I get a rich code on bank 2 and an engine miss at 4200 rpm, but the code comes on for a few days then goes back off. I understand some of the issues that cause this code but why is the code not staying on? I was hoping I could nail it down before I go buy o2 sensors, MAF sensors, or start replacing injectors. I am running sea foam every 3 or 4 tanks to help keep the injectors clean. The truck is a 2004 fx4. Plugs and coils are new and I run the stock air filter. I also just recently cleaned my MAF sensor. Any ideas guys before I shell out 150 to let the stealership diagnose it?

 

Run an OBD II scan, write down the codes and document. Navigate the pages offered by the scanner and open them up. Document the readings it gives, all of them. Look 1st at vacuum hoses and make sure they are not kinked, cracked or plugged. If old replace with new and clamp them so as not to leak air. You are looking for a very small vacuum leak. A propane torch not lite but slightly turned on held close to a leak will raise the engine idle rpms, a sure leak. Your codes and tables can point you in the direction of the MALF, probably in the evap sensor, purge valve etc. Your obi scanner can eliminate things like fuel system, o2 sensors, catz, and show you what test ok, not testing, incomplete etc. Good luck