AC compressor drags motor down??

[CptFantaztic]

Have a 2000 Tauras. Just had new battery and alternator installed along with tune up. Problem is that when heater or AC is on and I stop at traffic light the car drops idle erratically from about 900 and dips to about 400 and then jumps back up. I figure it has to be the compressor when it kicks on thats dragging the motor down. Any ideas?

[shorod]

So if you turn off the climate control at the traffic light does the idle still fluctuate?

The Idle Air Control (IAC) should increase the air flowing around the throttle plate to account for the increased load from the A/C, alternator, and power steering, when working properly. If the idle still fluctuates with the climate control turned off, I'd suspect your issue is due to a vacuum leak.

-Rod

[CptFantaztic]

It doesnt seem to affect idle when the A/C or heat is turned off. Only when ( it seems) that the compressor cycles on an off. Thought at first that maybe my battery wasnt big enough for the car ( which it actually wasnt, thats why I got a new one) The lights would dim also when the a/c kicked on. Have noticed a slight drop in rpm while driving but goes back up a second later when A/c kicks in. Thanks for your help.

[shorod]

Originally Posted by CptFantaztic

It doesnt seem to affect idle when the A/C or heat is turned off.

Hmmm, are you saying that whether or not the A/C is on has no impact on the drop in rpm at a light, or are you saying that you don't notice the drop if the A/C is off?

Do the lights still dim when the compressor kicks in, even with the new alternator and battery?

With the A/C off, what is the idle speed at the traffic lights?

-Rod

[CptFantaztic]

If the AC is off I dont notice any drop in idle speed at a stop light. It idles around 800 rpms and stayes pretty constant at the idle speed. If I turn the heater or AC on an pull up to a light, the idle speed will be about 800 rpm then it will drop from 800 rpm to about 400 rpm and then jump back to 800 rpm. I havent noticed the lights dimming since the new battery was put in. Its my wifes car and she hasnt mentioned it lately.

[shorod]

Since the idle doesn't drop with the A/C off that would suggest the either the compressor is close to seizing up or the Idle Air Control (IAC) servo is not effectively doing its job. You could further test the IAC by turning off the A/C with the engine idling and stopped, then turn the steering wheel all the way to one of the locks and hold it there for only a couple of seconds. If the idle speed drops like it does with the A/C, that further points to the IAC. Don't hold the steering at lock for more than a few seconds though as it is reportedly hard on the pump.

-Rod

[CptFantaztic]

Thanks. I will try turning the steering wheel and see what happens. I will do that Sat and post a reply. Thanks again for your help.

[CptFantaztic]

Had car in Park Idle was about 900rpm. Turned steering wheel left all the way and the idle dipped about 200 rpms and then when back up. Turned steering wheel right all the way and idle dropped to about 700 rpms that way too but then immediately came back up . Didnt leave it turned all the way cause didnt want to blow out power steering pump. Anything else I can try?

[shorod]

You could try the same with the car in Drive and foot firmly on the brake pedal, just like you would be at a stop light. A 200 rpm drop would seem to indicate the IAC isn't keeping up, but it might be even more obvious with the car in gear and that much more of a load on the engine.

-Rod

[CptFantaztic]

Thanks, I will give it a shot in Drive and see what happens. Again, Thanks

[mark_gober]

Any resolution on this problem? I've got a buddy bringing his Taurus over tomorrow and it seems to have the same problem.

Mark