Hi everyone. I am trying to diagnose a problem with my girlfriends 2005 Civic EX, 71000 mi.

A few months ago her car slowly started to lose power and then started to misfire then throwing a check engine light. Hooked up the scanner and got codes for cylinder misfire on each cylinder. Went to autozone, got some NGK spark plugs. Car drove fine after that. Then it started misfiring again and gas mileage went way down. I later found out autozone gave me the wrong plugs and so I went to honda to get the correct OEM plugs and everything ran fine for a few weeks. It hasnt been misfiring since, but the gas mileage is still pretty low and every now and then, she will have some problems starting it (mostly in hot weather after short driving trips). The car will turn over just fine, it just wont fire up right away. eventually after continued cranking, she would be able to start it.

Could the initial set of wrong plugs have damaged any sensors or probably the cat?

I got some OBDII scan data if anyone can help me understand the data.

This is when the car is at idle and warmed up
Long term fuel trim: -3.9%
Short term fuel trim: 7.0%
O2 sensor volts: 0.7v
Intake press: 3.8psi
Timing Advance: 7.5deg
AFR: 14.6
Coolant temp: 204.8 deg F

This is when the car is cruising at 65
Long term fuel trim: -3.1%
Short term fuel trim: 2.3%
O2 sensor volts: 0.7v
Intake press: 7.7psi
Timing Advance: 31.5deg
AFR: 14.5
Coolant temp: 186.8 deg F

Thanks a bunch for any input guys!

 

- Another Very Old Post Revived -

Turned out the valves were not seated properly. Head needed to be rebuilt.