1999 Ford Explorer 6 L 4.0 cyl

The car has 125k miles on it.
Check engine light came on, codes read that fuel mixture was lean. Another problem I'd been having was that upon starting, car would idle into a stall. So, had the idle control valve replaced, but apparently it wasn't the correct one. Engine cover had to be modified to have it fit. I had the vacuum tubes replaced, check engine light was still on. A mechanic put a rubber cap on the idle control valve, and it seemed to fix the problem temporarily. I drove for 1000 miles, no trouble. I started the car on a cold morning, and it was having idling troubles like before, I started driving, and the check engine light came back on. Do you think I need to get the proper idle control valve or could there be another problem for it? I ran some fuel injector cleaner through the system as well.
Have the codes read again to avoid a mix up......and its always best to go with OEM parts
If someone sells you something that is an emission part and has to modify the vehicle to get it to work, it is the wrong part. It could be allowing air to leak around tha base of the part.

Being way2old is why I need help from younger minds Thanks for the help. I bought an OEM part, gonna try that out and see what happens. Is the only way that I can reset the check engine light be through someone with a diagnostic reader?
That is the best way to have it reset. Some parts houses will read and erase the codes for you.