1997 Chevy S10 2wd 2.2l Recent head gasket job. 1. Runs rich at idle (stft-18.8. Ltft-7.4) Eventually throws rich code (p0172) Idle fluctuates when warm, mainly when coming to a stop. Drops down to about 400 rpm, lights dim, engine almost stalls then revs back up to about 1200rpm then...