Idle drops significantly when a/c on

[drewbuddy]

when i turn on my a/c at idle it will drop almost to the point of stalling. Even when I'm driving rpm drops but not to the point of stalling out,( cause I'm driving and rpm is up). Don't here any abnormal noises, clunks, squeals, ect..Never had it checked out, only guessing when I say maybe a plug in the line, maybe pump is shot? It does blow cool air, not cold. It is a '91 2l turbo, not sure if replacement is necessary or if a plug needs to be freed up or what. If anyone has any suggestions or ideas for me to check out it would be appreciated(car is not running, in the midst of an attempt at rebuild) Thanks for any help

 

[Jon91TSi]

Sounds like a problem with the ISC motor, BISS adjustment, or failing alternator. Do you have access to a datalogger?

 

[drewbuddy]

no, to check for codes i use my multimeter

 

[Jon91TSi]

You need a logger to check the ISC steps that the ECU is seeing, as well as voltage at the ECU at the time the A/C is turned on.

 

[c2ypt1c]

Sounds like a problem with the ISC motor, BISS adjustment, or failing alternator.

I'm leaning more toward the BISS

 

[drewbuddy]

I will ask around see if I can track one down, Thanks Jon91TSi

 

[Jon91TSi]

I will ask around see if I can track one down, Thanks Jon91TSi

You bet, Idle should be around 30 steps warm and in neutral, it should go up slightly when the AC kicks on. Let us know what you find. If the ISC motor isn't anywhere near 30 steps you need to adjust your BISS per the vfaq and then try the A/C again and see what happens. The BISS adjustment and ISC position go hand in hand.

 

[drewbuddy]

Ok so I might sound like a dumbass, but I'm still learning here and dont know what BISS stands for or is, can't find it in my manual

 

[Jon91TSi]

Ok so I might sound like a dumbass, but I'm still learning here and dont know what BISS stands for or is, can't find it in my manual

Base Idle Set Screw. That's the little guy on top of your throttle body, TPS (Throttle position sensor) side.

The only dumb questions are the ones you don't ask.

 

[drewbuddy]

yes, the manual calls it the speed adjusting screw, thanks again

 

[eclipse420ags]

Ive got a few small boost leaks and it does that with me to.

 

[mattasi]

Do a boost leak test. Boost leaks can really throw off your car trying to idle with different loads.

 

[drewbuddy]

or is this the screw your talking about?

i will figure how to do a boost leak test.
It doesnt do it under any other operation or loads

 

[MiroDSM]

A little up towards your fingernail and to the right. That yellow/orange thing

 

[Jon91TSi]

or is this the screw your talking about?

i will figure how to do a boost leak test.
It doesnt do it under any other operation or loads

Right above the tps, to your right in that picture, it's a recessed screw. The screw you're pointing to is for a bracket for the throttle body elbow.

Also, those unused ports on top of your throttle body need to have vacuum caps on them, otherwise you've created a vacuum/boost leak.

 

[drewbuddy]

engine is apart, this is sitting in my trunk, ring lands separated on my #3 this is why the attempt at a rebuild

ok so the reason i didn't see the screw is the orange stuff you see in the pic was silicone or gasket goo or whatever it was covering it up, didn't even realize a screw was there. just went looking for the screw and picked it out of there and yup there's a screw. Thanks guys

 

[mattasi]

or is this the screw your talking about?

i will figure how to do a boost leak test.
It doesnt do it under any other operation or loads

You really need to do a boost leak test. At full throttle you may/maynot notice anything wrong with the car. It is at idle that you really notice the effects of a boost leak.
2G Turbo DSM Boost Leaks -How to test and fix

 

[drewbuddy]

thanks mattasi