Hey guys. I'll keep this short and detailed. A few months ago I started having high idle issues. Generally it would surge from 900-2000 like a pulse every 2 seconds. I checked for vacuum leaks, everything's good. Swapped the throttle body, didn't help. I kept an eye on my voltage meter and noticed when the cooling fan comes on, the voltage drops to around 12 volts (idle starts to drop) then that's when the idle starts pulsing high and the voltage returns to around 14 volts. I thought about replacing the alternator, but given it's so damn expensive, I figured I'd see if anyone else had some input or ideas of what could be causing the issue. Maybe some kind of regulator for the cooling fan? It's almost as if it's drawing to much power and causing the issue. Any thoughts or feedback is much appreciated. Thanks guys.

 

I can't say this is completely normal, but I know for certain its normal for the charging system voltage to fluctuate more than you think it should.

Have you scanned the DME for error codes and fuel trim values?

 

It's running a code. I can't remember the number, but it's "unexpected high idle". I know the voltage will fluctuate, but what it's doing isn't normal. It idles fine, then when I'm stopped in traffic and the fan comes on the voltage drops to 12 and the car feels like it's about to stall. That's when the idle goes high and starts "pulsing" from 1000-2000rpms and the voltage returns to 14.

 

How old is the battery? Maybe low output is causing weird voltage spikes. Or maybe the voltage regulator is going bad.

If you have a volt meter, see what the voltage is while the motor is running. It should be between 12.5 and 14.5 volts.

Maybe trying getting the battery load tested or just charge the battery and see if that helps. If the battery checks out, get the alternator bench tested.

Or maybe just a simple battery terminal cleaning is all it needs.

 

Well, I found the problem. After almost six months of battling this high idle and countless attempts to figure out the cause... I finally found it. My last attempt, before buying the ridiculously expensive alternator, I thought I'd might as well try changing the serpentine belt. The old belt looked ok when I took it off, but I noticed something else. I found a very thin piece of an old belt (I'm guessing previous owner had one break while driving) wrapped around the ac pulley. It was about a foot long. I carefully removed it and replaced the old belt. Walla... Engine light went off and car idles perfectly. My guess is that the piece of old belt wrapped around the ac pulley was causing enough friction at idle to slow down the belt. Then my computer made up for it by increasing the engine speed. I doubt this is a common problem, but if anyone else has a high idle and voltage issues I recommend checking the belt and pulleys!

 

Nice fix!

PS it's 'Voila'. It's French.