checked all the sensors I thought could be causing it.

 

Did you clean and inspect the MAF, throttle position sensor and the throttle body?

If not try starting there. Next plugs, wires and check the coil packs to make sure they are good.

Do you have a FSM?

 

Not sure this relates to your issue Jacket, but I removed my KNN and the truck is much happier. The MAF is clean and looking good. This seems to have cleared up the majority of the issue, I have to give the computer some time to relearn the airflow. If the problem persists I'll pull the throttle body, clean it, and work down from there. Also noticed an issue with vacuum pressure off the throttle body, 3rd hose from the right has no pressure at idle or 3500rpm, related? No idea. Just taking one piece at a time so not to confuse which fix solved the problem.

Similar to your situation Jacket, it typically only occurs when the engine is 'cold' and most prominently in 2nd gear. I will update in the next week or two and keep this topic alive, hopefully we will find a solution.

 

Try some sea foam. What about the cat? A clogged cat sometimes doesn't throw a code. If it's clogged either replace it or gut it and use a URD o2 simulator.

 

Clogged cat would have little to no power, this doesn't sound like that. However, you can't rule it out.

 

Unless the cat was changed in the first 100k on the truck it has around 215k on it right now. It could be a part of the issue, but I need to make sure its not simply throttle body before dumping $1k into a new CA legal cat. From everything I've read about Seafoam it would most likely kill my cat at this point anyway, gonna hold off on that for now. This motor has the same mileage as Jackets, as I swapped to a same year motor in January. So I'm leaning towards electrical issues at this point.

 

Knock sensor would pull timing, if it "thinks" it is getting a out of range reading from a cold engine. Motor is making more "noise" when it is cold. A bad(or going bad) sensor and just a bit of inaudible cold engine piston slap could cause a problem.

 

Wouldn't that throw a code though?

 

One would think that. Worked on vehicles that didn't due to whatever the reason might be.