Engine stalls at idle when A/C on

UnSafe · 09-05-2007, 04:05 AM

Still getting the bugs worked out on my wife's '78 911SC. There's a bunch..

When the A/C is on and I let off the gas, like at a stop light, the engine stalls. I searched and could only find info to suggest that an overfull/ overpressure system may create excessive drag and cause this. Not sure if I can use a tire gauge to check system pressure or not.

Any thoughts, ideas or solutions welcome.

Walter_Middie · Walter_Middie's Garage

Engine stalling after letting off on the gas is a sign of running rich.

JBO · 09-05-2007, 06:41 AM

You may just need to increase the idle by 200 rpm's during the summer months when using the A/C - these cars don't auto. increase the idle when the A/C is on as most cars do. I do this then turn it back down to 950-1k rpm in the fall. If it does it with the A/C off or hunts for idle, as Rex says that may mean it is running a little rich.

UnSafe · 09-05-2007, 05:38 PM

Thanks for the input.

I don't think it's running too rich, it only occurs when the AC is on, but will search for rich/ lean diagnostic stuff. It drops to a consistant and smooth idle when the AC is off.

As for adjusting the idle up a notch, is it simply a throttle stop screw adjustment, or something more involved? My Bentlys book is in the car right now and my wife is out driving it.

Scott R · Scott R's Garage

Quote:

Originally Posted by UnSafe

Thanks for the input.

I don't think it's running too rich, it only occurs when the AC is on, but will search for rich/ lean diagnostic stuff. It drops to a consistant and smooth idle when the AC is off.

As for adjusting the idle up a notch, is it simply a throttle stop screw adjustment, or something more involved? My Bentlys book is in the car right now and my wife is out driving it.

Could be the compressor going out, if it's the OEM York the bearings and pistons start to seize over time, if the system was not evacuated correctly and water is mixed in with the oil. How hard is it to turn the outer wheel by hand? This was the case with mine, had been sitting exposed for a while and started to rust, they can be rebuilt DIY for a small amount of money.

Paulporsche · 09-06-2007, 04:23 AM

Unsafe,

Don't mess w/ throttlestops for rpm adjustment. Check the Bentley's or this BB. Use the large flat screwhead @ the side of the throttle area.

UnSafe · 09-06-2007, 03:04 PM

Thanks all. Found the appropriate idle adjustment screw and was able to adjust with fingers. Idles just a hair under 1K RPM and no more stalling!

Now on to the other 49 bugs to fix....