I would check for vacuum leak. Just check all hoses for any cracks or holes. I had a pretty small hole in one of hoses on explorer it ran terrible. I bought replacement hose n clamps for couple bucks. ALSO CHECK EGR VALVE
Probably an alternator.
Timing belt could be bad and could have jumped a tooth or you need a toon up.
Dirty injectors.
Need a little more info. What Model and year of the vehicle?
idle control valve faulty or needs cleaning
Carb.? Float sticking? Rebuild or replace
replace the alternator
ran in to same problem with 93 escort. went to ford escort owners association (feoa.net). my problem turned out to be a vacuum leak. the forums will help narrow down problem. there is also a way to check and find out error codes on the site.
lol that's what its suppossed to do... if when idling low it stalls or is really roush then you might have a real problem.
id change the coolant temp sensor
Mine did this and I found out it was the timing belt that needed to be changed.
it could be the tps sensor, map sensor, idle air control vavle, in jection problem, or something simple as a fuel fiter dirty, check the fuel pressure with a fuel pressure guage that you can pick up at any auto parts store