I replaced engine in 1989 740 GLE - B234F engine with used engine. My old engine acquired a bad bearing knock so I bought another engine from salvage yard. Replacement went fine but I now have a check engine light and get a 1-2-3 error code. I understand this to be Coolant temperature sensor. I replaced the sensor on the new motor with the one from my old motor since I had no problem with this before. I still get the 1-2-3 code. The syptoms are that it is hard to start... cold. Once it does start and I let it idle(roughly) for a minute or two, it then runs fine even though the check engine light never goes out. I can kill and restart the car fine as long as the engine is warm. But after it is off for several hours and allowed to cool off, the cold start problem is still there along with check engine light and 1-2-3 code. I see in the FAQ's that the ect is under the intake about the #3 cylinder but on my motor, it is actually near the #1 cylinder, the sensor to the gauge is near the #2 cylinder and there is a plug in the port near the #3. I know I am on the right sensor because I can unplug the one under the #2 cylinder the the gauge quits working. This is however the same configuration as the previous motor and I had no check engine light nor cold start problems. Any suggestions as to a fix? All I have checked is for broken/faulty wires between sensor and harness plug near firewall - no problems there. How can I besure the sensor itself is ok? If it is ok, where do I go from there? Nearest Volvo dealer is over 100 miles away and I can't find a mechanic close that is willing to tackle a Brick without me writing a blank check.