jmanuel

98 v6 accord. while coming to a stop as im braking my rpms slightly go up for a sec and car pulls forward before coming to a complete stop? if in park if i press on brake pedal rpm slightly moves around and lights dim. any ideas on what can cause this?

hondamark35

the brake booster works off of manifold vacuum. vacuum drop increases rpm. Idle control valve should minimize the vacuum drop, but doesn't necessarily eliminate it.

the dimming of the lights is probably the alternator no producing enough amperage due to low idle speed.

get the idle speed set right. do a tune-up. make sure the engine is in the best shape it can be before you continue to troubleshoot. Spark plugs, plug wires, clean throttle body, fresh oil, clean air filter... that sort of thing. also check that the IAC valve is not clogged or sticking.

jmanuel

raises it enough to make the car jump forward when braking? its a bit annoying.
car idles at 750 rpm
just put new oil and just replaced the iacv. this didnt occur till i chnged my valve cover gaskets

MAD_MIKE

Check for any vacuum leaks on the engine, look at vacuum hoses, PCV valve hose, Booster hose, gaskets for any false air leaks.

The air valve inside the booster may no be fully sealing inside the booster.
Normally when you depress the pedal when the rod moves forward in the booster the stored up vacuum in the booster pulls on the diaphragm which aids in pedal effort. As the rod moves forward a passage is opened to allow the backside of the diapgram to be at normal atmosphere pressure while the front stays under boosted(vacuum) assist. But if the valve is no longer properly sealing there will be a direct vacuum leak to the engine which will cause the engine to surge before sealing.

Test the booster by seeing how many reserve assisted pedal depressions you have with the engine off. Should have 2-3 full pedal assists.

Turn on the engine, allow full boost, depress the brake pedal and turn off the engine. Booster should be able to hold for ~30secs with no problems. If the pedal begins to push back there is most likely an internal leak causing a loss of boost assist.

jmanuel

okay so check for vacuum hose leaks and then with engine off i just press the brake pedal x3 and what should happen?

jmanuel

not really sure what a reserve assisted depressions is?
but if i press brake while engine on then shut off it should hold for 30sec before pushing back? and if that fails can it be fixed or better to just replace? thanks

MAD_MIKE

You should have near full boost assist for 2-3 full brake pedal depressions with the engine off.

You should also have the boost maintain assist with your foot on the pedal and the engine off. If the boost assist bleeds down you will loose the power brake assit and the brake pedal will gradually rise up as you cannot depress the pedal as low without the brake assist.

jmanuel

okay i pressed all excess vacuum out then pressed on pedal and turned engine on and pedal went down. then let engine idle for a minute to get full vacuum and then pressed on pedal and shut engine off and held foot on pedal for about 30 sec and took foot off then pedal came straight up? not sure if that was done correctly tho ha. heard you can disconnect hose and blow in it to check if its working also?

MAD_MIKE

Sounds like the booster is probably OK.
If there was a leak, and it did not hold vacuum, the booster would not maintain assist and the pedal would gradually push your foot back up.

Have you checked the booster check valve? It may be not fully closing. It should only allow air one way.

EDIT: Scratch that, if the check valve was bad the booster would not hold boost with the engine off. My mistake

holmesnmanny

I would take a good hard look at the brake booster hose. It could have a leak/tear that manifests itself when you press the brake pedal.

But like mike is suggesting this sounds brake booster related.

jmanuel

ill still test it to be sure.
should i just replace hose also??