2001 Ranger low idle

My 2001 Ford Ranger 4.0 idles low and shuts off. The check engine light eventually comes on when it gets worse. From time to time the idle speed goes back to normal and everything is OK. If stays that way long enough the check engine light goes out. I can still drive it during low idle but it is a pain because it shuts off frequently when you come to a stop.
I took it to a auto repair shop but they could not get their diagnostic checker to work. We were not able to retrieve a code.

Any common things I could replace or check before taking to the dealership?

check spark plugs, wires, air and fuel filters

check spark plugs, wires, air and fuel filters

It has 38,000
I have replaced the air filter and cleaned the throat plate. It seems ambient temperature may cause it to be intermitten. Howver with cold weather it appears to be rather constant. I check the plugs and the wires and replace the fuel filter. We'll see if it makes any difference. That's for the info.

My 2001, 4.0 had the exact same problem so i took it to the dealership b/c it was still under ext. wrty., and they said it was a bad sensor that was located underneath the glove compartment next to the pass. door. hope this helps.

try reseting youre computer before you buy anything or pay for any kind of diagnostic.you can:

1) disconnect the negative cable on youre battery for 15 minutes

2) unhook the proper fuses (this will save youre radio presets and other stuff like that.)

my 2001 ranger just started with the low idle problem. did the bad sensor under the glovebox solve this problem.