I have an 88 pick up w/3.0 that idles about 2grand when cold. After it warms up to normal operating temp the RPM's drop down and surge between 1000 and 1400. There are no codes showing, I have replaced all the vacuum lines cleaned the throtle body checked the air cleaner, Cleaned the VAF, TPS, and replaced the fuel filter. Also if I turn on the A.C. the idle will jump back to about 1800 and smooth out a little. Any help would be greatly appreciated

 

Check your timing and the idle speed screw on the throttle body.

Too far advanced timing will cause the ECU to keep cutting fuel as it gets too high, letting rpm drop below idle, and then surge back up...

Idle screw has a small rubber washer on the end of it. Sometimes it gets old and brittle and lets excess air in, messing with the idle. Can be a pain in the ass... as I found mine would get jiggled by the truck starting and shutting off, but not by running. So tricky to pinpoint it. I would just screw it all the way in, counting turns as you do, then take it all the way out to look at the rubber.

What does the truck do when you jumper the diagnostic port? If the idle smooths out, I'd be leaning towards a TPS issue.

Note: 2k cold idle is about normal, if it's pretty chilly outside.

 

I agree sounds like TPS, you said you cleaned it. Did you check it's adjustment?

 

Thanks for the help
I'm on duty at the firehouse for the next 96hrs so I can't get very deep into the truck. I did pull the idle airsscrew and cleaned it up.(unbelievably nasty) put it back in ...everything runs great now. Haven't got out on the highway yet but it looked good.

Thanks for the help

 

I would take the idle air screw back out and replace o-ring on it, that thing got to be harder than a rock. How did you clean the TPS?

 

It can be a little annoying how the tiny things have such a large effect. Hopefully that's all it was!

 

got a chance to put a couple of miles on the truck today. Sorry to say the oring on the idle screw is still leaking so now im on the hunt for an oring or maybe a whole thotle body rebuild kit. Ill let you know the outcome

 

Well no luck finding a new O-Ring for the Idle air screw so I thought I would try an old trick and soak the O-ring in brake fluid over night and shazam everything is back to normal. Thanks for all the help Im sure Ill need lots more.

By the way does anyone no where I can get a new idle air screw

 

Well after testing and calibrating the TPS replacing the o-ring on the idle air screw, testing the VAF, check the timing, and replaced all vacuum hoses the idle still surges. It is not as bad as it was before but none the less its still there. Somedays the truck runs like its brand new others the surge will start when I apply the brakes at a stop light, when I release the brake the idle will jump up to around 1600 and hold steady. I am totally out of ideas.

 

It sounds like you still have an air leak.

The ECU will cut fuel if it sees the engine above 1800RPM, AND the TPS is saying that the throttle is in the "idle" or closed position. Your surging is caused by the engine speed increasing up to 1800rpm, the ECU cuts it out, which drops it back down, then the ECU stops cutting, and the engine goes up again. The fact that SOMETIMES it doesn't surge, but instead holds at 1600 means that the air leak is inconsistent. Sometimes it doesn't leak anything and your idle is normal, sometimes it leaks a little to get you up to 1600, and sometimes it leaks a lot to get you above 1800. The fact that it is running otherwise fine means that it's almost certainly METERED air. This means that the air is coming from somewhere between the AFM and throttle, and is being fed into the intake after the throttle. Things I would check:

- I'm not a V6 guy, but the 22R-E has an idle air valve which opens up when cold, I assume the 3VZ-E does too. Make sure that is operating properly, maybe even try blocking it off.

- PCV system. If your PCV valve has a weak spring, it could be sucking in WAY too much air, basically allowing a straight path between your intake pipe through the valve cover into your intake manifold.

 

I tried to find that little o-ring through Toyota, they didn't have a # for it. I searched on here and found a link with an o-ring that Grainger sells, it's close but not the same.

 

well ive spent the day going through your suggestions still have the same problem. When I put the ECM into test mode i now get a code 41 which is the TPS (if I read the book right). So I guess I need to pull it back off and check it again. Anyone know how precise this needs to be? I dont have a metric feeler gauge set.

 

Throttle body cooling passages blocked?

Throttle body vacuum passages blocked?

 

When I adjusted the on on my 1JZ, it was a SUPER precise measurement. Like a hair off and it was a mess. Took me several tries to get it right.

 

I've found that you can adjust them by ear pretty darned close.

First, replace those ˟˟˟˟˟ty philips heads with allen head bolts. It's also easier if you remove the hood (3 minutes, 4 bolts). With the engine HOT & running, just slight loosen the bolts enough to be able to turn the TPS. SLOWLY turn it down just until you hear the idle drop. Tighten it down & drive it! Pretty close to what it should be & you'll save a ton of time.

 

That's actually not a bad idea! I'll have to remember that next time I ever adjust one.