rpm's drop when i turn a/c on why?

[tfaulk21]

my car runs fine until i wanna get some air becuase its about 95 degrees in that car with the windows DOWN ONLY thing wrong is when i turn on my A/C my rpm's drop drastically a couple times it's made my car shut off while i'm driving they get so low. almost made me wreck. looking to get that fixed thinking it's some kind of sensor but considering i'm a nube to the dsm and mechanic world i think some of you guys should give me a proffesional opinion

thanks
-tyler

 

[Bud92gsx]

Your adding another load to the belts/engine..So the rpms should drop maybe 200 rpms..

 

[Nasty Dream]

RPM drop at idle is normal, but they should climb back up on their own after a moment. Maybe not all the way, but enough to maintain idle fine. Like bud says, you will feel the load at idle. Lights may even dim.

But the engine stalls while you are driving? Are you sure you are remembering this right? That would be some kind of problem.

 

[tfaulk21]

yeah man the car cuts off i've had it for about a year and its always done it just havent gotten around to the problem till now but i know its suppost to drop but not shut my engine off the only time i can run the a/c is on the high way because the rpms are running at about 4k. say the a/c is on and i'm getting off the high way i mash in the clutch and boom rpm fly down to 0 man and the car shuts off i think there's suppost to be a sensor saying "hey you have some more load i think its time to raise the rpm" (not literally for those who take things seriously) or so what i've been told there is a sensor that does that.

 

[Anubis_4_99]

mine does this as well, if i crank the wheel while it does it will die, but normally it idles down to 450-500ish and stays there. never comes back up. and doesnt cool at idle either.

 

[herms99gst]

Yes your rpm's will drop when your ac is turned on bc of the added load, but you shouldnt stall. What is your base idle with no accesorys on? I would start looking for a vaccum leak, it may not be too noticeable with no load on the engine.

 

[tfaulk21]

yea your right mr. herm99gst. i'm thinking cold start 1200 and normal 750? somewhere around there.

 

[KAOI]

Typically anything that using a load from the engine will cause the rpms to drop. next time youre in the car and the car is idling steadily turn the steering wheel, youll notice the rpms drop very slightly. This will happen when you turn the headlights on as well.

 

[ReYnd]

Turn the AC off quickly to avoid stalling until you get it fixed. My brother's Laser had that issue for a while until he quit driving it. Now I've gotten into them, I think the IAC motor may be to blame (as it is for many cases of idle surge, as well). Perhaps you do have a vacuum leak though. Or the TPS needs adjusting. Your cold idle is a tad high and warm is a little low.

 

[herms99gst]

And yes your iac will cause this if its not functioning correctly, its what tells your car to adjust rpm in relation to load....id also check to see if your throttle body needs a good cleaning

 

[tcbikerguy6]

That is all normal. I'm not sure why it would kill the car. What do you normally idle at?

 

[herms99gst]

He said 750 warm 1200 cold, that sounds about right to me.

 

[uberswede]

Not sure if this helps at all, but with my A/C on, if I let the revs drop freely from 3000rpms or more, the car will stall... Then again I've got almost all light aluminum internals, so I've got next to no momentum and the revs drop QUICK.

 

[BigBeans]

The idle control motor should compensate for the increased load almost instantly, if it doesn't it either isn't functioning properly or it's maxed out and the BISS needs to be adjusted to get it back in the normal operating range.

There's plenty of info on here about BISS adjustment, just do a quick search

 

[tfaulk21]

also when its cold mainly last winter when i got the car it would rev up and down when i crunk it up. from 1200 to about 1400 and every second it seemed like it would drop rpm raise drop raise idk if thats connected to the a/c problem but when i do cut the a/c on and it doesnt stall the it shifts like that from about 200 to 400 just barely enough power to keep it going thats at idle though if i hit the gas it will go up of course.

 

[herms99gst]

Get a new IAC.

 

[tfaulk21]

alright i'll see how that goes it wouldn'tt be a bad idea to replace anyways considering it's the first one on the car so thats what nearly 19 years or so. if anybody still has any input or ideas what it could be please tell.

will a 94 models iac fit on a 93?

 

[DSM1G90]

Small lessons on AC equipped vehicles: When you have the defrost on, the compressor kicks on also so the fluid can still do some circulating.

Now, you got an 18 yr old vehicle there and the compressors don't last forever.

I bet the compressor is gradually wanting to seize up on you why the drastic hints of wanting to stall out with it putting tons of pulley resistance causing the motor to stall on occasion. If can, take the belt off the compressor and see what happens if any more of these issues arises.

(course also, removing the aircan which is sucking in the hot air from under the hood intead of the cooled air as it enters the air can via the snorkel, can also cause irratic A/F mixtures..)

 

[spritian]

It has to do with the idle switch and the maf not able to compensate. The only real way I fixed this was with dsmlink.

Essentially when the idle switch gets active, and the Rpms drop, airflowperrev should drop too but most of the time it doesn't, causing the ecu to dump more fuel in which bogs the motor or even stalls it.

Here's the ecmlink article that describes it in detail.

http://www.ecmtuning.com/wiki/idleair