Hi guys and gals! I've been trying to get my '95 GT back to running like a proper car, and now I'm deep into some ECC diagnosis. Can anybody help me with the codes below, specifically the 511, 212, and 412 ones? Okay, so here's what I did last night: Reset the codes with the diag tool. Drove the car until it was normal running temp. Ran a KOEO test. Got 511 & 565 operational codes, and 172 & 212 continuous codes. Ran a KOER test and got 172 & 136 running codes. Ran a KOER test again (because I didn't RTFM), this time got a 412 running code and that's it. Ran the cylinder balance test. It shows cylinders 2, 3, 5, 6, 7, & 8 all throwing codes. Good thing 1 and 4 are still okay, huh? Ha! 511 - This car was "tuned" by a previous owner. Would that cause a 511? 212 - Somewhere along the way this car received a billet Accel distributor and coil. Just giving full disclosure to help the diagnostic process. Should I be chasing a wiring short? 412 - The IAB is new and not a lick of carbon on it. I set the idle routine Friday with a hard idle setting of ~700pm. Just above surging. The car sometimes idles at 900rpm and drives great, other times it'll idle at like 1500rpm, jump to 2500rpm in between gears, and then almost fall on its face at 600rpm. Do I need to call a priest? Bonus points! Some coolant leaked onto my foot as I was driving. Heater core or head gasket?