Contour Enthusiasts Group Archives Forums Modifications Zetec Maintenance Idles great in Neutral but horribly in Drive??

I've been trying to work out a bad idle problem and I noticed today that if I shift the car into neutral (automatic transmission), my car idles great at around 800 RPM, smooth & quiet. But when I shift the car back into drive, the idle immediately drops to around 500 and the car starts shaking and vibrating. Back into neutral and the idle goes back up and everything is smooth and quiet again. Any ideas? Thanks guys.

You'll want to look into three to four different things first. First, clean the MAF. Many good posts on that subject so just search for that. Second, clean the IAT. Search for that as well. Third, vacume leaks. Fourth, replace the PCV valve. A great write up for that is under the FAQ. You should doo all of these things but only one may actually be causing the stumble in idle. For me it was the MAF that was really dirty.

Jon

For me changing the O2 sensor cured my idle problems.

Thank you guys, I'm on it. I was just hoping that the fact that it didn't idle rough in Neutral might be a help in narrowing down what it could be, but I guess that'd be too easy haha. Thanks again guys.