91muddog

Ive seen some similar reports of this problem lately, and its drivingme crazy!
Hopefully someone can be of some help.

The problem is very consistent. If you start the truck up after being shut off, even if its only for a minute or two the problem isnt there..
After driving down the road, the first stop i come to, as soon as i touch the brake peddle the engine will surge. RPMS drop from idle, come back up, drop ect...
There is no difference with the amount of pressure applied to the pedle. It starts as soon as the brake lights come on, and stops when they go off.

The brakes work great, there appears to be no loss in the booster, all of the vaccum hoses and intake gaskets are good, i double checked them all with carb cleaner today.

any ideas?

angrybob

How does the truck cold start with the brake pedal applied while cranking? How does it hot start with the brake pedal applied while cranking?

If you've confirmed all of the vacuum lines, my guess is that your booster is has a leak to atmosphere in the cabin. You draw in atmospheric pressure from the front of the booster (the part that sticks through into the cabin by the pedal box) through the filter just behind where the booster pushrod clevis connects to the brake pedal. If there is a leak there, you will have a direct path for intake vacuum to leak to atmosphere when the brakes are applied. Depending on the size of the leak, it shouldn't cause a hard pedal either (the normal booster failure symptom).

If your truck starts easily with no brakes and difficult with the brakes applies, the above is likely true. If no difference, than probably not.

One easy thing to confirm - pull your booster check valve and make sure its still one-way flow.

xxxtreme22r

What RPM is your idle at? It could simply be the fuel cut that is triggered when idle is to high when the brake pedal is depressed, find out what rpm is ad then why. Eliminate any possibility of vacuum leaks and whatnot that cause high rpm before resetting the idle adjustment screw.

angrybob

^^^^^^Good point.

Another easy test after you confirm vacuum lines and the above idle check is to disconnect & plug the intake vacuum line. The brakes will suck and be in full manual mode, but drive around your subdivision carefully. If your condition is gone, its another check mark that the booster is bad. If the surging is still there, its not the booster at all.

4Crawler

iTrader: (3)

x3, idle is likely too high. Why? (see the 2nd Q&A below):
- http://www.4crawler.com/4x4/TLCA_Tru...ech.04.09.html

91muddog

thanks everyone, you are awesome! and thanks 4crawler for the link.

i dont know what the idle currently is, this truck doesnt have a tach, need to do the sr5 cluster swap soon!

i will try adjusting the idle and let you know how it works!