Code 26 (QDM #1) monitors three circuits, it says ECM does not see correct voltage on EGR Solenoid OR on EVAP solenoid OR on Air Pump Relay. Are they all installed, connections clean, fuses good and wiring intact. Code 28 (QDM #2) monitors two circuits says ECM does not see correct voltage on Fan Relays OR on A/C relay , check wires, connections, fuses, same as above. Your NO reading at 15 MPH was very close to failing with a 674 that indicates "possible" EGR problem . The code 28 will not effect emissions unless car is very hot (over 250* F) during test. High HC is usually a dirty/rich burn caused by what coco has mentioned. Also fouled plug, bad spark, HV wire shorting, O2's bad, worst cast low compression, top end problems, etc. Seafoam in intake may help clear fouled plug(s) or top end crud. What did you do/change in the 'Tune Up' that you mentioned in post #3. Also when tested, was the car hot enough for your non-heated O2's to be working correctly, keep it running while waiting. Do you have any mods ?
I'm Bob.. 1994 Z28, A4, Stall, CAI, Cam, RR's, 342 rear, LT's , CatBack, Tuned
Last edited by bobdec; 02-26-2013 at 09:22 AM.