89 S10 Blazer Brake issue
 

I have the 2wd, 4.3L TBI engine, auto trans. What would cause the following: With the engine on, I have a rough idle regardless if it is cold or warmed up, but if I apply a steady "pumping" action to the brakes, the idle rises and is smooth and steady. Could it be a bad check valve on the booster? Any help is appreciated. Thanks..

it could just be a bad booster it self. plug the line going to the booster and see if itll idle better

could also be a vacuum leak.

Hey Big,

I've already tried that, and it made no difference which led me to believe it my be the check valve.

Hi Tom,

Well, I already checked all the vacuum lines and didn't find any leaks. I don't see how pumping my brakes would increase vacuum throughout the whole system?

A clogged/leaking EGR valve can cause a rough idle.

Hey Swart,

Thank you for the input, but I did a lot of searching for answers prior to posting this question, so the EGR was already deemed ok by a mechanic. He couldn't find the issue either.. So let me ask my question again, would a bad check valve on the brake booster cause a loss of pressure and make the idle rough? I am only targeting this due to the fact as stated in my initial question, " when I apply a steady "pumping" action to the brakes, the idle rises and engine is smooth and steady. I guess I could just replace it and find out, huh... Thanks everyone for your help...

Should be cheap enough, just replace it and find out.

Or disconnect the vacuum line to the booster and plug it. See if the condition remains unchanged.

The booster uses vacuum to operate. Typically it wouldn't be enough to cause a fluctuation of engine RPM when releasing the booster, replenishing the vacuum in the booster for the next braking cycle.

And just because your mechanic has ruled out the EGR valve doesn't mean that it isn't the problem. Many people have cleaned their EGR valve only to have it immediately clog again with a chunk of carbon because they only dealt with the valve itself and not the EGR supply pipe or they didn't install a screened gasket to protect the valve.

^ which is why I suggested it could be a vacuum leak (inside your brake booster). Replace the check valve and see if that helps, if not it might be the entire brake booster.

Thank you all.. I will go over some of these things again. Tom, sorry, I misunderstood when you just mentioned vacuum leak. Thank you for speaking more specifically about what you meant.