engine code reads coolant temp senser, but replaced 3 times, code still pops up. on 1990 Mazda B2200

the truck is really hard to start up in the morining mostly have to push the gas pedle all the way to the floor to get it started. while started the rmp idles to 2500 rpm.

Asked by for the 1990 Mazda B2200
The sensors may have all been fine. You need to check the wiring and the ECU (computer) We have had several Mazda ECUs repaired.