so my ford ranger has a low rpm and miss at idle. i can hear a clicking noise under the hood its the alternator disengaging and reengaging. intermittently stalls out. at times rams will get as low as 250 once warmed up stays around 500 but still missing. any advice on where to start with this issue?

 

Welcome to FTE.

I see you don't have any replies yet, so I'll see if I can get things started.

If you like doing your own diagnostics & wrench turning repairs, use, borrow, or come by the inexpensive but powerful ELM scan tool & running FORScan diagnostic software on the viewing device of your choice as discussed here https://www.ford-trucks.com/forums/1...-scantool.html, have it query/scan all of the vehicle computer/controllers for trouble code clues & post All code Numbers, as they can help focus a trouble shoot in case you have more than one problem.

The alternator doesn't cycle on & off, but the AC compressor clutch does, as system pressure rises & falls, so that sounds like the under hood clicking your hearing.

The engine IAC = Idle Air Control sounds like it belongs on your suspect list. It's located at the end of the intake air tube, where it attaches to the throttle body. It's responsible for controlling engine idle speed as various loads come & go, like the AC compressor cycling on & off, the power steering pump adding load as we turn the steering wheel, or when we put the auto tranny in gear, turn on heavy electrical loads that the alternator has to take care of, so it loads the engine, the engine cooling fan, etc , so it sounds like the IAC is acting out if it's not idling the engine rpm up as loads change.
It's a common problem part. It may, or may not set a trouble code to turn on the dash CEL.

A operational test for a faulty IAC is with the engine idling with the climate control turned to OFF, disconnect the IAC electrical connector & if it's working the engine idle speed should drop, the engine might run rough or stall. If nothing happens it's not working.

If you come to suspect yours, you might try removing & cleaning it internally with a plastic safe spray cleaner, like CRC or Valvolene MAF sensor spray cleaner & maybe some good quality cotton swabs, but be carful not to leave any fibers behind.
Keep the electrical connector end elevated, so cleaner or debris don't enter the solenoid winding end of things & corrupt the windings insulation, or bind up the solenoid movement end of the idle air bypass solenoid shaft.

This cleaning didn't last for me & is probably why Ford recommends replacement rather than cleaning when they begin acting out, but cleaning was a good trouble shooting step for
me. My idle woes stopped for a couple of months after cleaning, but suddenly returned, so that's when I replaced mine.

If you come to suspect yours is kaput, Motorcraft, or BWD brands are recommended for quality, by members that have replaced theirs. Mine is BWD & is about 10 years old now & doing fine.
With a Advance Auto order online promo discount code that you can find here https://www.retailmenot.com/view/advanceautoparts.com & with pick up in store to save shipping, it was Way less expensive than others.

Some beginning trouble shooting thoughts for consideration, let us know what you find.

 

replaced the ica and is purring like brand new thank you!!!

 

OK, good find, fix, feedback & to hear all now seems well & the low rough idle, or stall is history with the IAC replacement.
Would be interesting to know what brand IAC you opted for & how long it lasts, so let us know how it goes with it over time.