Currently chasing a gremlin that causes intermittent tachometer operation. In this interest, I grabbed a spare ECU out of a junkyard car. It was the same as mine, 2.3 dual plug. After the swap, the idle was very strange. surged between 450-950. almost had the 'cam' effect. very heavy fueling during the surges, little puffs of rich exhaust. drove fine after 2k rpm, but part throttle operation below that was also odd and had sputtering. The original ECU seems to be a C1A1. The new one is an 8CC. This is the 'catch code' as it seems it called. My question is, what is the difference in these ecu's? They came out of the same cars, at least the same year range and engine, yet seem to function differently. The casings even look different. EEC-IV geniuses, are you out there?