Thread: Rough idle except for neutral

My car is starting to idle roughly in every gear except neutral. Any thoughts? Is it really a rough idle is something wrong with the tranny?

Is your check engine light on? When was the last time you did a tune-up (plugs,wires, air and fuel filter, pcv valve)?

Could be a vacuum leak. Check all your hoses and connections with carb cleaner. Also check around the UIM as they are known to crack.

Have you cleaned the MAF?

And no, I don't think it's a tranny issue. When my car had a massive vac. leak it would run great in Park and Neutral as well, but as soon as you put a load on it (i.e.- putting it in gear) the idle would suck and I would almost have to 2-foot it to keep it running.

Jay

Originally Posted by FordMan77

Is your check engine light on? When was the last time you did a tune-up (plugs,wires, air and fuel filter, pcv valve)?

Could be a vacuum leak. Check all your hoses and connections with carb cleaner. Also check around the UIM as they are known to crack.

Have you cleaned the MAF?

And no, I don't think it's a tranny issue. When my car had a massive vac. leak it would run great in Park and Neutral as well, but as soon as you put a load on it (i.e.- putting it in gear) the idle would suck and I would almost have to 2-foot it to keep it running.

Jay

The check engine light is off, and I haven't changed my wires or spark plugs in 2 years/20,000 miles or so, but I recently changed the fuel and air filter. I checked the PCV valve and it was fine. I did not clean the MAF though. Do I just spray it with carb cleaner? What's a UIM? I also wanted to mention that it idles roughly in Park too. Thanks for your help.

No, you want to clean the MAF with MAF cleaning spray. It's sold at parts stores and is specifically designed for MAF's. Carb cleaner will kill a MAF. While it is running in Park, try disconnecting the MAF and see if anything changes. Don't drive it llike this, just test it. Always reconnect it before driving.

The UIM is the Upper Intake Manifold. They have been known to crack and cause vac. leaks as well as coolant leaks, as there is coolant running through it around where the throttle body attaches.

Still give a close check for vac. leaks. I forgot to mention that after I replaced my UIM I still had an idle issue, and it was the MAP sensor that sits on top of the PCV valve. Mine had separated during removal of the UIM and was causing a strange idle. It looked like it was still all there and even stayed in the clips, but upon closer inspection I could tell the body had separated. Replaced that and all was well.

I also sprayed carb cleaner around the entire sealing surface of the UIM and all injectors where they meet the lower intake manifold to be sure mine wasn't leaking after the replacement, as with the old one I had a leak around #1 cylinder (front left corner).

Jay