Step on brake at idle, RPM drops?

[TurboGeoff]

Whenever i step on my brake at idle, the engine Revs drop from 750 to 700 or lower, i thought it was the fuel pump, so i got a walbro 190 and reqired it, same problem, is this a common dsm thing, or something else?

-Geoff

 

[ab0tj]

Automatic or manual? Could also just be the power brakes bogging the engine down a little.

 

[rowlex]

I am not certain but i believe our brake's are somehow linked with the car's vacuum. Check for boost/vacuum leaks, check and make sure the BISS screw is still there.. Then if that stuff is ok just up the idle using the BISS screw

 

[TurboGeoff]

Of course BISS screw is still there, and im a manual.

Upping the idle doesnt change anything.

When i step on the brake, voltage drops too, i can hear teh fuel pump change tones, and lights dim.

 

[Lordpaxin]

if none of the above mentioned stuff was valid, i would suggest a electrical problem, not really a problem, but the load of the brake lights drawing the system down.

alternator, or a weak battery.
check and see if there is water in your battery.

at idle, get a volt meter, and check the voltages on the battery, and the batter cable from the alternator. a differce would indicate a bad connection, and explain the problem

 

[TurboGeoff]

Ya im gunna try that today.

 

[CarTrader29]

My 1990 GSX does this as well as my 1990 Talon TSi. I think its normal but dont quote me on that. If something is wrong I'd like to know why....

 

[RedRain]

It is normal if u r dropping about 25-50 rpm's since the Brake Booster is using engine vacuum to assist you in braking.

 

[Defiant]

It's drag from the alternator powering up the brake lights. To test, disconnect the brake light switch, or pull the brake light fuse and try it.

 

[98spydert]

Unplug the break booster vac hose and cap off the nipple and try again at idle (don't go anywhere like that). If that's not it, test your battery/check the water if it's not sealed, clean the terminals, and make some new fresh ground straps for the engine and battery. Good luck.

 

[Punkloser6]

FINALLY thank you someone gave me something that has a solution to my problem!! THank you LORDPAXIN i hope yer info will help me but thanks for ACTUALLY answering the question it sounds like it would work for me thanks! im going to try it tomorrow

 

[MyBeatGSX]

It's drag from the alternator powering up the brake lights. To test, disconnect the brake light switch, or pull the brake light fuse and try it.

Why are these alts so weak? Mine was replaced a couple years ago and I have a brand new battery with way excess CCA and my cel dims in time with the turn signal. I've never seen such a weak alternator in any car, or maybe its the horrible factory ground system....