Sticking Throttle

Does anyone know what would cause a sticking throttle other than a dirty throttle body or stuck throttle cables? The throttle has started to stick when accelerating from an idle. Sometimes I have to blip the throttle to break it free. I thought this would be a dirty throttle body, but the throttle is very smooth when the engine is off. Any idea what would cause this? I am thinking maybe a vacuum issue that is related to the engine running.

 

Try to replicate the sticking with the engine off from inside the truck and at the throttle body. If it sticks then it's not vacume related.

If you can't replicate it with the engine off then try with it on in park not while driving. If it happens while the engine is on and you think it's vacuum related go to auto parts store and buy several feet of vacuum lines and start replacing them all. It's a 96 20 year old rubber.

 

Duke,

I think we're on the same page. I've had another truck where the throttle body was dirty and causing a sticking throttle. But you could feel the stickiness with the engine on or off. In my case it's only when the engine is running, but only when accelerating from an idle. I'm not real familiar with the vacuum system and how it affects the throttle body operation. I just wanted to see if anyone thought that could explain the issue. I'll replace some hoses and report back.

 

Also you can remove the throttle cable and manually move it and see if it buinds up. Try to isolate the components so you can eliminate working ones from the culprit.

 

I had/have the same issue on my truck. I noticed it happens more when it is cold outside or I haven't driven the truck in a while. Although it has not happened since I cleaned the TB. I would move the butterfly valve by hand and see if there is any resistance.

 

Do you have cruise-control ? If so does your throttle cable go thru the CC actuator?

 

Think about adding a few extra ground straps .
As mentioned above , its a 20 year old truck . There is a chance the throttle cable is becoming a ground for the cab to the frame . Have seen this hundreds of times

 

Might want to look into the throttle position sensor on the t-body. Check for "smooth" progression of ohm readings through the range of throttle motion or the progression of throttle plate position values on a diagnostic reader.

The frame on a 1st gen carries no electrical loads, there is no frame ground wire/cable. The frame is grounded only by default through brake/fuel hard lines.

 

I think I figured it out. Since I have a manual transmission there is a dashpot on the bottom side of the throttle cable at the throttle body. This helps to slowly lower the throttle when you take your foot off the accelerator. It looks like the dashpot is actuated by a vacuum line. When the truck is off there is no vacuum and the dashpot actually sticks out just far enough to contact the throttle linkage and keep the butterfly valve in the throttle body from completely closing. With the engine off, I could depress the dashpot all the way back so that it is no longer in contact. Then I can feel the sticking throttle body by hand. Long story short, it looks like I will be taking the throttle body off for cleaning after all. Are there any hidden gaskets I should expect to replace, other than the one on the right side of the throttle body?

 

You could probably just reach in far enough to clean the throttle plate area with it installed.

If you take it off you might consider taking the IAC valve off to clean while you're at it. You'd need a new gasket for that and the screws can strip easily. Check the small coolant hoses too. If they're original you might want to replace.

 

Yep, like DrZ said, a quick wipe should tell if that's your problem, a more thorough cleaning may or may not be needed.

FWIW that part with the vacuum line is called a "throttle opener" and seems to be working correctly. It's sole purpose in life is to hold the throttle open a tad to allow increased airflow for starting and starting only. Once engine starts and vacuum is present the plunger retracts allowing the throttle to close.

 

Here is a write up with pictures for a 2.7 litre throttle body cleaning
How to for 2.7 http://www.tacomaworld.com/forum/1s...o-throttle-body-intake-manifold-cleaning.html

 

All the more reason to add ground straps . Toyota,s were the worst for the melting throttle cable condition . I have seen these cables melt to the point where they catch on fire . It was also a common problem with the transmission linkage on the automatics .
Its not the problem of grounding the frame . It,s the issue of ground conductivity returning to the battery

 

The 1st gen Taco has no electrical loads that use the frame as a ground path, period.

 

Having a similar issue with my 96 Tacoma 2.7, I found a very simple solution. There’s a throttle plate stop screw that I adjusted very slightly and it now works perfect. I know these things are factory set and sealed, but I’m sure there was just enough wear for it to require adjustment. I only had to turn it in about an 1/8th of a turn also.

 

I am considering doing the same thing. My truck does EXACTLY the same thing. I suspect the bore to be worn and the butterfly just hanging up under the motors vacuum. I can feel it catching when turning it at the throttle when warm and under idle. There’s a little play in throttle shaft bushings too but I’m fairly sure adjusting that stop just a fuzz will end this headache. God it’s annoying, especially in traffic ....