Oxgen sensors were replaced, I still get horrible gas mileage! Any suggestions?

[RudradaRudebwoi]

I have a 1993 mazda 626 es 2.5L DOHC V6 engine manual tranny.  I had Pep Boys to replace O2 sensors & fuel system clean out and I got ok gas mileage especially on highway. Now its back to horrible gas mileage.  The engine light still comes on.  Also my idle has been a little rough since the last several weeks.  I had to adjust the idle air control screw to keep it from dying on me, unfortunately it idles at 1100-1300 now.



Its been since January 2007 since Ive had engine tune up with new spark plugs and wires and up til now ive put close to 3000 miles since tune up.  Also in March I have valve cover gaskets done.  Could the oil have possibly damaged the spark plugs? The spark plug wires are quite soft now.  A friend pointed that out to me is that a bad thing? Its my first car and im so sick of putting so much money into it. I just want to find whats wrong and put an end to this.  The car is a good car though, runs nice besides this.

Thanks for mentioning.  I forgot to add that the auto shop had to replace 2 vacuum hoses as a result of erratic idle while valve cover gaskets and manifold gasket were replaced.  I would suppose that possibly there could be another vacuum leak somewhere that wasn't caught?! Hmm . . .

[MichaelB]

Heh heh, never once did you mention checking all the little vacuum hoses all over that engine compartment...one split or broken off will account for poor idle and gas mileage too...



While you're at it, check the air pressure in your tires too...off by as little as 3 or 4 pounds will give you 4 or 5 mpg less...

[dadforfive]

If the check engine light is on, then the computer stores the code that tripped it.  have the codes pulled and that will give you a good place to start.  Good Luck

[UCANTCME]

I can only say that you should get the vehicles computer scanned and check for any problems as well as codes and then you will have a good idea on what the problem truly is.