Beware when buying a car maintained by a do it yourselfer!
We recently diagnosed an interesting AirCare failure on a 1993 BMW 320i that inspired me to reflect on the work that some do it yourselfers do. The vehicle failed for very high carbon monoxide and hydrocarbon emissions and while performing diagnosis and road testing I noted on our diagnostic computer that the engine’s coolant temperature was only reading 30 degrees Celsius with the engine hot. It should be at least 80 to 100 degrees!
The engine’s computer was getting the signal that the engine was cold and enrichening the fuel mixture and very likely causing the elevated emissions. Testing the coolant temp sensor and wiring was the next step. What I found here was amazing: the coolant temperature sensor was not connected and after an exhaustive search for the wiring connector I finally found it, buried under the intake manifold with another coolant temperature sensor connected to it sitting out exposed to the air! The sensor was reading the air temperature in the engine compartment. Why someone would go to such an effort to do something clearly so stupid is beyond me. Reconnecting the sensor correctly restored all concerns and the vehicle passed AirCare with great readings.
While there is nothing wrong with do it yourselfer work beware when you buy a car from such a person. Clearly this person had an idea of what they were doing but it made no sense and clearly showed that he had no understanding of what was required to keep a car running properly. This crazy repair not only created excessive pollution, it was also wasting gas in a big way.
If there is a lesson here to be learned, always ask who has maintained the car that you plan to buy: if the answer is “I did “or “my friend is a mechanic” be wary. You might just end up with this sort of horror story.