Can a remote starter affect gas mileage.

Was it a dealer or mechanic who installed it or dude at the remote starter store. I would find out where they are referencing the tach signal for the remote starter unit. On the GM's I connect to a injector - signal wire which is OK most of the time. I'm thinking that they tried the same thing but something is not right and the module or wiring is shorting the signal wire causing the injector to spray fuel continuosly.

It was the auto electronics shop. They have a good rep but who knows. Thanks i will check that out.

Also if that is the problem you may want to check/change the oil there may have been unburnt fuel passing by the rings.