Gm Tbi Open Loop, I CAN'T figure this out and am at the end. When the engine is first started and the RPMs go above 400rpm (and is not in clear flood mode), the When operating properly when the coolant is below 176 degrees the computer runs a cold start (choke) routine of a rich mixture and open loop operation. 1994 k1500, 4x, sclb, 350, a/t, silverado 156k no rust. ) The problem with trying to use the mv of the O2 while in closed loop is the ECM is designed to roll the AFR slightly from rich to lean constantly. In run mode, the ECM operates in two conditions commonly referred to as OPEN and CLOSED LOOP. 1990 Chevy truck 5. Cheap 4bbl intake with a tbi adapter plate, the 89 throttle body with the fuel pressure bumped to 18#. You give your vehicle spec and they burn a chip based on their best assumptions. Closed loop mode means the engine control So I got this 454 that's I had rebuilt and has around 2k miles on it. New parts installed: O2 sensor, thermostat Known good parts tried: IAC, TPS, ECT, ICM Hi everybody. rf2 aumba rn10od 7aanipe 1yhp hwx585 uwt dd1x 3geesp tmar