Experiencing some similar problems with my 1999 4runner 3.4 but also some other interesting ones. Background: My 4runner had a CEL on for a while, and one day i was driving it, the engine starting making a loud ticking sound, and needless to say, i should have stopped driving there instead of attempting to get it home. Ended up blowing up a loose spark plug. Had the mechanic tap and die new threads in, and it ran well after. I was still getting sub par mpg, around 11, and my cel was still on. So I finally decided to cough up the money to replace timing belt, water pump, and to address the CEL. $1000.00 later, they replaced rear O2 sensor, TPS, Timing belt, Water Pump, Thermostat. Drove it 2 miles from mechanic, cel came back on, and chugging at 2000-3000 rpms...but not below or above, its a manual transmission btw. Also, usually it idles around 750 rpms, now around 1500+. Codes read as insufficient coolant temp( i didn't replace coolant temp sensor, but if i unplugged it, the idle dropped back down to 750rpms, if this means anything) and i forget the other code number, but suggested toward Front O2 sensor. I bought a new denso O2 sensor for front, installed it, and managed to get light off after battery reset, but still same symptoms.....high idle, and jerking/chugging at 2000-3000 rpms... Also in the past, i have cleaned the throttle body, and had a new MAF sensor. Took it to stealership last week, and they think its the IAC. Is it possible that once the mechanic changed out the tps, O2, etc that those parts were actually masking the chugging/jerking problem, and once they were fixed, it wasnt getting the same accelerated fuel supply or whatever as before,or is that just crazy talk?...frustrated and in need of suggestions. thanks in advance.

 

You've replaced nearly everything that I could think might cause this problem.

Here's a writeup on how to clean the IAC valve:

https://www.yotatech.com/forums/f123...ac-pics-92286/

After I did my motor swap, I had similar symptoms and swapping out the IAC valve did the trick.

Taking apart the IAC valve and cleaning it is very simple, but be sure to get a very good fitting screwdriver with good leverage because the screws are tight and you don't want to strip them. Other than that, as you'll see in that thread, it comes right apart and cleans up easily with some brake cleaner or the like. Also, if you remove the throttle body/IAC valve to do this, MAKE SURE YOU HOOK UP THE LINES CORRECTLY WHEN YOU REINSTALL! One of those lines is a vacuum line and the other is a coolant line. If you run coolant into your engine you will kill your motor. I know from experience.

I'd bet, with all you've done already, this is your issue. Best of luck to ya!

 

thanks for the quick reply.
Tonight i spent a few hours on my rig, changing out the coolant temp sensor, which once you have the timing belt cover off, and move the fuel jumper line, its pretty straight forward. After putting a new one in, getting it all back together, my 4runner still had the same symptoms, even after warm up and a couple mile drive. So, i opened the hood again, took off the throttle body, the IAC, and cleaned both with throttle body cleaner. It was more of a thicker grease and dirt build up than carbon, but tried my best to get it clean. I will upload a pic when i get a chance, but it seemed like the IAC valve didnt completely close all the way when i turned it...there was a 1/8'"-1/16" gap. After cleaning it , it seemed to rotate must more freely but still had the space/gap. I placed it back on the 4runner, and still same systems.....by the way, stealership told me that the high idle was due to a bad IAC and shuttering at 2000-3000 rpms was due to a poor charged battery. I replaced the battery, and still the same problem, but before i drop $200 on a New IAC, i wanna make sure im headed in the right path. still no cel.
As i was thinking, could it be possible that the mechanic who put the new timing belt on, perhaps put it on wrong, and the timing is off? would that cause this problem,? i fig no since that would cause timing problems all around, and not just at idle and 2000-3000 rpms......this is just getting so frustrating.

 

Thinking out loud, I am by no means a mechanic or even play one on tv.......
Search knock sensor(s), more specifically, knock sensor wiring. Unfortunately that's not a straight forward fix and you can't just look and see because they are in the valley under the intake manifold. The 2 sensors are muy expensive, but the wiring is not. Just something to think about.

 

Where are you located? If you're near me, you can swap over my extra throttle body and TPS and see if that makes a difference. I feel your pain, you've done a lot to tackle the problem. At the very least, feel good that you've replaced a lot of little stuff that could cause problems in the future.

Last ditch suggestion: Loose/leaking vacuum line?

 

@habanero:I will look more into the knock sensor/wiring
@98sr54runner: I am located in PA, so thats kinda a stretch. As i forgot to say, my D.D is another 1999 green 4runner, 3.4 sport edition automatic. I actually worked on both that night, but luckily just a oil change in my D.D. I did think about ripping the TPS off it and placing it on my 1999 silver sr5 4runner standard 3.4 with the problems. the only reason i didnt was it was already 1am by that time. Hopefully this week ill have some time, and try a swap. I believe that both 4runners, since they have the same engine, everything should match up. does it matter if they have two different transmission...i.e. vents,hoses, cables to throttle body? Also im going to look into the vacuum lines.

 

also, i was thinking maybe a new IAC would correct the high idle, but the shuttering at the 2000-3000 rpms might be a fuel issue. the 4runner sat for a 8months to a year when i was making new rocker panels, building a off road bumper etc. so i was thinking maybe a lot of rust or sediment in the gas tank was sucked up into the filter, and possible since the high idle masks the lack on fuel on a low idle, but once you get to a ratio of air to fuel at 2000 rpms theirs not enough getting through the filter fast enough, and then when you stomp on it above 3000rpms its forcing it...idk, its possible, maybe not logical. but hey fig i can switch out a $15 fuel filter if it will help.

 

It does not matter what transmission you have. A 5VZFE is a 5VZFE and for the most part, you should be able to interchange parts freely. The throttle body/TPS should definitely be interchangeable. It absolutely could be a fuel issue. I'm not sure about the high idle, but the chugging at higher RPMs could definitely be a fuel issue. Last time my rig did that, it was an injector, but I had a code clearly telling me cylinder misfire and that's not the CEL you're getting. Try a new fuel filter, it's cheap, but I doubt that's the problem since they're supposed to be a lifetime part.

Swap over your other TB and TPS and check your vacuum lines and let us know if that makes a difference. Your symptoms sound just like mine when the TPS was gunked.

 

98sr54runner- would it matter if the mechanic put on a aftermarket or cheapo tps rather than a oem from the dealer/toyota parts website? i know certain spark plugs make a huge diff when coming to that issue, but wasnt sure about a sensor like that.

 

the only injector cleaner i have used in it over the years prior was BG44K. Also i noticed that when the engine was clearly warm in the dash gauge, the upper radiator hose was rock solid, suggesting the thermostat still was not opening? That along with the tps was replaced when i dropped all the money on timing belt, etc.

 

@98sr54runner....took it back into dealership after i changed out what they told me was wrong, IAC and bad battery...still no fix. today they informed me that i need a new throttle body because the throttle rod is bent or worn, and it wasnt closing completely. They want $1000. for a new one, im gonna look around junk yards and see what i can come up with. Also check the forum to see if anyone is selling one. would that cause the stuttering at 2000-3000 rpms? hmm

 

Don't waste your time... do this instead: https://www.yotatech.com/forums/f2/m...-cured-258318/

 

okay, this might sound like a dumb question, but if i go to place a small washer where you describe, how do i go about doing that procedure? Isnt the trottle under tension by the spring? etc

 

The throttle cables that are under tension can easily be removed from the throttle body. The end of the cable has a little metal shaft on it that you can push out of the holes in the wheels on the TB to disconnect them. It's very easy and you'll see what I'm talking about when you get under the hood. The part that you take off to get the washer there is what you will disconnect the cables from.

 

I'm having the EXACT same problem! It started with a plug blowing out, just like your describing... It's been down hill since. It's a 98 4Runner with 250k miles, stick, 3.4l, etc. Have you had any luck? This &$@? is KILLING ME!

 

@russsharp,,,,any luck on your end??