1998 Cadillac Deville

landemartin · Posted at Sun Jun 28, 2009 10:48 pm

Engine Performance problem
1998 Cadillac Deville V8 Front Wheel Drive Automatic 124800 miles

Engine idles at 650 to 700 without air. With air on, idle speed fluctuates between 625 and 900 rpm. This is too slow to keep compressor running efficiently. Cycles on and off every 3 seconds.

Does this indicate a defective idler control sensor/relay?

gstacey · Posted at Sun Jun 28, 2009 11:10 pm

I would lean more towards an A/C concern, since it only happens with A/C compressor on. Possibly an under/over charge, or failing compressor. The fact that it does fine when the A/C is off leads me to think the IAC is fine. You have no stall, or high idle. It sounds like the load from the compressor is drawing it down.

landemartin · Posted at Mon Jun 29, 2009 7:06 am

Thank you for your reply. I just had a new compressor installed 11 months ago. And I had the freon level and the compressor checked last week. The mechanics told me they thought I needed a cooling fan (one wasn't working) and a new thermostat, so they installed these components. It didn't fix the problem.

gstacey · Posted at Mon Jun 29, 2009 9:52 pm

Does the system cycle normally when the engine speed is brought up? The fast cycle time usually indicates that the pressure is pulling down rapidly, either by undercharge or a restriction. Does it seem to cool adequately? If there was another fault that would cause the PCM to stop with compressor operation, it should have some ACM codes in the programmer, or stored fault codes in the PCM.

landemartin · Posted at Mon Jun 29, 2009 10:16 pm

Yes, the system cycles normally when engine speed is brought up. The mechanic said the system is full of freon.

There is a Service Engine Soon light on, but I don't know what codes it is returning.

I took off the AIC controller this morning. The plunger had black soot and grease/grime all over it. I cleaned it off with a cloth and squirted a dab of WD-40 into it and replaced it. After reinstalling it, the engine seemed to run about 50 rpm faster than it did before. The compressor didn't cycle but once every minute or so after that; however, the outside temperature was considerably cooler today than the other days I've been testing it.