When at stops, my 03 MCS idles between 800 - 1300 RPM, usually staying above 1000. If I turn on the AC, the idle drops down to 800 in about 15 secs. I've got several mods...CAI, 15% pulley, Nology wires and Denso IK22 plugs and a PowerChip. Car ran great for about 2000 miles with all mods before acting up. I've been to the dealer 4 times now and they are clueless. They've replaced the TB valve and tightened the PVC vacuum hose, only to have the problem begin the within minutes of leaving the dealership.

Anyone have any ideas about what could possibly be casusing this malady?

I'm taking the car in again next Wed. That want to reflash with V38, not sure this will help?

HELP!

 

If your car idles around 7-800 and periodically increases to about 1000 or a bit above and stays for aabout 15 seconds then goes back down for about 30 seconds and repeats this sequence it usually means that the ECU is raising the RPM because the voltage is dropping. The car speeds the engine (and the alternator) up to keep the battery from discharging. If you have a problem of idle 'hunting', where the same thing occurs but at a faster rate, it is sometimes caused by vacuum leaks. These are common around the intercooler boots, and also can be an issue if your PCV hose is collapsing.

 

GreatBear,

Thanks for the response...The idle only drops when I put the AC on. Also, the problem is constant for days at a time and then disappears for a day or two and the reappears.

 

Check you ground cables for any corrosion. If the system has a bad ground it can effect the idle of the car.