Missing once again

[robroy55]

Hi Folks,
I had the ignition coil replaced because of the car missing quite a bit. All was well. I don't use the Air much but now, when I put the Air on, at an idle, the car misses a LOT. It is a 2002, 37K 24 valve Duratec. Any suggestions on why it misses once again ONLY when the Air is truned on??

Thanks again for all your past help!!
Rob Roy

[shorod]

Originally Posted by robroy55

Hi Folks,
I had the ignition coil replaced because of the car missing quite a bit. All was well. I don't use the Air much but now, when I put the Air on, at an idle, the car misses a LOT. It is a 2002, 37K 24 valve Duratec. Any suggestions on why it misses once again ONLY when the Air is truned on??

Thanks again for all your past help!!
Rob Roy

Are you sure it's actually missing, or is the engine speed just dropping a lot? Does your car have a tachometer in the instrument cluster? If so, watch what happens to the engine rpms when you turn the A/C on. Does it do the same if you turn the defroster on (which also uses the A/C compressor and clutch)? If the rpms are dropping significantly, your Idle Speed Control (ISC) servo may not be functioning properly to compensate for the added load of the A/C compressor.

With the A/C off, you might try turning the steering wheel all the way to lock and see if the engine feels rough. If so, I'd definitely suspect the ISC.

It may be that the passages for the ISC or the throttle plate are just caked with carbon/sludge.

-Rod

[robroy55]

Originally Posted by shorod

Are you sure it's actually missing, or is the engine speed just dropping a lot? Does your car have a tachometer in the instrument cluster? If so, watch what happens to the engine rpms when you turn the A/C on. Does it do the same if you turn the defroster on (which also uses the A/C compressor and clutch)? If the rpms are dropping significantly, your Idle Speed Control (ISC) servo may not be functioning properly to compensate for the added load of the A/C compressor.

With the A/C off, you might try turning the steering wheel all the way to lock and see if the engine feels rough. If so, I'd definitely suspect the ISC.

It may be that the passages for the ISC or the throttle plate are just caked with carbon/sludge.

-Rod

_____________________________
Thank you for your suggestions. The engine is missing and not just droping in rpm's when the air is truned on. When the air is truned on, the rpm's only drop 1 mark on the guage. Turning the wheel all the way to the right makes no difference in the missing problem. As soon as I start off (with the air ON) all runs smooth. With the air off, the car only misses once every 30 sec or so.
Thank you Very Much for your help and suggestions?
I am thinking that maybe the ignition coil that was put in may be diffective?? Any thoughts on that??
Rob Roy

[shorod]

Inspect all your plug wires an make sure a vacuum line didn't get knocked off in the process of replacing the coil.

Also, if the car is in fact missing, your computer should be able to read this as a misfire. If it is infrequent enough that it doesn't cause a CEL, the Readiness parameters for emissions should at least record misfires for the individual cylinders. A good scan tool should be able to indicate which cylinder(s) are misfiring and likely narrow your search a bit.

-Rod