Throttle Sticking on 2.7 liter

'98 Tacoma 2.7 auto 176k miles

I am in the process of getting to know, and fixing any abnormalities in my new-to-me Tacoma, and one issue is a sticking throttle as noted when adding throttle from a throttle-off condition.

About 20% of the time, when starting from a stop (or almost stopped) I put my foot on the throttle to accelerate, the throttle pedal won't move without having to add extra pressure, at which point the pedal breaks completely loose (as it should have initially), and the truck lurches ahead uncomfortably. The truck responds property the throttle-the :lurch" is because when the "catch" lets go, the pressure on the pedal necessary to break it loose causes it to more farther than intended, causing the lurch.

The other 80% of the time, the throttle moves off-idle position normally and smoothly, and it NEVER sticks or hangs up anywhere else in its mechanical range.

I can move the throttle plate under the hood, using the throttle quadrant the cables pull against, and there is absolutely ZERO friction. I can do the same by removing the cover from the box on the right fender liner where the cables motion is transferred, and that pulley and the cables are 100% free.

In fact NOTHING I can do when the truck is sitting not running, or idling in Neutral that duplicates the sticking I feel a good amount of the time I am driving it and attempting to accelerate from a stop. I have of course knelt along side of the driver's door and operated the throttle by hand and again, no sticking (or "catching" if you like).

I am wondering if this is something someone else has experienced and figured out?

Bob
*I have felt this kind of sticky behavior when the throttle plate closes at idle more than it should, jamming ever so slightly in the throttle plate bore until it opens a couple of degrees. But as far as I can tell, this is NOT the issue here, and when operated at the quadrant/bellcrank, it closes easily against the throttle stop, and rotates off idle without the slightest friction or "hanging."

 

I have a 97 4X4 2.7 AUTO I purchased new and experienced exactly what you have described here. Everything seemed to operate smoothly and did a complete fault trace, (cable, etc.) with no resolve. I finally removed the Throttle body and cleaned it completely including the Idle valve on the bottom. It was heavily gunked up in the butterfly flap. Problem solved. Collect up all of the gaskets and cooling hoses, remove the throttle body and do a complete cleaning. I also use Shell or Chevron premium fuel and have had no issues for the last 150,000 miles, I am at 280,000 now.

 

Check where the throttle cable comes through the floor . My floor cracked and it would put pressure on the cable causing it to bind

The linkage in the cab can get dirty and stiff

 

I have a 99 prerunner 2.7 std cab auto, had that very same issue at about the same mileage (few years ago) drove me nuts, cleaned throttle body and even used a motorcycle cable lube fitting to lube the throttle cable and the transmission feed back cable, no joy. This makes NO sense buuut I replaced the throttle position sensor and poof no more off idle false detent, please make this your last effort to resolve the issue, try what others above have mentioned first. I now have 230,000 miles and no more issues, I use non methanol fuel

 

I had the same problem, tried the above solutions to no avail (160k at the time) the butterfly was hanging up due to a tiny bit of wear in the throttle body bore. It was obvious when holding it in your hand. I turned the throttle stop screw an tiny bit, less than an eighth of a turn. Problem never happened again. The idle will be high momentarily but once the pooter figures it out, it will drop to where it needs to be

 

I was thinking the same thing! Even though the throttle doesn't hang up when I move the butterfly under the hood, this morning before I checked the excellent suggestions above, I took a chance and did EXACTLY what you did and loosened the jam nut on the throttle-stop (had yellow paint on it) about 1 flat and advanced the center screw ( small Allen screw) about 1/4th turn and re-tightened the jam nut.

I installed new drilled front brake rotors and ceramic pads, and pulled the rear drums and found new shoes already installed so just de-glazed the shoes and lightly sanded the shoes and put them back together. I took the truck for a short ride, and come to think of it, the throttle did NOT stick once (but I didn't drive THAT far, so maybe my ride didn't prove anything). So HOPEFULLY...

I DID clean my throttle body and butterfly previously when I had the intake tubing off to pull the plugs to replace them and do a compression check (I was amazed to find all cylinders at 200-202 psi when I was expecting about 180psi at the stated compression ratio), but it didn't clear the problem unfortunately.

I'll return if the tiny throttle stop adjustment helped. Could easily be the other things as well. Good to know this is a somewhat common problem!

BTW, I was wondering if the TPS is supposed to "click" just off-idle like older BMW's TPS do because mine does not.

Thanks,
Bob

 

No, but you can hook an ohmmeter up to a certain 2 terminals on the TPS and check that it goes from continuity to no continuity when the throttle moves away from closed. In fact, this is how you set the TPS to the proper position. The procedure is given in the repair manual.

The throttle stop screw is supposed to be set to prevent the throttle plate from jamming into the bore when it closes. The throttle plate still closes completely, but the screw absorbs the force rather than the bore. I'm not sure why yours would be out of adjustment. Maybe the end of the screw or contact got slightly worn over time. My only concern would be if you turned it too much the TPS won't register the throttle at the idle position, but it sounds like you barely moved it.

 

Yes, I moved it just enough that I hoped it would keep the butterfly from jamming. I moved it so little that I didn't observe any increased idle when I started it the first time.

I will pull the TPS plug and check for the TPS continuity as the throttle closes completely still. I'll see if I can find a genuine workshop manual if I can find one at a reasonable price. I prefer paper, but will settle for what I can get. My last choice is a Haynes type, but if that's all I can get, I will get one of those despite the fact ones printed in the past 20 years or so are pretty elementary.

Unfortunately I was too tied up over the week-end to drive the truck, but over the next couple of days I will do so and report whether the sticking has stopped or continues.

I did Saturday replace the front rotors (with drilled rotors) and the pads (with ceramic friction material) to see if they would improve braking. The truck as I bought it took way too much brake pedal pressure to stop it. I also removed the rear drums to check the lining on the shoes. They were like new (probably recently replaced) but I lightly sanded the linings and drum surfaces to remove any surface glazing from use. The result was a pleasant reduction in the pedal force necessary to slow and stop the vehicle. The old rotors weren't warped or badly worn, but the cost of the complete set was so reasonable I couldn't resist renewing them.

Bob

 

There are some PDFs of the Toyota repair manuals somewhere. Maybe someone can post the pages showing the TPS procedure for the 98 2.7 engine.

 

They aren’t that sensitive. If you read live data it will read 11-14% with throttle closed. The computer will figure it out as its driven.

 

There is a separate circuit that is on/off to detect idle/non-idle in addition to the variable resistance circuit that detects throttle cable angle. Toyota changed the TPS over the years, but usually it's not just detecting the angle.

 

TW members have done this with success.

http://maxbore.com/

 

That's what I figured.

1) A "switch" to determine if the throttle is at idle, or not, and
2) A sensor telling the ECM where it is for anywhere else in its travel.

The truck idles perfectly after my minute "adjustment," so it's probably still OK.

BTW I have driven the truck enough no to know that my small throttle-stop adjustment (maybe 1/2MM measured at the stop) fixed the problem beautifully.

Perfectly smooth pedal movement from idle on.

 

Do what you feel necessary but it worked flawlessly for me. Good luck

 

Drove the truck extensively today and no sticking and the idle is perfect. I am sure I didn't move the idle stop enough to affect the TPS calibration. SO nice not to have occasional sticking where you'r e never sure if THIS is the time it will take more pressure to move it, so when it lets go, you "jerk off the line" when the throttle breaks free and responds (too much). My wife is even thrilled at the "no jerk" acceleration from a traffic light.

 

It was a real joy in traffic, nothing like having a foot on the brake and one on the gas.... glad it worked out.

 

Glad You got it resolved !