Hello to all and appreciate any insight and help anyone can give.

So I just finished my rebuild of a 91 3vze 4x4 and Im stumped as to why i have such a high and undriveable idle (1900-2000). I have a couple different symptoms when I start it up, both of which have been gathered from starting the rig up about 20 times and i get either symptom at random.

Case1: Upon start it shoots to 2300rpm and drops to 2000 and I can play with the timing within the slot confines and it will go up or down for about 10 seconds. After those 10 seconds there's hardly any change twisting the dizzy and it will idle at 1900rpm for seemingly as long as I let it.

Case 2: I fire it up and it gets to 2300rpm and idles gradually drops to like 500rpm. It takes about 40 seconds and it will idle til it peters out no matter what I do with the dizzy variable.

Now I've pinched all my vacuum lines to see if i can get any change but nothing. Nothing that I know to do seems to change other than the occasional dizzy twist.

If i get my timing light at the stock 10 degrees btdc the idle is still high as before.

Any clues as to what I'm missing?

Thanks again

 

Is the throttle closing?

Lots of 4runners and trucks have a lot of "stuff" hanging on the throttle plate. In addition to the gas pedal, you've got cruise control, automatic transmission linkage, throttle opener, and dashpot. If any of those get sticky, the throttle won't close, and it's just like you're resting your foot on the gas pedal.

Next time you start it up, wait about 2 minutes, then push the throttle closed. Does the idle drop and stay there? Clean up the linkages (don't use oil or grease).

Note that the higher idle at start-up doesn't have anything to do with the throttle plate. Idle is lifted by the ECM setting ignition timing. When the ECM gets the word from the ECT sensor that things have warmed up, it will reset timing closer to base to drop the idle.

 

Engine warm, throttle plate closed, tps IDL signal sent, set the base timing and quit moving the distributor. Fiddling with the base timing is not helpful.

There are three common and simple causes of erratic idle. A bad oring on the idle screw (it's like a dollar just replace it), a worn throttle plate shaft (LCE sells a fix it kit for this that includes a bushing if you can wiggle the shaft at all and percieve idle changes or movement, it needs repaired), and sticky idle air by pass. Cleaning the throttle body, which is a typical step in a rebuild just makes these more likely to show up.

And PS pinching a vacuum line with a leak down stream of your pinch point doesn't stop the leak. Replace any vacuum lines that aren't tight when you try to rotate the tube on its nib, if your short on funds grab some clamps from HF and it'll help a lot or a little depending on the vacuum line tubes condition.

 

Had a chance to try some of your suggestions this morning

@scope103 I didn't yet have the throttle or auto trans cable installed yet so if i do have somethings that sticking or getting held up, I wouldn't know just yet. I also have a new ECT sensor since i banged all my sensors on the firewall when i pull the motor and trans

@Co_94_PU I went ahead and changed out the idle screw o-ring since it's easily accessible and probably hasn't been changed in 29 years.

After changing that and installing my TVV correctly (previous owner that I took pictures of didn't have it done right according to the FSM) the truck will idle fine upon start for about 5 seconds and surges to 2300 rpm again and stays there

The shaft that goes through the butterfly valve appeared to be solid when i cleaned the throttle body.

I'm not familiar with idle air by-pass that could be sticking. where is this?

I took the TPS off when i cleaned the TB could that lead to this problem?

 

I don't know much about the 3VZE, but on a 22RE the TPS being slightly out of adjustment can definitely create an erratic idle.

 

If you don't know it's definitely not right, and neither is your base timing.


You have a Factory service manual, or atleast a Haynes or Chilton, right?

 

If this isn't done correctly you can't set base idle&timing which means you can chase it all day and its never going to be right because the ECU is going to move it.

 

It was my TPS not being calibrated as well as a hole on the front of the plenum i didn't realized was a hole that went all the way through and not just a mount.

Finally got my rig going after almost 6 months of trial and error from a layman, a book, and internet access.

Thanks to @scope103 and @Co_94_PU for all the help on just about every question I've posted. You both seem like great, no nonsense guys lol.