Hi, all I did was change my valve cover gasket. Now I have code P0300 multiple misfire....how the hell does that happen? any help please!!

 

Now I got code p01136 and p01151 this is crazy over a stupid gasket!

 

How did it run after the gasket swap? must have been little rough, cause you pull the codes or no?

If nothing before the gasket change those codes all could be explained by wiring on the engine disturbed during the work, some either missed not re connected and or knocked loose so no longer making solid connections.

P0300 Random/Multiple Cylinder Misfire Detected
P1136 Fan Control Circuit Malfunction
P1151 Lack Of HO2S21 Switch - Sensor Indicates Lean

Say for example couple injectors not getting solid connection key on power and or PCM circuit feed, if has dead miss that could account for multiple cylinder misfire and resulting lean condition because of it.

Fan control, perhaps simply forgot to plug it back in? (does it have the factory injector blower on it?)

Regardless if it had no issues before changing the gasket then you need to double check your work. Make sure you plugged everything back in making solid connections doing so, connectors securely locked to each other.

Connectors tend to be weather proof however any unplugged during service work should be checked for signs of corrosion, something done about it if/when found.