Rough Idle
 

Hey guys, I recently performed a head gasket replacement on a buddy's 4runner, 01 Limited. It's not my first time doing a head gasket. We got everything buttoned up yesterday afternoon and fired up the truck only to find it running very rough and dying. It would not run.
We tripled checked the timing before closing everything, rotated the crank twice by hand everything lined up great. Is it possible to jump timing when first starting it up?

So far we swapped the plug wires, truck runs but is very rough still. Giving it some gas smooths it out but it won't find a clean idle.

Vacuum leak or intake leak are what we are thinking. (Low rpm to much air engine rough, higher rpm the extra air is OK engine smooth)

We did have two vacuum line connections that did not have a line to hook up to after removal. First is the vacuum line to the left of throttle body, researching where this needs to hook up to.
Second vacuum line is at the back of engine exactly where the fuel supply line runs, it's a vacuum line connected between the two cylinder banks with a y connector but no line. (Attached photo)

Attached photo

Did it throw any clues via CELs?

For the 3.4l there is a vacuum air assist that ports air from the IAC to a Y that splits and goes to each side of the intake manifold in line with wheee the injectors mount in it.

Yours being an 01 I do not know if your engine has this same setup.

Also that IAC has a coolant line going to it and it’s easy to get the air assist and coolant lines swapped. But once again I do not know if your 01 has the same setup.


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The Vacuum nipples behind the valve covers run in line with the fuel rails and tie in together into a y connector. There is a slightly bigger line from the air control to the y connector it's the air assist hose. The other 2 hoses on the iac are the coolant bypass hoses.

So I verified the timing was spot on, cranked the truck still same idle. I'm tearing it down to intake manifold make sure gasket there is good..after that going to try the IAC. It looks like we are only missing the hose from the y connector to the left side of the throttle body, If I understand that correctly. The right side connector and bottom are the coolant bypass,

The yellow on circled is the one I belive goes to the y connector can someone verify?

yep that's the air assis hose.
this might help.
2001-2002 Throttle Body Design Question

I ran out and traced mine quickly.

Here's what I've got (hope this helps).


First photo is a poor attempt at tracing the line back. Imagine it going under the TPS sensor/connector.

Second photo is where it ends up, which it looks like may be your first photo in the thread.

What are the chances! I'm having the exact same issue, took my 01 runner to get the head gasket replace due to a small leak along with the timing belt, any time I start her up she's idling way higher than normal. I just ordered a new throttle body in hopes it was the culprit to my problem as I'm also getting two CEL codes, P1128 and P0128.

Hey guys, thanks so much for the help. This community is really top notch.

Update this morning:
Had the intake down to the manifold gasket, found atleast half a gallon of coolant in the Valley. This lead me to believe the manifold gaskets were installed wrong or the intake manifold itself wasn't tight for some reason and didn't seal.

Got the gaskets right, tighten everything down good and flat.

Truck still won't idle correct, it's not an high idle issue it's a low idle. I see today it has a CEL I have to get my scanner from my brother and find out what it a throwing.

Fuek/Spark/Air??? Can the air assist hose missing throw the idle off this much??

A new throttle body should do it, if you picked up one with the TPS on it.

I just replaced my TPS after a high idle issue. First was a high idle, then after cleaning the TB and likely fouling the TPS the idle would surge between 1-3k.

I ordered a new TPS and was able to get it purring back around 700.

So, if you're up for it you may be able to fiddle with the TPS and or get a new TPS to see if that is what is causing this. Otherwise a more expensive route would be to replace the TB with an OEM unit which should come with a new TPS on it.

I was doing some research around the forums however I thought the TPS sensor was not sold by Toyota for the 01 and 02 models as the connection is a 4pin instead of the 3 pin on the 96-00 models? This link elaborates further.

Write up: 01-02 T4R Throttle Position Sensor Info

Correct. Check out post #18 on the link you sent.

Parts geek sells the 4pin as that is the one I bought and installed (successfully).

Here’s the one you want on their parts list: Throttle Position Sensor - Aisan W0133-2744128

2001 4runner throttle position | Partsgeek.com

Update:
 

Hey guys final update, I finally got everything going good.

Here's what solved my issue,

1. Cleaned the IAC ports and the throttle body through and through.
2. Attached that air assist vacuum line.
3. Make sure my exhuast was completely tight no leaks etc.

Not sure what solved my idle issue maybe 1 and 2 but she purs now. ( Besides my ac idler pulley deciding not to spin at first, fixed now)

Thanks again for all the help and support.