My 89 p/u 22re will idle just fine when you're sitting still, but when you apply the brakes the engine idles fluctuate. I tried adjusting the vacuum screw next to the upper plenum but it didnt change any thing. When the engine gets warm, it gets worse. Im guessing this a vacuum leak but im new to yota's so it could be anything. Any ideas?

 

what is your brake fluid level?

if it is low and there are no visible leaks than it could be collecting in the brake booster and getting into the vacuum line when the brake is applied.

could be a faulty air control valve.

or just as simple as a vacuum hose leak

 

Turn your idle speed down:
- http://www.4crawler.com/4x4/TLCA_Tru...ech.04.09.html

The adjustment screw on the intake only affects the fast idle speed when the A/C is on (assuming you have A/C installed).

 

A bad brake booster could be your problem. How are your brakes? Does the pedal seem hard to press in?

 

i've noticed this problem when i've restarted a warm/hot engine that had been shut off only a short time. like running in for smokes. on restart, idle is higher than usual; step on brake pedal and it starts surging. let off, it stops.

does this sound more familiar?

my brakes aren't hard but seem like they require a lot of pressure to stop, but i'm comparing it to my go-kart honda civic so i chalked it up to 'old truck = press harder'

is this a bad booster? what's the current best upgrade/replacement?

 

I agree. Your base idle is set too high.

 

yeah, thats about what mines doing. is there any other way to tell if the booster is bad. If the idle speed is to high, would i just back out the screw on the throttle body, or is there some other way to do it.

 

If your pedal "sinks" to the floor under pressure then your loosing vaccum out the brake booster. This will cause rough idle when the brake is applied.

 

ill have to try that when i get it put back together from my clutch job.
Thanks

 

99% sure this is a high idle problem not a vacuum leak at the booster.

 

thats a possibility, ill check both
Thanks

 

I'm pretty sure that the only way your pedal will sink to the floor is if you have some sort of fluid loss or a lot of air in your brake lines. Your pedal is connected to a rod in the brake booster which with vacuum assist pushes another piston into the master cylinder. So if your booster is bad, the pedal doesn't move any further than if the booster is good. You just won't have vacuum assisted braking.

The only way to tell for 100% certain if it's the brake booster is to press a few times on the brake pedal with the motor off. Wait until there is a bit of pressure built up in the brake system and hold your foot on the brakes. With your foot keeping pressure on the brake pedal, turn your truck on. If the pedal goes down about half to 3/4 of the way to the floor then your booster is good. If your pedal stays where it's at or moves very little then your booster is bad.

You should have other symptoms of a bad booster as well. You may hear a hissing sound under your dash (vacuum leak in the booster). Your brake pedal will seem very hard to apply during normal conditions. Under idle conditions if you mash on the brakes the engine will idle rough and would want to die (like you're describing).

 

i tried adjusting the idle and it worked for a while, then 10 minutes later it started doing it again. i checked the screw and it was in the same place i adjusted it to. should i check the brake booster now, or am i supposed to adjust something else?

 

First you got to figure out why it's idling too high or if in fact it is high. First check engine RPM at idle. And go from there. Anything you adjust is pointless till you figure out exactly what engine RPM is.

 

dumb question: is there any other way to check rpms without getting an rpm gauge, my truck doesnt have one?

 

Many timing lights has an RPM display or some digital multi-meters do as well:
- http://www.harborfreight.com/lcd-aut...kit-95670.html

 

^^^ I have that same one, works perfect. It was also gonna be my suggestion.