2003 Avalanche stalls at low speed when firmly applying brake.

Hi! It's a vacuum leak, most likely. Some times the vacuum hoses are cracked and they don't look like it; some times the oil fill cap is allowing air to be sucked in; some times the air intake hose (duct) is cracked and allowing air in. That is the "easiest" thing to check. If the hoses are good, it could be a stuck PCV (positive crankcase valve).

On my Toyota the air intake hose was split underneith where it was not visible, and the vehicle was doing exactly what you described above. I patched it with duct tape, bailing wire, and more duct tape because I'm poor white trailer trash, and it solved the problem.

That's unlikely to be the cause, vacuum leaks tend to increase the idle, not decrease it. This is more likely the cause.......

with that, as a matter of course he should pull any stored codes with an OBDII reader and see what's there.

Uh, it is an obsewrved fact that a vacuum leak can cause low idle and stalling when the vehicle comes to rest.

Please do the following test: start your vehicle's engine (if you have one) and get it up to operating temperature; then unscrew the oil fill cap and remove it. Or disconnect the air intake hose.

An unusually high idle is indicative of a vacuum leak. This is pretty common knowledge....pull offyour PCV hose and see what happens if you don't believe me..

Did you do the test I suggested? If you did you will have discovered the engine idle speed will decrease. This is also true for a bad air intake hose and other vacuum hoses.

Did you do the test I suggested?

Did you do the test I suggested as well?

Not yet.

Dear idiot,

Giving people wrong advice is not doing them a favor.

Then, of course, there's the type of idiot who thinks that an engine with a vacuum leak can only decreases the idle speed.

And, of course, ignore the fact that I gave him what was likely the correct cause, a common issue with the throttle bore buildups. Plus checking for thrown codes with an OBDII scanner. I'd be looking for lean trim codes caused by unmetered air entry. So who's the idiot here?

Gentlemen, Gentlemen, play nice.

I removed the intake and noticed a considerable build up around the butterfly valve. I liberally sprayed Throttle Body Cleaner to remove the schmegma and whaddya' know.......... it worked. The truck idles fine and no longer sounds like it is going to die on me when the defroster kicks in.

Thanks for the advice.

BG.

Glad it worked out for you. Have a good one...