I have a 1990 4Runner with a 3.4 V6 swap in it. I have been having a hesitation issue I can't seem to get resolved. I have tried the following:

Replaced fuel filter
Cleaned mass air flow sensor
Cleaned throttle body
Replaced spark plugs with NGK's
New plug wires
Inspected all 3 coil packs


When I am driving if I keep the throttle below 25% it is smooth as a whistle. Between 25% - 75% it starts hesitating. The closer you get to 75% it gets worse. If you punch it and have the throttle at 100% WOT it comes alive and is fine. This issue only shows up when the motor is under some kind of load like accelerating hard in 2nd gear or going up a steep grade. My gut feeling tells me this is a TPS (throttle position sensor) issue although there is no check engine light on.

I used my ohm meter an conducted the test for the TPS. Everything was in spec except for the "fully closed" IDL - E2 which should be less than 0.5 and mine was 6.5. The chart says to apply vacuum but I had not way of doing that so I am not sure if that is why the one setting was off. If my measurements are true could this be my problem?

I also tried turning the throttle body and watched the the numbers slowly increase to see if there were any shorts or dead spots but did not see anything.

Any ideas??

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Not sure where you got the TPS check but it does not look like a 3.4

Is it causing the MIL to trip are you getting the P0121 code?? Or any other codes??

The Diagnostics section in the FSM is great for these 3.4 engines along with being able to pull the codes.

 

I got it off of Yotatech and it said it was for a 3.4. As for codes the check engine light is not on. I ran a OBDII scanner anyway and there were no new codes or stored codes

 

Did you do the swap yourself? Did you even hook up your diagnostic port or MIL? Sounds like your open loop is fine. You're having problems in closed loop. So diagnose your o2 sensors, TPS, MAF, cam and crank sensors, and check really good for vacuum leaks. Wyoming9 is right about the FSM having a pretty good diagnostic section.

 

No Yota Masters in Corona, CA did the swap years ago. The diagnostic port works fine and I had a check engine light come on in the past for something else. As for my O2 sensors, I have done test while I am driving and can see them come in and out of closed and open loops depending on the conditions. I just downloaded the factory FSM on the 5VZ-FE engine and I am reading through it for more info to help diagnose the problem. I am still leaning on the TPS.

 

Is it possible your throttle cable is on the way out causing all these problems.

If your TPS was not talking to the ECM it would have tripped the MIL ..You have changed your air filter ??

Check your fuel pressure??

Made sure the throttle body is clean linkage lubed at every oil change ??



From your description it has been happening for awhile ??

Just how did it start ??