check engine light goes on. codes read and say: P0118 coolant temp sensor defective,P0303 cyl 3 misfire detected spark plug worn. the car has had many electrical problems generally and has cost me a fortune. two months ago entire ECU was replaced, just to get car to pass inspection. this time, after codes read,CEL light does not come on again despite driving another 150 miles. the car will go into the shop (again)butany advice appreciated. last addition:a few weeks ago, there wasa spell of bad starts (engine would churn but not catch easily).

 

you need a new coolant temp sensor and either a new spark plug or coilpack. try switching the coilpack and if the misfire follows it, then its the coilpack. if it stays on that cylinder, its the spark plug

 

thank you.

 

a follow-up: mechanic not impressed enough to intervene! says that at 34,000 miles (it's a 2002 A4) and with lights staying off, i should try a new tank of gas first. doesn't believe the coolant temp sensor or plugs should be out at this mileage, and that maybe there was a stray misfire. if lights go on again, i'm to go in.

 

P0118 = Engine Coolant Temp Sensor ( ECT ) fault is high input, possible cause is coolant thermostat, wiring open circuit/short to positive, defective ground wire, ECT sensor.

Ive seen these things go with much less miles on the clock and as for the spark plug or coil pack ( it could be a boggy code one off because the ECT could cause that ) but personally I agree with chaos,
you could clear the code and see if it comes back failing that do as chaos says