1990 Ford Mustang check engine light

Code 11 is just a pass code which indicates that there are no recorded service codes in that portion of the test and that the system passes that portion of the test.

Code 13 indicates engine could not be controlled within lower RPM range during self-test. Possible causes for this code include vacuum leaks, incorrect idle setting, throttle plates open, stuck throttle linkage.

Code 19 indicates that with ISC off, engine RPM dropped below self-test limit (approx. 600 RPM). Possible causes are incorrect idle, throttle body/air inlet contamination and/or engine below normal operating temperature.

Code 34 indicates that the EGR valve and/or EVP is not fully seated in the closed position. Most likely culprit is faulty EGR valve.