My gas mileage has gotten worse!! I have recently replaced both 02 sensors, plugs & wires. I had been averaging about 23 mpg at the time. After the change it went up slightly and one week even hit 29 mpg. The past month or so it has been as little as 14 mpg and this week was 19.86 mpg and each week in between the 14 and the 19.86 it has been in the 18 & 19 range. What gives??? Is there anything else that I need to look at? My driving style has not changed in the least bit- still the same distances, speeds, etc. I have found I get better gas mileage when I don't use my cruise control.

Please help!!! All advice appreciated.

Air Filter? Clean the MAF? Are you in a cold state and just letting it idle for long periods(figure you'd probably already cover that, but doesn't hurt to ask)? Vacuum leak?

Go a little further.... Bad injector driver hanging an injector open?

If an injector was hanging open, wouldn't it be even worse than 14? :?

Have you checked the Air Filter?

You did use an AC Delco O2'*?

I don't think they were AC Delco'*. They were a gift from a guy we know and he got me what he said would work the best for my car. He also got me the plugs/wires at the same time.

I will have to have Jeff read this thread and check the other things mentioned because this is getting ridiculous.

Thanks for the advice and keep em coming

If he got you Bosh, that would explain the really good gas mileage at first, than it droping thru the floor

If you need an O2 or it'* a Bosch, I have an extra AC Delco that I will send you. Just let me know.

When was the last oil change?

just got one about 1k miles ago. I get one every 3k. My car takes 2 02 sensors. I replaced both. I think I still have the old ones and I'll have to check the garage to see if I can find them.

Make sure none of the spark plug wires are near the O2 sensor.

If an injector driver were hanging open I would expect the plug to quickly become fuel fouled. Like the others asked, are there any codes in the system? Other than that, checking the O2 brand and cleaning the MAF were some great suggestions. I think it'* interesting that you saw a jump in mileage after changing the sensor, and now see a sharp decline. If the O2 sensor is Bosch, change it. If the sensor is Delco or Denso, you should be in the clear.

How cold is it where you are and what kind of plugs are you running. Have you run fuel injector cleaner recently?