Celica Forums Classic Generations 5th Generation Celica Idle drops when brake pedal is applied

I've had this strange symptom for a few months now, but I can't seem to find anything wrong. This has been a trouble shooting nightmare. The idle also drops drastically when the a/c is switched on, the windows are rolled down, or I open the Sun roof.
I have replaced: all timing components, TPS, coolant temp switch, disty, cap, rotor, plugs, alt, battery, and installed my own grounding kit.
All the lights work, except courtesy door light switches, and this is driving me nuts.
Do you geniuses have any ideas?
Oh, and great job with Gen conversion over here.
Nice to see all of you, kinda, I guess...

my car car used to do that before i put my other motor in...as long as the engine doesnt die...your fine ...for the ac there sould be a black thing with a spring and a big skrew looking thing that you can adjust ...mine was way outta adjustment and the car would shut off if the car was idling below 600 rpm

it has something to do with your electrical system by lookin at your description did you check the fuses in the engine bay and the one inside by the stereo.. check it out

It sounds like a Vacuum problem. Common occurence in old Carbuerated cars. How heavy is it dropping hte idle, almost to the point of stalling? Check you brake booster and all the hoses.

Then again I have never really paid attention to my Celica's brakes... I am sure it is still a traditional Vacuum set up though.

Thanks, Murg. I am EFI, 91gt similar to Chaos. I will check all these things out, tough.

I am a self proclaimed Domestic Expert. I recognized your problem instantly, but as our cars are FI I am not certain as to what all transfers. I am still learning when it comes to Imports.

i thought at first this was a vacuum problem, but that doesnt explain the windows or the sunroof causing the same problem. i think its electrical.

the brake lights put a large draw on the system, as does the a/c, the windows, and the sunroof. the alternator has to work harder to keep up with this draw, and thats causing your idle to drop. If its not so bad that its causing your engine to stall, i would say dont worry about it- most cars will drop at least a little when a large load is put on them at idle, like headlights, or the afore-mentioned brake lights etc.

When I turn my A/C on it raises my idle.

Thanks all.
Very nice to hear from you again, Damsel. Nice to see you here as well.
My suspicions about this situation you have helped to confirm. If there were a way to boost amperage back to the battery, I think this would solve the problem.

thats normal- there is a high idle switch that turns on to bump the idle up, for exactly the reason i was mentioning before. The A/C puts a large draw on the alternator, as well as drawing power from the engine for the compressor, so it can drastically drop your idle if the engine doesn't do something to compensate. Hence, when you hit the A/C switch, something kicks on and raises the idle so that your engine has enough power to drive both of those things.

you said you just replaced the alternator? it might be that your new alternator isnt made to put out as many amps as the previous one you had, so its having to work harder to make the same power. Like i said, if its not to the point of killing your engine at idle, i wouldnt worry about it. If it is... just bump up the idle a bit

Have a load test done on the car. Autozone offers the service, amongst others. If the alt and bat test ok, I would suggest upgrading the pos wire between the alt and bat, and upgrading all major ground points.