have got these codes along with a very high idle, have changed the oxygen sensors, idle air control valve, throttle postion switch and coolant temp sensor. also changed the pcv valve along with the attached hose. have found no vaccum leaks. only parts left to change as far as i know are the mass air flow sensor, map sensor & the computer prossesor itself. truck has 103k on it, starts but doesnt want to stay running until warm , then when warmed up wants to rev to 2,500 when clutch is pushed to shift or come to a stop, when speed gets below 10 mph when coming to a stop will slow to 1,500 rpm. my "code book" doesnt give me a clue as to what direction to go next, im running out of peices to change but also running out of cash too. any ideas? im officially stumped.

538 just means that you didn't goose the throttle during the KOER test. So that isn't anything to worry about.

The other 2 codes are for lean conditions. Recheck for vacuum leaks - they can cause both a lean condition and a high idle. Don't overlook the pcv hoses. Gaskets that seal the intake manifold to the cylinder heads are also known leakers.

finnally got it figured out, turned out to be a failed gasket. the fuel rail which is sandwiched between the upper and lower intake had the gasket between it and the lower intake pulling into the intake ports at the front and rear. idles fine now, i ran a compression check before i started to see if i had a problem there, its looking good for 104k with 185 on 4 cyl and 175 on the other 2. glad i didnt need to pull the heads. i pulled the lower intake just because i was that close and had the gasket, no issues there, looked good and clean. had the camera but ran out of battery before i got it compltely tore down. had the hood off, that made things easier but who knew a ranger hood could weigh so much.
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