A few days ago, the Check Engine light displayed on my 91 Volvo 240 B230F. I pulled the engine codes, and it blinks "1-2-3". The FAQ says this is due to a "signal missing to/from cooland temp. sensor". I drove around another day or two, and suddenly the car is extremely hard to start when the engine is cold. Again, the FAQ says this is a symptom of a wiring fault to or in the ECT sensor.

I searched online for several sources, which display the ECT or water temp sensor with a wide plastic connector (Bosch #0280130032). This sensor fits under intake manifold port #3.

I went to my local Volvo dealership, and they sold me the "Temp. Sender" (Volvo #460191-0), a smaller sensor with a slender blade-type connector. This sensor fits underneath intake manifold intake port #2.

Which one do I need? What does the Temp Sender do? Should I replace it too, or go back for the right part?

BACKGROUND: Six weeks go, my coolant thermostat cracked, the engine overheated and blew the cylinder head gasket. I got the cylinder head resurfaced at a machine shop, cleaned both these sensors with a wire brush, and reinstalled them in the cylinder head. It ran OK, a bit hard to start when cold, but recently began to lope/idle erratically. After the check engine light came on, it takes several tries to start in the morning. Could it be something other than the sensors causing this problem?

[[ southern fried volvo '91 240 135k mi ]]