MY 1990 740 B230F engine runs erratic at idle after about 15 minutes of opertaion. I removed the cylinder head because the plug threads needed to be chased. Installed new plugs, new head gasket, new intake gasket, measured head for warpage and found none. Installed and problem of running rough at idle began to occur(this was not a problem before I pulled the head). Subsequently I have replaced distributor cap rotor, plug wires, coil, timing belt, fuel filter, fuel pump check valeve, fuel pressure regulator, all to no avail. Problem still exists. Continued trouble shooting ran one can of sea foam through gas tank. Compression checked good, air filter good. Listened to injectors with stethescope while running and could hear clicking indicating proper operation. Ohm checked injectors 16.0 each. All hoses and connectors good. Found electronic control unit temp sensor to be reading high ohms throughout temperature range. Replaced temp sensor. Air mass sensor reads 2.8 ohms between terminals 2 and 3. Fault codes, test mode 1, table 1, 2-3-2, fuel trim(lambda control). Could not find sensor only line leading from exhaust across back of engine to bellows under intake manifold which led to egr system controller. 1-2-3 signal missing to/from coolant temp sensor. Table 2, 2-2-4, engine coolant temp sensor signal absent or faulty. Test mode 2, 3-3-4, throttle position switch operates properly. 1-4-1, rpm sensor good. 3-3-2, tps okay in idle position(when throttle is moved). 1-1-4, A/C control on/off good. Any suggestions from someone to possibly pinpoint problem.