Idles @ 2100 RPM
 

I just replaced an oxygen sensor since that was the code that the guy at Advance Auto said it needed. It still idles high and sometimes it barely idles. The CEL is off but not sure what to look for next. Could it be the throttle position sensor?

Try unplugging you iac valve.

I unplugged it and it wouldn't idle at all. Not sure what this means though? Around the same time this happened the air conditioning started blowing through the defrost ducts only. Don't know if it may be related to just coincidence.

The Ford Ranger by design idles high on cold and warm start for a certain period of time. During the winter months my Ranger idles at about 2200 RPMs on cold start and then holds at about 1500 RPMs after 5-6 seconds. And if you have the defroster on, the A/C compressor runs by design and usually causes the engine to idle higher. And if that doesn't help, check for a vacuum leak or any signs of MAF sensor malfunction, because if it is idling high it could be not getting proper airflow readings, causing it to run rich and idle high. I don't know exactly

Yes I would say it is mine did the same thing I have a 94 4.0 5spd and when at idle it would drop to under 500 rpms and almost stall then would spike to 1200 rpms but I haven't seen 2100 rpms I would try the throttle position sensor after I changed mine it ran fine it still idle'ed funny but much much betteri still have to replace the MAF sensor. Sensors are junk on these fords my check engin was on for 3 things all sensors haha

i replaced my iac and the tps and it fixed the problem...mine was idling at 2500 and would nvr go below

Ya i was going to say IAC for sure. If u unplugged it and nothing changed it wasnt doing its job.

Before you start throwing parts at it check for vac leaks first!