Background: Previous owner killed engine in 2004 driving 13 miles without coolant. At that time, I paid $500 for 93 940 with 126k miles. Recently installed P&P engine after car sat in driveway during interum. Engine started after last wire harness connection plugged in and runs. But big jump in idle speed with TPS click. RPM jump is temp dependent: with cold engine from 750 to 1350rpm, half warmed from 750 to 1750 and with thermostat-open-hot engine from 750 to 2250rpm.

There are no trouble codes!! Seems IAC getting signal from ECU to pass more air dependent on engine temp with click of TPS.


Installed new, from dealer, Regina ECU temp sensor before installing original regina intake manifold with related hardware swapped for bosch that came on replacement engine. Thought problem from using wrong temp sensor but this weekend checked resistance readings, all are per graph in Green Book: as engine temp increases, resistance decreases to 223 ohms with open thermostat. Same resistance for both rex and regina sides of sensor.

TPS clicks with minimum rotation of throttle shaft. Have even plugged spare VDO (regina) TPS into harness so I could rotate throttle plate independent of click and that's only way I've found to have engine rpm increase slowly with out the jump. If you click spare TPS without it installed on throttle shaft you get same jump in rpm. Air to increase rpm only coming through IAC.

IAC is clean. IAC terminal voltages and resistances per Green Book and 300ms signal frequency seems to be consistant regardless of engine rpm: faint hum with ignition on and it gets louder with engine idling but no change in pitch with higher engine rpm. Suspect IAC changes ampitude but not frequency as air intake to increase rpm coming through IAC. With thumb over IAC inlet hose, engine idles smoothly at 200 rpm and acts like it could run that slow all day long!

Have replaced MAP and air inlet temp sensors with no change.

Have thought that problem from ECU but have accumulated 4 Regina ECU's from P&P with no change: all have same rpm jump when TPS clicks. Is it possible that 4 ecus are bad? Have not found ECU with paper label that indicates it was reprogrammed. Can one Regina ECU be reprogrammed who does it and what does it cost?

Jump in rpm feathered with tranny or A/c engaged. Change in rpm most noticable when using cruise control: car lurches when engines goes from 2250 rpm to engine braking at 750 with no change in throttle position.


Would appreciate any ideas to pursue that will cure this problem. Have driven Bosch equipped 240s since 1981 and have not had any problems. Recently sold 84 with almost 400k and car just nicely broke in.

Steve L in Charlotte.