Engine Idle pulsing randomly - head scratcher

[Moustache]

Have you checked the Dashpot?

I have been reading for the past week about the Dashpot on these cars and it seems to have a pretty big part in where the butterfly sits inside the TB.

Here's where i got my info on the Dashpot
Dash Pot?? - YotaTech Forums

My issue Looks to be that my dashpot is not connected to the throttle linkage at all. There is a small threaded hole in a tab on the bottom of the linkage but there is nothing threading through it to the dashpot.

As well as the boot around the spring has proken

There is also play between the linkage and my throttle cable, It appears the cable just needs to be adjusted.

This loosness in the cable, along with nothing connecting to the dashpot to the throttle link, I would imagine could cause the butterfly to appear closed but really be slightly open causing the idle to dance around.

I could be totally wrong, this IS just a theory. i'll post up here as soon as i fix it.

Just thought i would mention this before you take it to a shop. I have been to 3 shops and then the dealer. The 3 shops could not fix it, and the dealer wanted over $1400 in parts and labor to replace the entire TB.

 

[lancakyl]

Thanks Moustache. I am going to go look at mine right now!

My 'dashpot' is still intact, and looks very good. I couldn't find anything in my manual for it. Let me know of any other resources you find for this piece.
Thanks

 

[924runnerSR5]

Surprisingly I've heard this solution a few times. I will make sure, but I am pretty sure my coolant is full whenever it does it. I take it you're talking about within the radiator itself, and not in the reservior?

yes when mine used to do it ther radiator was low not thw reservior.

 

[lancakyl]

So here's my latest update:

Yesterday I was killing some time before it got dark- this time of year it's 4:30 in Washington. I was metering some sensors that have been on my checklist. My vane airflow meter was spot-on. Then I metered my TPS (Throttle Position Sensor), and it was way off. When I adjusted it I couldn't get it within spec. Can one of you, with the same problem, meter your TPS sensors, and let me know? It's kind of tricky to get the feeler gauges in there flat without changing the gap, but it's doable.

Before I run out and buy a new TPS I'm going to hit the junkyard and pick up an old one- just for giggles to save a few $$$.

 

[lancakyl]

@ Moustache-

I checked my Dashpot, and it looks fine. One thing I didn't like was that it seems like there is some play in the 'Throttle Positioner' which is opposite of the throttle body, and controls the butterfly within the Throttle Body. The thing I didn't like was that it didn't quite pull the butterfly completely closed.... More to come when I'm not preparing for a test and procrastinating homework.

 

[Moustache]

I replaced my TPS a few weeks back so i cant really say much on that one, its worth a shot getting one from a junkyard but ive read a few places that they can be moody little sensors.

It turns out along with the broken dashpot, the coolant line the flows from the front of the TB into the front of the engine was rusted completely shut. There was no fluid flowing through the TB alloung the sensor to tell the ECU the engine has warmed up, causing the idle to go nuts. This would also explain the gurgling i heard underneath the hood when i would accel.

Replaced my TB on Friday with a used one from someone on here and the idling issue went away completely. Even drove the truck 400+ miles the next day to go snowboarding and it ran perfectly the entire way.

Check the coolant inlet and returns on the TB. If one of them is clogged that may be your issue too.

 

[popageorgio]

OHH MY ..... the last post may very well be my problem with the idle surging. from 1.3k to 3k. This summer the hose from the throttle body to the engine burst leaking coolant causing it to over heat. i ducked tape the thing and got it back home to replace the little hose. I thought problem solved. If i do have a clog some where up there this may very well be the reason. My girl friend does not take very good care of her forerunner but i will be testing this theory soon about the coolant line here soon. Just wondering if anyone knows for sure if there is a temp sensor some where in the throttle body or any where near the intake coolant line. and information would be helpful.'

Thanks again for all the information guys.

 

[lancakyl]

@ Pop
If that doesn't fix it for you, check you TPS. Mine is so out of whack. I turned it all the way down, and it's still metering to twice what it ought to be. It's a lot simpler and cheaper to replace, plus it will take you about 20 minutes to check.

 

[Moustache]

My hose was bulged and about to burst when i caught it. So that there might just be the issue. I'm almost possitive there is a sensor inside there that tells the computer to back the idle down when the engine has warmed up. If the sensor isnt getting enough warm coolant flowing past it, It will not trigger the computer to bring the idle down. As soon as the engine warms up, The surging begins since the computer is still in the "cold loop".

This is just a theory but i really think that was my issue.

Here's a picture of the clogged line i mentioned.

 

[popageorgio]

Good News Gentleman.

I decided to check the coolant hose to the throttle body and when i pulled it off it was chock full of rust and dirt. Well i removed the throttle body from the intake and grabbed the air compressor stuck the blowing tip in outlet when the coolant leaves the throttle body and shot a 1oz rust ball over my camping sleeping bags in the garage. well i cleaned the coolant avenue and reinstalled and now the 4runner is running great. no pulsing and correct idle speed even after a 30 mile drive. Thanks so much you guys for your help i would not have figured it out with out mustashes throttle body replacement pics up top.

 

[Moustache]

Great news man :banana: glad i could help

 

[lancakyl]

Wow I can't wait to see if that's the problem with mine! I bet it is. That hole is a lot smaller than I thought it would be. Congrats!