erratic idle with A/C on

ctyclkr · 08-13-2004, 05:20 AM

1990 325is idles fine unless air conditioner is on, then erratic. example: at stoplight idle will stay at 1800-2000 RPM then may or may not drop after about 10 seconds to normal 800-1000 RPM. When RPM is high, switching off the A/C causes it to immediatly drop and idle correctly, turning on the A/C jumps the idle back to 1800-2000. This is erratic but happens 75% of the time the AC is in use. Shop charged me $275 for switch which did not fix problem, then said DME board needs replaced. I'm not so sure about going this route. Any help is appreciated. Thanks!

7hills · 08-13-2004, 01:41 PM

Steven,

Just went through the same thing with mine. TUrned out to be poor connections in the wiring under the intake manifold. There are three connectors that I cleaned with contact cleaner and put dielectric grease in before reconnecting. Idle has gone back to normal and the car runs better than it has in months. Don't know if this will help, but the grease is cheap and it would be a good first step.

ctyclkr · 08-16-2004, 09:31 AM

Thanks for the quick reply. Cleaned the connectors and re-seated, still had the problem. With the engine running at the high idle, I thought I would double-check myself on the connections and thanks to your reply, I quickly found the real problem. vacuum leak on both hoses going to the upper connector under the intake manifold. Now I can re-create the problem by wiggling that connector and increasing/decreasing the vacuum leak. I replaced one of the hoses and that helped, but I still have a leak on the other one, I think it is a special hose from the manifold to the switch, of course I can't see it or anything, and I believe I will have to remove the throat to replace it. Do you know what this hose is called so I can order it from Pelican ?

7hills · 08-16-2004, 05:35 PM

I am not sure exactly what it is called, but I am almost certain you could call Jared and he could get one shipped for you. Glad to at least get you in the right area to find the problem. I think I probably need to replace those hoses on mine - they are probably about ready to go at 170,000 miles.

sy5alive · 08-29-2004, 06:32 PM

DUDE i got the same exact problem. except my idle sometimes turn off the engine completely and is consistent. Also, when i turn off the A/C it just stops the engine as well. When i'm not idle, A/C works fine. I was just about to buy a new DME when I read your posts. Where can I find these hoses and connectors that both of you speak of?? I'm such a newb. But I'm trying to learn.

ctyclkr · 08-30-2004, 11:07 AM

The hoses I refer to are on the right side facing the engine, under the air intake. Pretty difficult to get to. I think if the hoses are leaking, it should make your idle faster, at least mine did. AFter I located the leaks and replace the hoses, the idle calmed down.

Check the electrical connections as well. They are prone to not making a good connection like is described in the reply to my post here, that helped my idle as well. Good luck !

Jared at Pelican Parts · 08-30-2004, 02:14 PM

I used to have this same problem on my car, it turned out to be just a vacuum leak from the breather hose to the throttle body.

ctyclkr · 08-30-2004, 03:24 PM

Hey, Jared. Are you talking about the big hose to the air intake where the throttle connections are? Sorry, but
I'm kinda a newbie on the names of these parts..