Playing around with my wideband O2 sensor tonight, I noticed a funny occurance at idle. Car idles at a perfect 14.7, but I noticed if I pumped the brake pedal more than a couple times, the AFR's would shoot lean while I kept pumping the pedal. The AFR would reach about 20:1, idle would get a little rough, and then would return right back to normal after pumping stopped.

My question is if this is normal?? I can't say I know exactly how a vaccum assited brake booster works, but have never noticed anything like this in any of my other cars. First thought is a vaccum leak????

Here is a screen shot from the data log..... as, you can see AFR is flat, start pumping the brakes, AFR goes lean, stop pumping and goes back to flat.

http://lh3.google.com/spencerbunting/Rte783fkEQI/AAAAAAAAADA/X-t_fVKyQAM/s800/untitled.JPG

Since air is going to enter the booster when you pump the brakes it wouldn't be surprising to see that cause leaning out of the mixture at idle.

yeah i guess this is normal, use to do this on most of my cars, playing on the brake pedals during heavy traffic and notice the rev going up and down. cool huh!

Try turning the wheels left and right, lock to lock. Notice any difference?
Lyon

is there vaccum hoses linked to power steering ???

Try turning the wheels left and right, lock to lock. Notice any difference?
Lyon

What would that indicate??

Again, I don't know how a booster exactly works, but doesn't it use air/vacuum from the engine when it is working? So in theory, when pumping the brakes, it is taking post-HFM (metered) air. In theory, this would create a rich condition, since less air is going into the motor. Just a thought.....

I just don't understand how an excess of air is entering the system. First thought to me is vacuum leak....?

The booster likely has a leak, only during use. Does your idle rpm go up when you pump the brakes? Does the brake pedal get harder after multible applications?

This really is nothing and borderlines on normal. It won't affect your performance driving unless your booster failes out right and the vac leak is much worse. If its an original booster failure is likely.

Booster failure immenant. I had a Lumina that had the booster go out and when you stepped on the brakes the rpms would go up. A real bitch with the auto trans, it was like stepping on the gas while trying to brake.