1998 ford mustang 3.8 running lean rough idle and it cuts off. had tune up changed battery had it checked by 4 different mechanics they don't know what it is. help they say there are no leaks maf sensor is clean, alternator is good car is not over heating, fuel filter is not clogged. what else could it be?

SOURCE: 97 Ford Ranger 4.0L V6 Idles rough only when cold

Orand

Ther is a air Idle control valve located on the side of the throttle body. unplug it remove it spray it and clean it with carb cleaner replace it plug it back in and you will be a Happy person again.

Lugnut61

SOURCE: runs rough, black smoke, computer bank 1 burning too lean

Sounds like bad injectors, bad O2 sensors, and or too much fuel psi. Check the fuel psi against what the service manual says. If the fuel psi is too high, your regulator is bad. If the fuel psi checks out ok, you likely have a bad O2 or bad fuel injector(s).

SOURCE: ford 4.6 code po174 bank 2 too lean

O2 sensor faulty.

SOURCE: Very rough or low idle on braking, and standing at

check timing, Carboned intake manifold orintake manifold runner screws could have fallen out.

SOURCE: 04 mazda 6 lean condition

sounds like you have a vacuum leak. It is sucking in extra air from somewhere. possibly the intake manifold gaskets. The extra air coming in fools the computer / o2 sensors to believe it has a lean mixture then it will try to compensate for the lean mixture and add more fuel.