My '05 base with 150k started running rough on day when I was two hours from home. It would start and run fine for a few minutes, then start missing between 1,500 and 2,500 rpm. I got home by putting it in manual and driving it in 4th or 5th, depending on the speed. I considered fuel pump, coil pack, and finally injectors. Based on the symptoms, a visual inspection of the coils, and the cheapest course of action: I decided it was an injector. So, I ran a tank of premium and a bottle of injector cleaner through and it cleared up after about half a tank.

On to the next 150k miles!

 

Be aware that a lot of so called fuel injector cleaners are nothing more than ethanol in a bottle. 20 gallons of most fuels (regardless of octane rating) have 2 gallons of ethanol in the fuel already. Adding another 10 or 12 ounces of alcohol won't help anything. The fuel injector cleaners that are only alcohol typically say they contain alcohol on the label. If that's the only ingredient, it's not going to help you much.

Also, every gallon of fuel you purchase from ANY gas station, even the least expensive ones, has federally mandated minimums (some brands could have MORE than the minimum, but not necessarily) of fuel injector cleaners in them because the government learned real fast that clogged fuel injectors increase pollution. So even the discount gas you buy behind the liquor drive-thru has fuel injector cleaner in it.

One of the best ways to clean fuel injectors is to operate the car at wide open throttle for a couple of minutes, which will get real scary real fast if you aren't in the middle of nowhere when you do it. Pretty much any Cayenne is going to be at top speed after having the throttle wide open for a couple of minutes. This is a safer process if the vehicle doesn't achieve impressively high top speeds. I find anything over 140 mph is an impressive top speed! LOL

 

I agree, the Italian Tune Up still works wonders!