88 NA with no O2 sensor...
 

I'm thinking it doesn't have an O2 sensor as I can not locate it.

It has a Racing Beat header and full custom dual exhaust.

What would some symptoms of a bad/missing O2 sensor be?

The O2 wire is a single braided covered wire that comes off the harness near the back of the TB.

I think the reason why you do not have one is because that wire needed to be extended to put an O2 on your header and it wasn't done.

Racing Beat puts the O2 sensor bung in different places, so it's not all that easy to find. Also, some of their headers don't have a bung. The best way is to follow the wire as suggested in the previous post, although this will not work if the wire is not connected.
http://www.racingbeat.com/images/items/16128.2.jpg
http://www.racingbeat.com/images/items/16130.2.jpg

If you can't tell any difference, then what does it matter? ;)

Typically, your check engine light will be on and your gas mileage will suck. RX7 gas mileage sucks anyway, but no 02 sensor makes it even worse in light throttle/cruising situations.

in most cases you will not even notice a difference if it is gone or there working properly. it's job is very limited, unlike on todays cars.

I agree with you to an extent. I rolled with the 02 disabled on my car for a few weeks and noticed my gas mileage decrease quite a bit.

One thing I did notice though is that under very high vacuum and very little throttle (like say, cruising in 4th gear at 50mph) the port air injection is on and the ECU is in fact ignoring the 02 sensor.

It's getting crappy mileage... 13-17 usually... Sometimes less.

thats pretty average actually

blah...

im getting like 146km to a tank thats not average is it

sounds low even for 100% city mileage but city mileage can vary quite a lot to that even being a high number, so if that is 100% city mileage then your question cannot realistically be answered.

do a full tank on the highway for a real mileage consumption test.

that was both city and on the freeway i have went through 2 full tanks and the results are the same

definitely low, maybe your leading ignition has gone on vacation.

so what would be a good solution to this problem

check to see if your front coil is firing with a timing light or an insulated pair of ignition wire pliers.

When I hook up a timing light, about 50% of the time it's on mark, the rest of the time is split between off mark, to can't be found...

do you no where a good supplier is to buy new ignition coil

nope. do you? lol

bought coils from a guy on here, no improvement...

so my coils seem to be fine any other reason i could be getting bad mpg?