ive got a 93 del sol,factory stock with d16z6 auto.it was getting around 35 mpg,and in the last couple of years thats dropped to 30.it has new distributor,plugs,wires,air cleaner,fuel filter and 30 PSI air in the tires.it doesnt have any issues such as smoke from the tailpipe and runs fine with 177k miles on it.should i consider changing the o2 sensor or is something else the problem?(original o2 sensor)

 

O2 sensor definitely wouldn't hurt

 

+1 14 y/o o2 sensors ptrobably should be changed

 

Exhaust Leak !!!!!!!!!!!!!!!!!!

 

have you had the fuel injectors cleaned???

what kind of gas are you running?

 

cleaned last year,i run 91 0ctane gas from 7-11

 

Hmm.....

get the motor compression checked..

Also how is the tranny doing...

most honda auto trannys i have had have major problems with higher miles..

 

Good choice on 91 that would have been my suggestions, autos are known for not so great mileage, pop your valve cover off you might have alot of build up. try and sea foam it

 

+1 on sea foam, carbon on top of the valves? suck some sea foam down a vacuum line, like the one coming from your brake booster, and in the oil

 

tranny completely redone by AAMCO a year ago,lifetime warrantee.they were probably high fiving when i left the shop...lets see if they still feel that way in 15 or 20 years(last car was a 1966 pontiac that i restored and kept 23 years).i had the valve cover off and it looked o.k. in there,oils been changed every 3k.