I have a 1991 gmc 2500. It eats gas somethin awfull. I changed the spark plugs, and it passed smog, now it idles a little rough, and still eats gas. What do i do...
are you getting any service engine codes
Colder temps will cause an increase in fuel consumption, check the thermostat, make sure it is operating properly and not stuck open, make sure the air filter is clean, double check base engine timing, this is a OBD1 system so the ignition timing can be adjusted, then you need to have the codes checked for out of specs sensors.
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