Has anyone ever figured this one out? When I hit the brakes (only when I hit the brakes my idle goes up and down) But doesnt do it when the engine is cold. Only when its at operating temps or warm. My idle screw is set good. My truck has always done this..

Thanks,
Mario

 

My '94 did this for a little while. There is a valve that bumps the idle speed up when it's cold. After the engine heats up the valve should shut itself off and let the idle return to normal. Mine was clogged and not operating properly.

There is a separate system that uses the a vacuumn line and the brake booster to cut fuel to the injectors when you step on the brake, if the engine is above a certain RPM.

In my truck, the two systems were operating against each other, and if I was off the brake it would idle reall high, but on the brake it would surge up and down.


Search this forum and you'll find a bunch of other threads about surging idle.

 

whats your idle speed set at?

 

Mine did this and it was a reasult of a worn throttle body. Took like 2 years to figure it out. It wasn't sealing when it was shut.

 

Mario,

My 88 Toyota 4WD Pickup has recently started having the identical symptom your describing. I'm the trucks only owner, have you gotten a response on your problem.
I haven't had time to sort out the source of the problem or what might cause it.

Del

 

if your idle is set above 1000rpms it will do that so turn it down to 800rpms

 

Mine is set at 800 and does it, could it be the break booster?

 

These guys had this question so many times they made a sticky out of it... I haven't had a chance to try their recommendations yet but it sounds dead on.

http://www.toyotanation.com/forum/t113388.html

 

4crawler says to adjust your TPS... it's *kind of* easy to do.