Thread: Gas Mileage down, KR is up

Ever since I bought this car last year I had been running about 19 mpg according to the DIC. Not really too concerned about economy but I keep the DIC set to display MPG since that seems to be the most useful thing to look at LOL.

About 3-4 months ago I started to see gas mileage erode into the 18's, and the motor was running rough. I have one of the Aeroforces set to display boost/vacuum, and where it usually was at -19 or so at idle it was at -5, so I had a vacuum leak. I replaced the busted vacuum tee at the LIM right under the SC snout and all was back to normal.

But the gas mileage never improved, it continued to decline, and even after a reset, the DIC is now stuck at 16.3 for mpg. I had the chance to romp on it hard the other day and was watching KR on the other aeroforce, and where I was expecting to see 1.5 or so it was at 7!!! Oh, and the mpg went to 16.1 LOL.

The only thing I have done is upgrade the wheels to 18x8 and tires to 245/45-18, but since they are same diameter as OEM it shouldn't affect mileage, unless being 10 lbs each heavier has that much of an effect. Car continues to idle rough although I can't say I notice any loss of power.

Any ideas to get me started looking in the right direction?

Pull the spark plugs and check the condition of all of them. I see you have the plain old 104s. Could be a host of things from another vacuum leak to a bad coil, clogged cat (I know you have a high flow), dirty Maf sensor, clogged fuel filter/ injectors. Check for a pattern of misfires on the aeroforce.

Thanks Rick, I had the injectors professional cleaned ultrasonically when the LIM was off last Fall, and new filter then also. Plugs could be an issues, I'll check those.