Idle With Airconditioning On

[stlmaj]

I have an 03' Sierra 1500HD crewcab, 6Liter engine and 90K miles. The truck idles fine with a/c off but when turned on it drops down to and surges between 200 - 400 rpm untill it stalls. The a/c blows warm and the a/c compressor clutch is not engaged. If I hold the idle up to 600 - 1000 rpm the a/c compressor kicks on and blows cold? It does it in park, drive and nuetral. The engine temp doesn't seem to matter, it does it both cold and warm however seems worse when warm (aprox 190-200 degrees). I replaced the spark plugs and wires with no change in the problem. I have had an occasional MAF sensor fault causing the check engine light to come on so I cleaned the screen but have had no change in the airconditioning problem and the check engine light has not been on since I cleaned it; but it's only been a day. Please help....

 

Thanks in advance,

Matt

[stlmaj]

Ok this afternoon I was having idle problems regardless of a/c on or off. I think the a/c not working is just a symptom and not the problem because the a/c works whenever I have rpms above 500 - 600. So any ideas as to what is causing the idle to drop? I am going to check for a vacume leak tonight. I have a scan tool that lets me see real time data from all the sensors I'm just not sure what I am looking for. I did not notice anything unusual with the scan tool connected?

 

Thanks in advance,

Matt

[redvett]

With your scanner look if A/C is enabled and IAC counts increases. IAC counts would go up if the A/C signal is going to the PCM and with A/C off in drive you should have 15-30 counts.

[stlmaj]

Ok, this took awail but I got it figured out. The problem was coking or carbon build up on the air inlet butterfly... I cleaned it off with some contact cleaner wiped it clean reinstalled the plastic air intake line going to the filter. Now it with A/C on runs and idles like normal. Man what a pain. Sure am glad to have it fixed!

 

Hope this information helps someone else.

 

Good luck,

Matt