Hi all. I’m new to the forum, stumbled across it while doing hours of research while trying to find an answer to my truck problem that has been going on for the past 6000 miles or so. I have a 2001 Toyota 4-Runner, 3.4 engine. I am hoping that maybe I could get some ideas/suggestions of what to check to finally figure out what my 4runners problem might be. Toyota can’t figure it out and their resolve is to keep replacing parts till it is fixed.
Anyway, following is my problem, and I apologize for the long writing, just wanted to be as thorough as possible.
Truck idles fine and never shuts down on me. From a stopped position I press the gas and my truck goes nowhere. I can press the pedal all the way down and the truck just sits there, no rev, no nothing. If I let go of the pedal once or twice and press again, it takes off like normal. Then while driving(moving), I give it gas to keep the mph up and it does the same, I have to depress and press the pedal a couple times to get it to continue. It feels like it is out of gas, then takes off and runs well. If I set my cruise it gets even worse, it will hesitate and feel like if I am slightly pressing my brake then giving gas, and just jerks and revs causing me to disengage the cruise to get back to normal. It seems to do ok on the highway at high speeds once I set the cruise around 78mph, but as soon as I get off the highway the problem starts again.
This problem is not consistent and does not happen every time I drive the car. Toyota has yet to feel this hesitation or whatever the problem is because I have not been able to get it to do it on a test drive. I tried my best to explain it but they can’t seem to find what it is. Below is what has been done to the car so far.
At 88,843 miles I had my timing belt replaced, also the water pump. A few days after this is when the problem started. I’m not sure if it’s related or just coincidence, Toyota doesn’t think so. Also, not long after this the engine light came on and shortly the VSC and TRAC lights. The dealer the computer stored a code for a bad Air Fuel Sensor. They told me the only thing this would cause was bad gas mileage but not the problem I was having. I did not change the sensor at this time. After the dealer visit I tried Techroline, didn't help.
At 89,837 miles I had the dealer replace the spark plugs on a friends suggestion, didn’t help either, I still have the problem. At this point my friend tried a treatment of Stabil. Stabil fixed the problem, it was gone. But, three or four weeks later it began again.
At 93,928 miles I had the Induction service done at Toyota. Had I known then what that consisted of I probably would have attempted it myself. After the induction service the problem was gone again (for approx 2000 miles).
In the meantime when I thought it was fixed for good, at 95,422 I had the Air Fuel Sensor replaced (when the lights began coming on intermittently again). I mentioned that the car seemed ok so far but one day I had felt a slight hesitation, but only one time. They told me it was probably just a hiccup.
About 2000 miles after the Induction service the problem began once again. Took it back to Toyota and this time spoke with the mechanic to tell him exactly what the car seemed to be doing. After our conversation he decided to check the fuel pressure. He came back saying he was almost sure it was a bad “Fuel Pressure Regulator”, but, he had only see a drop in pressure one time and could not duplicate it again. He took me back to show me how he was testing it with a gauge, but he tried and still couldn’t get it to drop pressure again. He also checked the computer for codes, there were none. Toyota ordered the regulator and I would be back tomorrow morning for them to replace it. When I got home that day I began thinking, if it was the regulator why would it go away for awhile after the Stabil and then after the induction throttle cleaning, why wouldn’t it be bad all the time if it was the regulator?
I brought this up to the mechanic in the morning and asked what else he thought it could be and what else he could check. I also asked about the fuel filter and he said that was doubtful, that Toyota filters were more for safety than anything and are hardly ever changed. This time he came back with MAF sensor in hand and showed me how dirty it was. He cleaned it and I was off once again to see the results. (I don’t see why that is not part of the Induction service, but what do I know).
Drove about 45 city miles the next day and didn’t feel anything, day after that it happened again. Now having more information about what could go wrong with the fuel system I decided to go do some research, and while putting in my symptoms came up with all kinds of stuff on throttle cleaning, MAF sensor cleaning, etc. I also checked on symptoms of a bad Fuel Pressure Regulator but they don’t seem to really match what I have/feel while driving.
I still have my problem and don’t know what else to do but have the regulator changed. I asked Toyota if it wasn’t the regulator, then what? and they said “they don’t know”. I don’t know what else to do and really can’t afford to spend another $250-300 and still continue with this problem.
Any ideas? Could the regulator be bad even though he can’t get the drop in pressure to duplicate again? Why would it be ok for a while after the Stabil treatment and then again after the induction service but come back again after a couple thousand miles each instance? Is it possible that the treatment and cleaning help the regulator for awhile so it works ok then worsens again?
Please help if you can, it will be greatly appreciated. Thanks, Arlene
My guess since you already replaced the air/fuel sensor and cleaned the MAF is the throttle position sensor or the ECM (computer) itself. Your 01 is fly by wire so the computer controls the throttle cable I believe. Just guesses of course... I don't remember reading of these symptoms before. Hesitation off start is usually a MAF issue but hesitation while going down the road like you describe is not too common.
Thanks for the guesses, anything I can use is good. I will be at Toyota tomorrow morning and they are going to clean the throttle again. I will ask them to check on the throttle position sensor also. ECM? is this the module that actually gives out the codes?
Went to dealer this morning and spoke to mechanic again. I asked about the TPS and also if something could be happening when I use the cruise control (which I use pretty much all the time). He took the truck for a ride and actully felt the problem this time (finally). He now says it is the throttle body and it needs replacement. I asked about the sensor and he said the whole body needs replacement. Any thoughts/advice on that? Expensive, they are trying to find me a used one. I have 95,000 miles on my truck. I'm afraid they will tell me I need a new ECU after this.
The Factory Service Manual for your year (and 02, both elec throttle control) says if the TPS is bad to replace the whole throttle body. I'm not sure why or if there are other issues I'm not aware of. I've read other discussions on this before but could not find the threads.
He has the same year and symptoms you have and it sounds like he was going to replace his TPS. He never came back and said it worked or not...?
I did look up your year truck at Autozone's site and they list a TPS for $53 so I would spend that before replacing a whole throttle body. If it comes to that I would get one from a junk yard. TPS's don't go out on 4runners that often so this is just bad luck for you...
Are you kidding, I'm thankful for any input at this point, I have had this problem for months now. I ran across a couple things on throttle body or sensor replacement today too, but nothing really useful. Pretty much my same question, why does it have to be the whole body. I'm just weary because first they were almost sure it was the regulator, now they are almost sure it needs a throttle bottle. On the link you sent I didn't understand much but my mechanic did have some kind of electronic meter attached that showed a 5.5, I can't remember what he told me it should show, but I asked if the sensor could be bad and he said it needed the body changed.
Here is a test for the TPS. As veiwing from looking at the intake of the Throttle Body it will be the upper left plug.
Pull the plug and read the resistance on the pins at the Throttle Body. The pins to read VC and E2. The resistance should be !.2-3.2K ohms. @ 20C or (68 F) The factory manual does say to replace the whole Throttle Body. But it appears that the sensor can be replaced as kball says.
Keep in mind there are 3 things on the Throttle Body that can go haywire. 1) TPS, 2) Throttle Valve motor and 3) Accelerator Position sensor.
Also there is a sensor on the Accelerator pedal that sends a signal to the Accelerator sensor on the Throtlle Body. So there could be an issue there also. Just needs some trouble shooting to figure which one is at fault. There are tests for the other parts on the Throttle Body but you can start with the TPS. A Toyota mechanic should be able to figure these things out, he has all the books that are available to do these tests but for him it is easier to R&R and get it out of the shop. In most cases Toyota does not like to trouble shoot as it costs lots of time and money and people don't like to spend that kind of money to have them do that and they know that so they usually just throw parts at it unless they really know the system and know how to pin point your symptoms. You have to remember they work on all kinds of models and it is hard to remember all the systems. Hope this helps. This is also just my opinion and I'm not trying to bash anyone. Just trying to help.
kball - jetwhine, thank you both.
I wish I could check on this stuff myself, I don't do much more than my oil change, fluid, fuses, etc. Too scared to take anything apart and either break it or put it back wrong. I need a hands on teacher, lol. I am learning a bit with this experience though, thanks to you guys and reading other forums. I never even knew there were so many sensors. Seems like so much could go wrong, so many things to check, and no, dealers do not like to check on small stuff, they are part changers. I haven't been anywhere else yet because I already have money invested in Toyota. Also, the service mgr does try to work with me, I've known him a long time. I don't even know of a decent shop around here anyway. I will mention checking the Accelerator Position sensor and the one on the pedal when I go back. I believe what he checked was the TPS, that is where it was showing 5.5 on the meter he showed me, but I don't think he checked anything else except to see if there were any codes, which there wasn't. I asked when he showed me the meter if that could be the TPS and he told me it was probably a worn geartooth in the motor of the throttle body. I will bring the TPS question up again too. Is it true that this sensor many also need cleaning like the MAF sensor? I read something on that somewhere too. I'm not too fond of using a used part either, what if it is not any better than mine.
That is the chance you take on used parts. If the resistance is off as indicated then that will cause a problem. Like most things in your rig as far as sensors are concerned, if it is sending a signal that is wrong the computer does not know that. It is happy with the wrong signal. The only way the computer can send an error message is when the sensor quites all together. That is why the resistence checks are important. Those readings can tell you when the sensor is out of tolorence which the computer does not know. Hope this sheds more light on your issue.
I asked when he showed me the meter if that could be the TPS and he told me it was probably a worn geartooth in the motor of the throttle body. I will bring the TPS question up again too. Is it true that this sensor many also need cleaning like the MAF sensor? I read something on that somewhere too. I'm not too fond of using a used part either, what if it is not any better than mine.
If it was a worn geartooth I would think the symptoms could be repeated on command every time you accelerated to a certain point. Your problem comes and goes as your first post said you thought it was "fixed for good" but then came back. This tells me it's a sensor going out.
From what I know (which isn't a lot ) You can not clean TPS sensors. I think if you took it apart you would wreck it. I've never heard of anyone trying that.
Used parts are a gamble like Jetwhine said but... they are a lot cheaper too. Honestly from all the searching I've done for this thread it doesn't appear like this is a very common problem. Especially with your low miles. I think a used part would be an okay investment but before doing that I would find someone to change just the TPS for you.
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Hesitation on take off and while driving
) You can not clean TPS sensors. I think if you took it apart you would wreck it. I've never heard of anyone trying that.
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