1991 RRC 215k miles 3.9 engine running the 14CUX. Engine will fire right up and idle no issues steady as a rock, rev to 5k no problems no hesitation. When in gear Hi or low it does not matter will not get over 1300 rpm. it will then drop to 800 rpms and then pick up to backto about 1300 and will do this. Let off the throttle to 1200 and it will drive. Bury the the throttle and it just dies.

Have cleaned the maf, no improvement. Have swapped the maf still the same any pointers on where to go from here?

Thank you

 

Any fault codes from the little code reader?