Hey guys. So, I've got a 2001 S2 ER34 Skyline, It's N/A. I bought the car and drove it around for about two months with no issues at all, then I started to get the check engine light come on, the car would lose all power and run on probably 4-5 cylinders, As usual, you could turn the car off and on and the check engine light would go away, but would then come on a day later or 5 mins later, completely random.
After reading up on this being a usual problem, I took all the throttle body off and found there was cheap ebay coilpacks in there. I removed them and chucked in a mates Stagea coilpacks, OEM ones. Put it all back together and drove it around for a day with the check engine light NOT coming on. Next day, boom.. check engine light. BUT, It wasn't losing any power/ running rough. Did the same thing, turn the car off and on and the light went away. It got more consistent. So I took the coilpacks out, took the plugs out, cleaned the plugs and checked the power going into the coilpack plugs, All 12volts. I checked they were all sparking consistently and the same. All good. I chucked everything back on and everytime I start the car, the check engine light will stay on, It drives fine, no misfire, no rough running.
Today I took it into a local auto elec and had a diagnostics run on it, Code 21. He cleared it, started the car up again and boom, code is back. Car is still running fine..
Does anyone have any idea as to what it could be... I'm stumped atm.