truck idles at 1600 and surges when the brakes are applied. i think its a vacuum leak but where. i looked and tried the lines and nothing. how else can u tell

 

did you try turning your idle screw down? if its set too high that will happen but to find a vacume leak you spray ether (starting fluid) around all your vacume lines and if your idle surges more you found a leak. some people recomend using an unlit propane torch instead of ether but it doesnt really matter which one you use.
what engine do you have?

 

My truck did that for a while. I found it to be a semi-stuck valve-thing that cushions the throttle when it closes (located right to the side of the throttle body). Mine was kind of stuck, so I took it off (and never replaced it!). My truck runs better without it, in my opinion.

 

i have the 3.0 v6. i can screw in the screw which makes it run rich and it kinda stops. it i lean it out it surges faster. when the brakes are applied it drops rpms and still surges. im clueless!

 

The brake -surging problem is pretty common, when you depress your brake pedal it tells the computer which cuts fuel to the engine to be more economical.

 

so its normal??

 

Seems to be, mine does it VERY slightly though.
But since my truck has a lumpy idle, I dont notice it anymore

 

(dash pot)




The surge is caused by the ecm cutting power to the injectors to slow it down, then when power is restored the idle goes back up. Up, down, up, down...

The theory is that if you're stopping and the idle is too high, and if you have an automatic transmission , that the high idle can push the truck a little and make it harder to stop.

In practice this is a very idiotic solution and a major oversight on the engineers part... I have a few bad sensors that make my idle kind of erratic, and when I set the idle to the best compromise every other day the surging was unbearable.

I fixed mine permanently by cutting the brake lead to the ecm. It's a very bullish way to fix it and meets with mixed reviews, but I had no drawbacks at all and the surge is completely eliminated. Just search for surging idle and look for the thread I started. I have a 22re but it should be similar to the 3vze you'll just have to test the leads before you snip.

Your idle will still be high but the surge will be gone.

 

overdrive -- thats a note that I am storing in my head for later use -- thanks