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The EEC 4 code list is as follows. 12
Idle Speed Control motor or Air Bypass not controlling idle properly (generally idle too low) 35
EVP - (R) Engine
RPM's too low to test EGR system
EVR - (O, R, M) EVP sensor signal is/was high
PFE - (O, R, M) PFE sensor signal is/was high 58
Idle Tracking Switch (ITS) signal problem
For the 9521
Temperature (ECT) sensor out of range 72
(R) No MAP or MAF change in "goose" test - retest, check for frequency or voltage change32
EVP - (R) EGR not responding properly during test63
Throttle Position Sensor (TPS) signal too low 41
(R) System lean
(M) System was lean for 15 seconds or more (no HO2S switching)
Best thing to do in my opinion, is clear all the codes, Crank the engine, and see if any come back, whichever code comes back first. is going to be the primary code and it should be addressed first.