94 X giving CEL code #538

4.0l engine supposed to be professionaly rebuilt prior to my owning it. Have eliminated codes for fuel pump circuit and am stumped on this one. Thinking
it might be burnt valves, vacuum leak in high/low intake,bad O2 sensor in bank 1. any ideas are appreciated.
Thanks

Welcome to this forum! I wrote a thread about the 2, and 3 digit codes in the EEC IV section. Here is a link to that thread: http://www.explorerforum.com/forums/showthread.php?t=160035. Here is what code # 538 means:
538
Insufficient RPM Change During KOER Dynamic Response Test
R

538
Invalid Cylinder Balance Test Due To Throttle Movement During Test
R

538
Invalid Cylinder Balance Test Due To Cylinder Identification Sensor Circuit Failure
R

C—Continuous memory code.
O—Key On, engine Off self test code.
R—Engine running self test code.

apon further inspection found "caked-on crud" from throttle plate to back of top intake down into low intake. Cleaning that out and openning throttle plate as it sticks closed now. See what that does. Keep ya' posted