About 3 years ago I got a check engine light and 2 DTC's off the OBD2. It was throwing a misfire in cylinder 3 and the random multiple misfire. I stored the car with my parents while I was stationed overseas for 2 and a half years. I recently returned to a car that was still running decently, but I wanted to get rid of that pesky light. I replaced the spark plugs. The old ones were very sooty. Then replaced the coil packs. Nothing fixed. My parents admitted to running crappy gas through it (87 i think) so I drained it and filled up with 93. I've run about 5 full tanks through and even tried some Seafoam. Still nothing. Last week I tore the valve cover off for painting and decided to go ahead and do an adjustment. An exhaust valve in cylinder 3 had no gap whatsoever and one of the intake valves was pretty loose so I adjusted them, bolted it back up and reset the ECU to see what I got. Hooked up the scanner and the only code I have now is P1399 with a steady "CEL". The "emission status" on the scanner was in the yellow (not bad, but not great) and the little indicators for the O2 sensors, catalytic converter and EVAP system were flashing. I'm going to go buy a compression tester later this week.

If the compression test goes well, what should my next step be? Do you think it's anything to do with the CAT or o2 sensors? Or should I be looking more at injectors? I really don't think I have a valve issue but I won't be certain until the compression test is done.

'02 Silverstone Invidia N1, K&N Typhoon Intake

 

Have a look here
https://www.s2ki.com/s2000/topic/659930-misfire-thread/

 

Zero gap on the exhaust valve clearance can burn a valve.

Do a leakdown test, compression test does not usually pick this up.

Think of a leakdown test as a high precision compression test. It will show things that a compression test simply can not show.

 

Check for cracked retainers while you're in there.

 

Thanks guys. I'm going to do the leak down test tomorrow and I'll let you know what happens.

'02 Silverstone Invidia N1, K&N Typhoon Intake