GhettoRS

So everytime I am idling at normal operating temperature and hit the brakes, my 90GS's idle dips and the car mildly shakes. It never shuts off, it never bogs or does this while driving. Only at idle, and the more electrical load I put on the car the worse it gets. Headlights - Drops a bit. Defroster - Drops even more. Depress brake pedal - Drops even more.

The car operates perfectly otherwise. Tons of power and runs like a top. This problem is driving me nuts. I have checked and re-run engine and chassis grounds and completely uninstalled my alarm system and stereo but nothing changed.

Any ideas? Im lost.

Thanks

D.A9 GUY

the brakes,lights use power from the motor to operate ..but shouldnt cause that bad of problems ..like if i sit a hit my brakes i can see the rpms go down 50-100rpms this is normal a caused buy the brakes strain on the motor unless ur motor is stalling or running really rough and i talking bogging ect then your fine this is normal if you hit the brake continually and the car stalls then problem !

Solster

If the power pull from your brake lights is all it takes to bog your motor you have a Major electrical problem.

the reason for the bogginh of the motor is from the brake booster. when you press down on the brakes the booster uses vac from the intake to help apply force to the brake system.

when you hit the brakes and the engine is at idle you change the pressure in the intake and the ECU make changes to counter act the drop in pressure. making the engine bog down a little.

it's normal unless the engine stalls out then you need to lookinto geting the booster or the inline oneway air valve replaced.

GhettoRS

Well, to be clear no matter how much I hit the brakes the motor will not stall. It just bogs it down a few hundred RPM's and then the car shimmies/vibrates. That is as bad as it gets.

Now it is possible that the shaking is happening because of the 22 year old engine mounts but, I just get the feeling that something electrical just aint right cuz I have a had a lot of problems with all things electrical since I got this car.

Like, its not just the brakes that make the RPM's dip, can be sunroof, defroster anything with a load.

Thanks for the help guys, any suggestions are appreciated. Its time like these I sorta wish the car wasnt stock so I could have a whole lot less wiring to check. :S

GhettoRS

UPDATE:

If I turn on the blower fan at the same time as the headlights the right side dims to half brightness and the corner markers and fogs glow dimly. I have the DRL Relay removed so I know it has nothing to do with that. I have checked the grounds in the engine bay and they all seem fine.


I am guessing a wire is grounding out somewhere. Any thoughts on where to start looking?

Thanks

Solster

keep in mind the electricity is like a Car and the wire is the road it flows ON the wire not through it like water in a pipe. so if the connections look corroded pull them off and clean them.

also there is a grounding point mext to the drivers headlight, passenger headlight (the support between the rad and headlight) the passenger strut tower and a main ground under the battery tray. they look like plastic boxes with a metal bracket on the top and all black wires out the bottom.

might also have a Weak alt so see what kind of voltage your getting at the bat when the car is running. it should be 14.2~14.6 volts. then turn on the headlights, heater fan at max and rear defroster voltage should be no less then 13.2 if your seeing lower volts your alt is going out. if you at any time see volt over 14.8 your alt is alread bad and you need a new one before it fries your ECU and or other electronics.

GhettoRS

Thanks for the reply Solster. I have indeed removed and cleaned the contacts for each ground. I even put an extra 4 gauge ground from the batt terminal wire to a solid grounding point in the car but no difference. I also did thoroughly test the alternator a few months back by removing it and bringing to a local guy to bench test. He said it was fine.

Im thinking that because the running lights glow dim on the right side when I turn the blower fan on, regardless of whether or not the DRL relay is in, tells me that there is something wrong in that one of those circuits. Im not expert, just seems logical.