My 91 Honda Accord EX coupe (automatic) with 170K has begun to run rough between 1500-2000 RPM under load.

I first thought it was a bad cap & rotor so I gave it a full tune up (new NGK plugs, rotor, cap, fuel & air filter, oil change and checked timing), problem continued.

I thought maybe it was the o2 sensor so I replaced it, problem continued.

I checked the ECU for codes and 12 was displayed although check engine light is not illuminated.

I checked the EGR and it seems to be operating correctly but I still replaced, no change. (Note: I used salvage part, looked new)

I then changed the purge cut off solenoid, EGR control solenoid and constant vacuum control (CVC) valve. NO CHANGE! (Note: same as above)

PLEASE HELP!

 

Plugged EGR ports in the intake manifold can cause a partial load misfire on that vehicle. Won't cause a code 12 though.

 

I cleaned the ports where the EGR mounts by spraying carb cleaner into them and blowing them out. I'll try it again and see what happens. Thanks!

 

OK I cleaned the ports, same deal. Just for ***** and gigles I replaced the MAP sensor and canistor but no change.

The last thing I did was fill up with 93 octane and add a penzoil injector concentrate cleaner on top of an already added lucas injector cleaner and it seems to have diminish. We'll see how it resonds as we consume the tank.

Bizare ain't it! I'm trully stumped with this problem! Any suggestions would be appreciated!