HELP! 4Runner loses power once at temp

Hi all,
I just purchased a 2000 4runner 3.4 non-cali. emission with 228K. I am having a hard time fixing the issue it's having. It will start and idle without any issue. Initially, it drives excellent without any concern at all. Once it is hot (up to full operating temp), if I turn it off for a few minutes and get back in to drive again, it will start perfectly fine but will start to cut out power really badly to the point that it will not accelerate at all, but if I give it full throttle, it will engage and take off again. The first 25-50% of throttle has no power at all. If I full throttle it enough, it appears to slightly clear up and have power at lower throttle again. I get a pending code of P0171 for system lean bank 1. Only other issue I see is the ABS light is on which, I believe, is due to broken wires down by the front wheels. Her are all the parts that have already been replaced.

Previous owner:

• ECM
• Fuel pump (unknown what brand)
• Fuel filter
• Multiple trips to the mechanic for diagnostic/repair

ME:

• MAF Denso brand
• Upstream and downstream O2 sensors Denso brand
• Cleaned throttle body
• I have plugs, coils, wires and an intake boot coming but not installed yet

I am unsure where to go with it next. The P0171 code could possibly be affected by the cracked intake boot but would it cause it to cut out power?
Would a faulty ABS system cause it to cut out?

 

Just guessing, but maybe a vacuum leak when it gets to operating temperature.

 

I'm calling a bad fuel pump, fuel filter or fuel regulator.

Since the first 2 were changed...I'd focus on the regulator.

Other things that came to mind:
bad TPS or pedal position sensor going bad when hot (or wiring)
plugged catalytic converter which if true will often idle fine but not allow acceleration

 

Initial thought is maybe leaking fuel injectors, rent a fuel pressure tester and check for pressure bleed off. You could try running a bottle of Techron & premium gas if you are seeing pressure bleeding off. Second thought is a failing TPS. Get a volt meter and find the test procedure for the 3.4. Then check for vacuum leaks, buy or rent a vacuum gauge and test all of the vacuum solenoids, find a way to smoke test the intake. Exhaust leak MAYBE but I am leaning towards leaking fuel injectors or the TPS.

When I worked in a shop one of the older mechanics always exclaimed how Toyota fuel pumps rarely fail. He had seen less than a handful of failed pumps in his career.

 

Thank you all for the input. I "may" have found the issue but am going to put a few more miles on it to confirm the repair. After speaking with a buddy...who has a buddy that is kind of a Toyota wiz, he said to check the ECT sensor. He stated that these tend to be a common issue but are often overlooked because they do not always throw a code and "appear" to be functioning correctly. Especially in my case where it was still registering the temp properly. His explanation was that sometimes, if you turn the vehicle off for a moment, of even just simply getting up to temp, the faulty sensor will tell the computer that it is back at a "cold start" and begin adding more fuel (loss of power at the lower RPM's). The system then tries to compensate for the excessive fuel by adding excessive air and throws the P0171 code for "lean". The A/F system is then just working against itself trying to balance out.

Prior to replacing the sensor, I put my scanner on it and watched the live data. While I don't fully understand the data, I do understand enough to know that both the STFT and LTFT running around the -20% range is not good. This is what started me thinking excessive fuel. The next day, I put in a new ECT sensor and hooked my scanner back up from cold start. What I found was that once the fuel trim hit closed loop (CL) both the STFT and LTFT balanced out right around the -2.3%-1.6% range at idle. And yes, I understand that the LTFT is more of an "average" reading that is calculated over longer run time. With giving some throttle, everything still came back to what I was calling the "normal range". This alone was encouraging because it was significantly better than anything I was getting before. From there, I did multiple test drives, turning the car off and on. I duplicated the things that seemed to "trigger" the symptoms before and so far it is running great.

I have read a lot of forums researching these issues but none of them ever seem to come to an actual conclusion and a clear cut resolution for their problems. After I get some more miles on it and verify if this did in fact resolve the problem, I will make sure to update this thread so that others can see what I have found. If it did not fix it, I will share that as well.

 

Back to the drawing board. After running amazing yesterday, the same issues began again today. Let it warm up at idle. Once warm, it started idling a little rough and both long and short term fuel trims dropped back to -16% to -20% at idle. Try to drive and loses all power again and won’t accelerate. Trying not to get overly frustrated with this but it’s hard not to. Nearly everything has been replaced except injectors, fuel regulator and TPS. Once my test fittings arrive, I will check fuel pressure.

 

So, the ECM thinks that it's running super rich. Pretty sure this is calculated between the upstream and downstream sensors.

https://www.youtube.com/watch?v=pIJdCZgEiys

It almost seems to mirror, this guy's issue:

https://www.youtube.com/watch?v=3RqwiVM6GUY

You run fine in open loop because the ECM isn't using the O2 sensors. When hot, it goes closed loop and your O2 sensors are wonky so the ECM goes to the max adjustment.

I would look and verify the wires on the sensors are NOT flipped. I would verify the sensors are not switched one to the other. I would verify that you have the CORRECT sensors by calling TOYOTA and requesting the part numbers for your VIN and cross reference them to the replacements on the car.

I would verify the sensors and wiring is not grounded incorrectly somehow.

 

I have verified the correct sensors, as well as upstream and down stream locations. In this vehicle, I don't believe it is possible to flip the wires, but I will triple check to be sure. I am going to inspect the wires above the pigtail for damage. I also plan to do a little checking and see if I am able to read the LAMBSE readings with my current scanner or not.

 

UPDATE: The 4runner is currently at a shop that was highly recommended to me. Unfortunately, it is costing me a little more $$$ than I have but I will figure that out. They have replaced the fuel pressure regulator as it was running 10psi too high at idle. With that resolved, they are now replacing the ECM. When they unplugged O2 sensors with the vehicle running, there was very little change and it threw no new codes. They have determined at this point that the ECM is bad and is not communicating. With the new ECM, I now have to pay a locksmith to key and program a transponder key to work with the new ECM. Long story short, new FPR, ECM and transponder key with a $1,600 bill so far. Praying this will ultimately fix the issue. Will post the outcome once repairs are complete.

 

Fingers crossed but this will be the first time someone has posted a bad ECM. They get suspected but I don't know if I remember it fixing anything. Hold off on the fob programming. It's not needed. The keys have no chip.

 

Thanks for the response. You were exactly correct. Shortly after your response, the mechanic also called me back and said there is no security system on the vehicle, so it does not need a chipped key. They are reaching back out to the manufacturer for the ECM to check if there was a programming error.

 

UPDATE: Here is a little back history of the 4 runner that may explain some of the current issue. The previous owner had rolled it, so they took the front portion of the cab from a different 4runner and welded it onto this one. "I think" they burnt up the original ECM with all the welding they did. They had it at their mechanic who stated that it needed a new ECM, so they had it replaced with a used ECM from a different vehicle. Fast forward to now, I have it at my mechanic trying to diagnose the issue once again. They determined that the ECM is not communicating correctly, so they ordered the replacement one and matched it with the numbers on the current ECM that is in it. Once the new ECM arrived and was installed, the 4runner would start and run but was still throwing codes for A/F ratio sensor....mine does not have an A/F sensor. This one is a federal emissions 4runner, so it only has two O2 sensors. After he spent quite a bit of time on the phone with the Toyota dealer and the vendor for the ECM, they determined that the last ECM that was installed was for California emissions vehicle and was installed in my federal emissions 4runner. As of now, the incorrect ECM was sent back and a proper replacement is being sent to us. I am hopeful that this will resolve the issue once and for all. Will update with the final verdict.