Fast Idle Problem + P0120 – SOLVED!

I just wanted to share my recent experience with the intake system of my 2001 V6, since many have tackled the problem differently with varied results. My Tacoma has 195,000 miles and sees a decent amount of off-road in Death Valley and Baja California.

I had experimented with a K&N air filter a year ago and went back to stock after noticing that the fine dust common in the places I wheel was getting past the filter. Recently, I’d been getting the P0120 CEL almost every time I started the truck and it would come back within a few miles of clearing it. Also, the idle was high – settling around 1000-1200 RPM when warm.

So, armed with all the fine information gleaned from this and other Tacoma sites, I decided to start with cleaning the MAF sensor. It was a little coated with dust and came out very clean using the CRC MAF cleaner. Unfortunately this didn’t have any effect on the problem.

Next, I removed the intake duct and throttle body. I put tape over the opening behind the throttle body just in case. Using the CRC Throttle Body Cleaner and a toothbrush, I thoroughly (but carefully) scrubbed the inside of the throttle body, butterfly plate and all the interior surfaces. There was quite a bit of blackened crud in front of and behind the butterfly. I made sure to clean the ports that go down into the idle air controller (IAC). I removed the IAC and cleaned out the recess where the movable louver turns. To really clean this part completely, I found it necessary to remove the two sealed screws on the IAC and spray cleaner through the metal tube leading into the recess and gently turned the mechanism back and forth while I cleaned it. There was a lot of grime in there. I could see that if you simply sprayed cleaner into the intake without removing it, it would just drip crud into the IAC. I did not remove the other 2 smaller screws on the other side of the IAC holding down the translucent plate

As I was reinstalling the rubber gasket on the underside of the throttle body (I reused both the rubber and metal gaskets), I noticed that the outer casting around the gasket on the underside of the throttle body had a void or was broken, allowing coolant to seep under part of the mating surfaces but it didn’t appear to go too far - a definite manufacturing defect. I made sure to use a gasket sealant and built it up around the void to hopefully solve that problem.

I made sure to remove the throttle position sensor and cleaned the electrical contacts before reinstalling it. I also used a big long brush to clean the inside of the plastic intake duct and then reassembled the throttle body, let it dry and put it all back together. After starting, the idle seemed to be stuck at around 2200RPM! I drove around for about 12 miles and cold or warm it was idling way to fast. So I cleared any pending codes and disconnected the battery overnight to reset the engine management function. In the morning, I was very happy to see the idle go to about 1200RPM cold and settle down to spec after driving around for a day or so. After a week, the P0120 (Throttle Position Sensor Malfunction) has not returned and the smoothness and drivability of my Tacoma is much improved.

So that’s about it. I didn’t have to replace any sensors or other parts. For me, it was just a matter of carefully and thoroughly cleaning the intake, throttle body, attached sensors and any moving parts. I would take care to spray any stubborn fasteners with WD-40 and wait for it to penetrate. I would also recommend using the MAF and Throttle Body cleaners outside. You definitely don’t want to breathe that stuff.

It wasn’t hard, and if you take your time and don’t force anything, it’s well worth the effort!

 

Thanks for sharing. I need to do the same thing. Off topic now; Did you buy yours new, or were there previous owners? Have you had any other problems? Have you ever seafoamed it? Speaking of the K&N, had you ever tried the wrap they make for it?

I'm full of questions, feel free to ignore me...

 

maybe i can help with some of this. as far as cold air kits and K&N it is the biggest pain in the ass mod you can do. I put the Steeda cold air kit (joke) on my mustang in 2003. up to 15hp increase, bullshit. it really is a hot air intake and cleaning that filter and oiling it is a pain, and a little too much oil and there goes your MAF sensor.
yes i do the seafoam treatment. same arguments about this when I bought my mustang in 2003. the ford 4.6 is also prone to carbon buildup and it helps. I would do one can in the spring for the throttle body, one can in gas and one can when i changed the oil. and never had any trouble. the focus of some arguments were running high test fouls up the motor and the 10% ethanol in gas, and mine was used got her last fall, no trouble at all.

 

Yes, it was one of the few easy fixes I've run across . . . I'm just trying to give back. I've saved so much time and $ checking out these and the KLR650 forums for my bike that I had to share my positive experience doing this project.

I did buy the truck used in 2009 with 163K on the clock. The PO said he never off-roaded it and I believe him, as I had to show him how the 4WD and rear diff lock worked when I test drove it. He didn't even know about the diff lock or what it was for. Just the kind of PO I was looking for! He was the original owner and judging by the pitted windshield, he had put a lot of hwy miles on it. It needed a new clutch and transmission to transfer case seals which wasn't cheap but I had budgeted for that.

Other problems? I would say that the general build quality is definitely not up to the level of the 1st gen (1989) 4Runner I had. When I drilled the frame to install an airspring rear suspension, I was shocked at how soft the metal was. I've never Seafoamed it. I think I got a power bump with the K&N and I kinda liked the sucking sound when I gave it the gas, but after seeing the dust behind the filter I nixed it. Never tried the wrap. After years of wheeling and motorcycling, I'm definitely thinking twice before I deviate from stock.

I put in a Toytec Ultimate Tacoma Lift and OME rear springs. When I installed it I failed to pre-measure the difference and accidentally dialed-in too much lift, ripping both of my CV boots on the first two wheeling trips I made after the install. I swapped the wheels for the previous generation 15" wheels so I could maximize sidewall with BFG 32" tires for enhanced ride when driving fast over washboard. I put on a ARE shell with windoors all around and we absolutely love it for long expeditions. I'm about to install a dual battery/isolator system with solar for those long sojourns south of the border.

All in all, I'm pretty happy with the truck. We've already done some pretty hairy expeditions in Baja and the Mojave without any issues. The rear diff lock has been a godsend the few times I've had to use it! I do appreciate the power and hwy comfort and smoothness over the 3.0 3VZE I had in my 4Runner while not sacrificing fuel economy, even though I'm carrying even more gear now.

I just wish we had as good quality gas here in CA as they do in Mexico. Both my Tacoma and my 4Runner ran better and got better mileage on Pemex Premium than I do here. Damn ethanol . . . at least the Mexicans know that corn is for making tortillas!