bobbing idle while braking

[knowleqe]

hey everyone, my problem is this: whenever i start braking lets say in 5th with the clutch in, my rpms will dip to about 200-500rpm w/the AC on. if i were to go to neutral, THEN, brake the idle will stay at 650rpm. but if i brake and have the clutch in at the same time is when the rpms will dip dangerously low.

i am going to remove and clean the IACV valve this coming tuesday and change the O2 sensor since i am also getting bad mileage, 150mi at half. the vacuum lines coming from the intake are all secure. what do you guys suggest that i look into?

thank you

[atcq110]

150 at half tank is not that bad, its about 25mpg. I would check your alternator. Do your dash lights dim when you hit the brake?

[bcar240]

what happens if you are stopped in gear with the clutch in and the brake down? What happens if the A/C isn't on? If you mean you get 150 miles when the needle points to 1/2 then you are doing pretty good. I can get nearly a whole "1/4" out of the tank after I pass E. If you are concerned about mileage do a test by recording the odometer when you fill up your tank, drive some and then fill up again noting the amount of gas you used. Then check your odo again and find the miles you drove and divide the miles you drove by the amount of gas you used.

[180fan]

have you checked the one way valve connected to your brake booster?

[knowleqe]

have you checked the one way valve connected to your brake booster?

thanks 180fan for actually trying to give me a solution. can you show/tell me where the valve is?

thanks

[bcar240]

well, if you want a solution, also check the following:

IAAIACVvacuum systemMAFSTPSgrounding wires/electrical connectionscoolant temp sensoro2 sensora/c compressor function

amung about 1000 other things that can cause low rpms and / or bad idle. Just tryin to get some facts first. (although the brake booster check valve would be a good place to start considering the circumstances, good call 180fan.) The valve in question is in the big line running to the brake booster, and has tubing clamped on each side. Here is what the FSM has to say about the check valve, notice the cool diagram!

[driftaholic]

i was gonna suggest vacuum realated stuff too..

god i love those pics from the fsm....looks like he's doin drugs or something. it's great

[s13EastTN]

Mine does that too. I replaced the clutch fan with electric ones, which caused my idle to drop down a little bit. So I upped my idle and viola, problem wasn't a problem any more. It still does it, but never goes below 600 now, even with everything turned on.

[180fan]

lol that picture is hilarious. looks like he's got a hash pipe taking a puff