I have a bit of an idle problem. When I come to a stop, idle is at 1100 and falls slowly (when the engine is warm). If I pump the brake a couple times, it goes up to 14-1500 and then falls down to 5-600. One of my buddies told me I probably had air in my brakes and they needed to be bled. I checked for vacuum leaks and didn't find any, so I was wondering if this was really a possibility (I thought it was the IAC going bad). Thanks!

First you must understand that air is compressable, brake fluid is not. Therefore when you have air in your brake system, it compresses it all which is the primary cause for "spongy brakes". So if their is enough of air in the lines(which is entirely possible) and you press your brakes, the booster cant supply enough of pressure so it draws extra vacuum from the engine which can cause it to chug and in extreme cases, turn the engine off completely.<---this happened to me once. Hope this helps you!!

C'mon, people, any thoughts?

My car idles up some if I pump the brakes or turn the wheel. I believe its just because you are putting more strain on the motor and slowing it down so the ECU raises the idle some. I think mine only goes to about 1200. Not 1500-1600 like you said. You could check the IAC sensor. It wont hurt anything.

98 Eclipse GS Turbo
Built motor - MS2 - Holset hy35 - Zoom Stg 4 Clutch - 57.5mm TB - ARP Headstuds - Turbonetics wastegate - 3" Turbo back - FMIC - Greddy RZ BOV - Walbro 255 - 650cc Injectors - Fidanza Flywheel - Cobra calipers w/ 13" Rotors - Oil Cooler - DevilsOwn meth injection

1981 Chevy Scottsdale
1987 Nissan 300zx - Chump Car
2001 BMW 325i

Im not sure if this is relevant but...

My car used to idle very oddly as you describe. It would run fine but anytime I would let out the clutch and cruise to a stop the rotation speed would increase to 2000 rpms and remain there for a few moments. I first thought this was due to the inertia of the flywheel but after thinking about it some more it would not explain for the great increase of rpms.

I noticed that It wasn't heating up one day and replaced the thermostat to find that it was the problem the whole time. The thermostat was stuck open and wasn't allowing the engine to reach operating temperature. The ECU was getting a signal to add more gas bc the temp was low and it was essentially set to "full choke" the entire time. This also would cause the car to stall out when sitting still but once I replaced the thermostat it ran like a dream.

sounds slightly normal. the engine should compensate for the extra vacuum required for the pumping of the brakes and increase the idle slightly. the sudden dropping of the idle afterwards is the curious bit. your IAC might be getting old and adjusting too far in and out, but that's tough to diagnose

when your friend said that your brakes need to be bled he meant getting air bubbles out of the fluid, not to look for vacuum leaks

hope this helps

Erik P.
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