A/C droppin the rpms like a mofo

[Nstyle29]

Alright my prob is when i turn my A/C on it clicks on and then my rpms will go from around 600 to 200 then it immediately clicks off then the rpm goes back up to 600 then it clicks on and it drops it to 200. At one point it killed the car. That is at idling. At higher speeds say 30-40 mph my car lurches every time it kicks on and if i am speeding up from a light and it is on it takes more foot to the pedal and then it will click off and i take off like a bat out of hell wihtout meaning to. Any idea?

[macder]

I have the same problem and it's ussualy caused by a faulty ISC. The AC compressor takes a nice amount of power from the crank and the ISC is supposed to regulate it by opening up the throttle more to compensate your idle speed. Loosing a significant amount of power is normal in any vehicle w/AC turned on since the compressor is driven by the crank through a belt. If you don't want to replace your ISC, you can raise your idle by either adjusting you BISS screw or adjusting your throttle cable. If you don't want your idle to be to high without the AC just turn it off when idling (Which is what i've learned to live with) or replace your ISC. The OEM part # for the ISC is MD628051 listed @ $275.33. I've heard that the OEM part will fail sooner then later, but search around as there as improved aftermarket/3rd party applications.

Search this forum (google will bring up results as well) for idle problems, this is a common problem among DSM's w/4g63's, no shortage of info on this topic.

[l_eclipse_l]

I try to leave the A/C off when I'm driving by myself, just roll the windows down, but the bitches always complain, so I end up giving in. That damn A/C sucks power and gas, two things I always need more of.

[kjewer1]

If idle with the AC off is really 600, then thats a good bit too low as well. The ECU targets 750 on 5 speeds, and I think its the same on autos. The lower it is before the ac comes on, the lower it may go with the ac on.

[Nstyle29]

yeah i haven't had it on in years cause i unplugged it and the nebraska 105-110 degree weather is too much anymore. When i want power i just click it off, but i will try and mess with the biss screw...its on the TB isn't it? Stuck about half an inch or so below the metal cylinder it is in isn't it?

[macder]

The BISS Screw is on the throttle body, it pretty noticable, it also may have a cap over it and like you said it sits inside a small cylinder. Turning counterclock wise raises idle, vice versa. Carefull not to loosen it too much as it may pop it out and that will cause problems. I usually turn it in 90deg incriments. A basic trial and error procedure

[fiberglasscivic]

if the ISC isn't a problem I would check the compressor. If it's gone bad then you would notice similar problems.

[kjewer1]

To clarify, changing the BISS position does not change idle speed, unless the ISC has failed or is at the end of its travel. The ECU will ALWAYS try to keep idle at the target idle speed, in the case of the stock ECU, 750 rpm. The BISS adjsutment is to get the ISC to the center of its range. Just like we adjust the low map on the AFC to get fuel trims in the center. The exact same concept. THe BISS may change idle in the short term, but over a few minutes the ISC should pull idle back to 750 if its working properly and not maxed out.