I have a 91 525i chassis that has had an S52 motor installed and is using a 413 ECM. I recently rebuilt the motor because of a leaking headgasket, worn rings and bearings. The only difference in the drivability is that the idle is now running around 1000-1100 (and lots more power). Everything has proceded smoothly except for the nagging code that pops up. If the engine is idling for mor than about a minute the CEL illuminates with the 1226 code (Throttle Position Sensor failure) showing on the stomp test and from the Peake R5 reader. If I add a few revs while idling (at a stop light) the CEL stays dark. The CEP stays dark if I restart the motor. I have tested the TPS (was within spec), but replaced it anyway since it was 22 years old just to remove doubt. What's next to check?