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- United Kingdom
Just noticed you're still dealing with the drop in revs.I searched online for the rough idle problem and a lot of Rangers and F150's and Expeditions seem to be suffering from rough idles.
"Solutions" range from replacing the IAC, throttle bodie to vaccuum leaks.
No one has posted an actual solution, so until then, I'll see what I can do with the sensors in the engine.
Hopefully it's a simple solution, like filling up the AC to increase the pressure.
While I can't claim there's any similarity between your Ranger and my MX-5, my Mazda nevertheless had a very similar-sounding issue when I picked it up, and actually stalled a couple of times when pulling up to junctions.
In that, it was caused by the idle screw on the throttle body. It's a mechanical setting for the idle when the ECU isn't controlling it. If the screw is set too low, then whenever the ECU isn't in control of the idle, the revs drop. Then, when the ECU kicks in again, the revs rise - which could be why yours is returning to 800rpm after a few seconds at 500rpm.
On the Mazda, you fix it by shorting out the ECU-controlled idle with a paperclip, which drops the idle, then turn the screw until the engine is at the right RPM. You may find it's a similar fix on the Ranger. It's also a free fix, so it's a good place to start before investigating more expensive fixes.