Is anyone familiar with how to diagnose a bad power brake booster? I ran across a site with someone who had a rough idle on his 2.5l...he said that it took FOREVER to find (as is my case!!!) and turned out to be his brake booster. His brakes became weak, replaced the booster which also fixed his idle problem. I, too, have noticed that my brakes have felt spongy and weak for some time now, but I'm not sure how to test the booster. Is this something I can test with propane?


Oh, I ran my codes today (KOEO which I pull every month or so) and I'm getting a #23...MAT or manifold air temp. sensor. I'm wondering if this could cause a lumpy idle. The local parts stores (Advance and AutoZone) don't carry it for some reason. It looks just like a coolant temp sensor.

The mat is a temp switch.. When closed it tells the computer the engine is warm enough to go from the rich (startup) mode to the lean (run mode).

If you think the booster is sucking vacuume.. disconnect and plug the vac line to see if the idle improves.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

Jim, thanks for the reply... just plugged her and no difference so I'm guessing she's good.


You know, I was playing with the throttle today (manually) and I noticed that if I rev the motor and hold it, say around 2500, it'll hold the rev steady for maybe 2 seconds and then start to bog a little. If the MAT sensor was bad and the computer was thinking it was in warm-up mode (running rich), could this not cause the little 2.5 to bog since too much fuel would be dumped?

If I stomp on the throttle I also get the same type of bog/stumble. Man, I tell ya...as SOON as I finish school and land a job I'm buying a vehicle with a WARRANTY!!! I'll prolly still keep the Heep, as long as I can convince the wife. She HATES HATES HATES the Jeep!!!!!!!!! Just Empty Every Pocket!!!
I would also think I'd get a code specifically for "rich condition" but that's not the case. Hmm...

jmho...
I think I would start by replacing and / or repairing the item in question (MAT/P <img src="/forums/images/graemlins/shiner.gif" alt="" />)....

C.

Take a look at your plugs, wires, rotor and cap. Look for any rust or corrosion. How long has it been since you replaced any of these? May be do. <img src="/forums/images/graemlins/cheers.gif" alt="" />