I need help. When I first got my a4 I was about 50% hwy driving and getting 330 mi per tank. Now I'm lucky to get 245. I installed a new fuel filter a few months ago. I cleaned off my maf and ait sensors with alcohol. I just put on a test pipe w nonfoulers thinking I had a clogged cat and realized white smoke from tailpipe. I don't think my head gasket is bad with no milky or foamy oil.

What other things should I check for my gas mileage.

 

Usually MAF and primary O2 sensor are to blame for bad mileage. Do all the usual stuff though - check/change air filter, verify tire pressures, grease the brake caliper sliders and make sure the ebrake isn't dragging, reclean the sensors and harness connectors with electrical contact cleaner, new spark plugs gapped to .032 if you're stock, and .028 if you have a chip, check vacuum lines for damage/dry rot/disconnections.

 

sometimes it could be your coolant temp sensor as well... it'll tell the computer that ur car is cold and when your car is cold the computer tends to give the car more gas to warm it up quicker and if its stuck on cold all the time then that could be a factor but like i said maybe thats the problem.. i would check the plugs to see if they're fouled ... hope that helps

 

Bump :/

 

Did you try any of this stuff? Any results to share?

 

Cleaned sensors, spark plugs good, air filter is new, tire pressure is good, vacuum lines look good, ..... Only thing I didnt check was coolant temp sensor because it was replaced last year but its cheap so I'm goin to pick one up anyway

 

i have a bad coolant temp sensor my cars throwing a code i forgot it exactly but i beleive its p0811 or something . but my temp gauge isnt working. well sometimes it will work prob once every 50 start-ups ive been dragging *** to get a new one just been so busy with work and my daughter but im gonna get one this weekend. can anyone give me a brief description on where it is ? or where i can find a walk threw on replacing it. i searched but couldnt find anything. my gas mileage could be better i think im only getting about 15 mpg ... thank . oh and btw my car is a 98 2.8 30v manual thanks again

 

CTS on a 30v engine is in back, down low, behind the passenger cylinder head. It'll likely be blue in color and it has a four-wire harness plugged into the top. Push down on it and pull out the retaining clip, then use the harness to lift it out. Replace it on the harness, along with a new o-ring (make sure the old o-ring comes out with the old sensor), and reseat it. Push down hard while reinstalling the clip, and before you drive, once it's in, pull up on it to be sure it's seated right - its easy to misposition the clip and if it's not right you'll lose all the coolant.

Order the sensor, o-ring, and a new retaining clip - easy to lose the o-ring and easier to break the clip.

 

Thanks man I appreciate the help. I can't believe all week long when im at work its beautiful out 75 degrees + now sat and Sunday come and its f'n raining out! Gotta love how it works like that lol

 

Ok so I changed the ect sensor today. I haven't noticed a difference in fuel economy yet but its definitely still smoking. I looked harder today and I think the smoke may actually be blueish so I am thinking compression test. Any other ideas? Is there a way to test the pcv system?