My 2004 Pontiac Grand Am with a 3400 engine and 205,000 still gets 27 mpg on the highway but suddenly only getting 13 in the city. The city mileage was 23-24 until the last couple of months. Changed oil, replaced air filter, not surer what to do next.
No Check Engine Light?
Tester
@eisjeff
Is the engine reaching operating temperature in a timely manner?
If not, might be time for a thermostat
Also, when was the last tuneup?
Does it still start easily?
Is it running well?
One additional question; have you had this car for a long time or is it new to you, and do you live in an area where the temperature has taken a dive these past few months?
Okay, that’s two. But they ARE related! {
Are you sure the transmission is shifting through ALL the gears?
One of the things I can think of which would suddenly change fuel economy is a leaking fuel pressure regulator. Do you have any symptoms like hard starting after warmed up? Poor idle? To check regulator remove vacuum line going to it and check for the presence of fuel.