I just had a tune up done on my '96 explorer about 6 months ago. now my truck has a rough idle, sometimes...this is the hard part, it doesnt always have one. of course when I take it the mechanic to get it serviced, it runs perfectly smooth.

sometimes if i'm sitting at a light or driving at low speeds (like through a school zone at 20 mph or lower) my engine's rpms will drop to around 500 or lower and nearly stall. if i shift it to neutral and give it some gas, it'll sometimes idle smoothly at around 1000 rpms.

and on wednesday, i ran the a/c for a short drive across town and the truck ran smoothly. i parked the truck for about an hour, when I tried to start it again, it barely started, it would only idle at just under 500 rpms and it kept stalling the whole way home at every red light or traffic jam. i had to keep restarting it or shifting it into neutral and rev the engine to keep it running.
it doesnt do this all the time, maybe once every 2 weeks. i'm wondering if my valves need to be looked at, maybe they're sticking or wore out?? my explorer just turned 106k miles yesterday.

i had the oil changed recently and the guy there said i needed my gearbox done, he said usually at around 100k the gearbox is shot, could that be the culprit? it'll only cost me around 40 bucks to have that done. but i dont want to waste 40 bucks when that isnt the problem.

any help or suggestions will be appreciated.

 

sounds like you have a bad Idle Air Control Valve(IAC).
Read the "sticky" on IAC

p.s.
you said you did a tune-up @6 months ago........what all did you replace?
Also what engine are we talking about, its it 2wd, 4wd is it auto or 5-speed?

These answers will help you get better responses......

p.s.s.

I seriously doubt that your gear box is the culprit

 

I have a 2WD 6cyl automatic

I got the spark plugs and wires replaced, shocks & struts replaced, oil, transmission, and coolant fluids changed. they said they checked the valves, hoses and wiring systems for cracks or holes or any other problems. and they said everything was fine except for number 4 cylinder's spark plug wire was showing wear it looked like it was rubbing on the exhaust manifold. they fixed that.
and they checked the timing on the engine. they also checked my brakes and alignment and rotated and balanced the tires.
Thanks for the info on the IAC valve.