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I think my mx is running a little bit rich, any ways I can help this?

Do you see black smoke coming from you exhaust pipe or black soot collecting on your rear bumper? If so, you might have a vacuum leak. Check your intake hose for cracks.<p>If no smoke or soot it's probably nothing to worry about.

sut on the rear bumper, just above the pipe

If your mileage is high its more likely oil crudding up the bumper.

Yeah it does have kinda high mileage...

Switching to heavier weight oil might help cut it back. Since its not the correct weight oil though you maybe shortening engine life a small amount. If your car has 150,000 miles I doubt the oil would shorten it so much it would matter. If you don't mind it then stick with what your doing.

As your oxygen sensors get older they will cause the car to run richer and affect the gas mileage.
how old are the O2's
Andy P. 93 GS

About the oxygen sensor, when replacing one Im guessing the old one is really siezed in there?

I just did The O2 sensor on My car and yah it took a hell of alot of force to get it out

what are you using as an intake? CAI, stock? Check the clamp at the airflow meter. If it's too tight it will distort and cause you to run rich because it's restricted from opening properly. It's free to fix so start there just to see. I spent a week trying to solve a rich running engine problem just to have my VAF torqued 1/4 turn too tight. Had I known I coulda had it fixed in 7 sec insted of 7 days.