1989 300e cel come on when it is at operating temperature. it has a code for coolant temp sensor. i replaced all and tested for power to them. it still comes on. please help

also has a code for no power to the altitude gas thing attached to the throttle body

You might try a new radiator cap as they tend to go bad. You could have an internal engine problem as well causing this. You can also get some coolant additive that will allow the engine to run cooler, it works pretty well. You also might have a water pump problem.

it does not over heat. tested sensor to fan and fan works. already replaced the thermostat, radiator cap, fixed all vac leaks, tested all relays, new overload protection relay, new distributor and rotor, tested plug wires, new plugs, new alternator, new battery, tested idol air control valve, new 02 sensor, and the car runs good. oil stays clean and it burns none.

coolant stays clean-no rust

I can feel the flow in the hoses

no leaks of coolant

Replace the EGR (Exhaust Gas Recirculation) valve. Cost about $350 (new parts and labor included) on independent european mechanic shop.

Try to Unplug and Plug the Mass Airflow Sensor.

Make sure the electrical connections to the temperature sensors are clean. I would not go wild unplugging things that are completely unrelated as Honesto suggests, that is a recipe for creating more problems.

they are all clean and have power. there is some sort of flow meter in the battery compartment that coolant is routed through. it looks very old. do you know what this is. it is round and has an electric plug. nothing happens when I unplug it. no change

ok-the round thing is the Auxiliary Engine Water Pump. assuming it has nothing to do with it. the maf cuts the car off when unplugged. I assume another code for the egr would appear if it were the problem I am not ready to replace a part that expensive with no reason. could that even be related to the code in any way?

maybe my codes are wrong. or guide anyway. in pin 6 I get 3 flashes, then 8, then 9 before it starts all over

this is 1989 I thought 3 was coolant sensor, 8 is no current to altitude control deal, and 9 I am not sure. I may have the 1990 300e code guide. anybody know? is it different?