NRBTFOX

I Know there are a lot of these issues out there, and i have looked at a lot of forums. I just keep getting the same answers. My truck has done this or a while but it just got a lot worse. I forgot my meter at work so these are the things I've done so far and the symptoms I'm dealing with.

Cold Idle- 2000RPM
Warm Idle- 1600RPM
Bounces from about 800-1200 when the brakes are depressed and sometimes just at idle, pretty rough
Smells rich to me

So far I have done the following.

I checked the hose from the thermostat housing to the IAC. Hose and fitting are clear and there is fluid passing through it.
I pulled the idle screw and cleaned the opening and the port. I wiped out the inside of the throttle body while doing this, and turned the screw all the way in.
I went through and checked for vacuum leaks and made sure the coolant was not low.
I unscrewed the idle screw and it bounces faster

I know i need to check the sensors but does anybody have any other suggestions for this weekend without a meter?

Gamma_Hugo

Brake Booster?
TPS?

NRBTFOX

I've heard that it could be the brake booster but I'm not sure how to check that. And I'll check the TPS on Monday.

Hugh_Mann

I had this same issue after cleaning my throttle body. After checking for vacuum leaks and faulty sensors and coming up empty, I narrowed it down to a high idle. I gave the idle air screw a couple turns in and that was it!

Our trucks have a nifty feature--the ECU cuts fuel when the brake pedal is depressed and the rpm is above ~1100 rpm. What's the sense in dumping fuel into the engine when you're trying to stop, right? This is why your idle bounces up and down when you press the brake. The ECU senses that the rpm is above the ~1100 rpm threshold and cuts fuel. The drop in fuel lowers the idle, the ECU senses this and reapplies fuel. Your engine then shoots back up to its >1100 rpm idle and the process repeats.

In my case, the gunk around my throttle plate was actually sealing it, and by cleaning it created a sort of "vacuum leak". I know this because after cleaning it, light shone through the gap between the plate and the throttle body itself, where none did before. The extra air passing through the gap increased my idle to >1100 rpm which caused all the issues you're describing.

NRBTFOX

Maybe I should have reworded my above post As of right now my idle screw is twisted all the way in and it doesn't seem to have much effect on it. If I start twisting it out it just makes the bouncing much more rapid.

toyota4x4907

Adjust the ignition timing and idle speed to spec following Toyota procedures.

NRBTFOX

Me and a friend that's a really big Toyota guy did it about six months ago when I was complaining of lack of power going up hills. It should be spot on.

I'm not a mechanic... I build boats...

Hugh_Mann

Hmm, well I guess you'll have to check for vacuum leaks and faulty sensors. I did that before I ever messed with the screw. It's good to eliminate those possible sources anyways.

Check your throttle position sensor and follow 4Crawler's instructions:
http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml

Also check your auxiliary air valve/idle air control valve. Beyond that, be on the hunt for vacuum leaks. Have you taken any vacuum lines apart recently? Do the bellows on the elbows of the main intake tube have any cracks?

NRBTFOX

I actually tore out most of vacuum lines and got rid of the egr about six months ago hoping to alleviate this problem. I looked today for leaks to no avail but I will look again. I know I need to test the sensors still but my meters at work. Is there a way to test the IAC?

I'm not a mechanic... I build boats...

jennygirl

It's okay I'm not a mechanic either

I did however completely disassemble my IAC the other day, and it made a huge difference in the idle. I think the biggest difference was the adjustment, though- not the completely disassembling it part.

Basically you want to make sure it is open the right amount at room temperature. You'll have to remove it out of the car to make that adjustment though, because you have to be able to see through the air passage. There are two air hoses (on the front and back of it) and two coolant hoses that pass over the bimetal that actuates the valve. Remove both air lines and coolant lines, and pop it out of the car.

Then loosen the adjustment screw and move it up or down to adjust it so it looks kinda like this:



(I had to open mine up a bit or "increase")

NRBTFOX

I'll pull it out and check it today. I was gonna pull it out yesterday and decided to wait. Should've just done it. Thanks for the info.

Hugh_Mann

Just FYI, that diagram is for the early style AAV. My 1993 22RE is has the later style and checking it is a whole other ordeal. I saw a thread where a user basically plumbed it into a jimmy-rigged hot water system on his workbench to see what temperature it opened. Wish I could find the link for that. Anyhow, it isn't a simple matter of looking through it to see if it's opened at room temperature. I'd caution against adjusting it if you indeed have the later style AAV. If you have your cold idle improperly set, it'll mess up your warm idle.

Edit: If yours looks like this then you have the later style. Used compressed air and TB cleaner to make sure the coolant and air passages are clear.

NRBTFOX

Yea. Just pulled the throttle body off and realized that. I'm gonna clean it up a bit more and put it back together. I'll check again for leaks then go to checking sensors.

jennygirl

Good to know Hugh_Mann. I had a feeling it may be different- I have read about people swapping older throttle bodies for the newer ones. But now hearing how hard it is to adjust the newer ones I think I'll have no issues sticking with the older style

NRBTFOX

I just checked the TPS. It looked to me that it was in spec. It's dark now and I had my hands full plus a flashlight in my mouth. I'll check it again tomorrow to confirm.

NRBTFOX

Upon rechecking today it seems that my TPS is in spec. I also did the checks I could do with a meter on the mass air flow. Again seems to be good.

anndel

Maybe vacuum hose to master cylinder is leaking either the hose it self or the clamps at either end?

turkeykiller365

My chevy does the same thing from time to time (5.3 V8) itll idle there right at like 800 rpm, but then itll start to bounce between like 300 and 800. Then when the brakes are depressed, especially if turning at the same time, at idle, the engine would die. The first time I fixed this with a new oxygen sensor and plugs/wires etc. Second time it started acting up again, it was a dirty throttle body (but you said you already cleaned that). idk. just some experience input

NRBTFOX

I'll be out of town for the next few days. Once I get back I'll start working on it again. The next thing I was gonna do is check the actual throttle stop screw and make sure It's allowing it to get to idle, and check the o2 sensor. I'll let everyone know if I get anywhere.

andykrow

Throttle stop screw is a good thing to check, and make sure you are actually checking that and not the dashpot set screw. Mine was messed with and my throttle fluctuated by 200-300 rpms.

How I set mine: First clean the hell out of the butterfly and area around it in the throttle body so no egr buildup is messing with anything or causing the throttle to stick. Then back off the set screw until you can feel the butterfly stick in the throttle body when you open up the throttle. Then tighten the screw until you just feel the stickiness go away. Check after you tighten the locknut because that will ness with things a bit too. Basically you want that butterfly as closed as it can be without sticking. I don't know if this is the FSM way of doing things but it worked for me and my idle is steady now.