check engine light not on

[AkaiRPS13]

I know this sounds like a good thing but it worries me when the O2 sensor is disconnected. Its a 91 DOHC at 125000mi and I'm also having problems with gas mileage, a couple of times the car has stalled as though the idle valve is stuck, I also periodically hear a ringing sound from under the hood at high rpms(5500-6500). I have changed the air filter the fuel filter the O2 sensor in attempts to recover the gas mileage to no avail. I have read about what to do about the Idle valve and timing chain tensioner(i think) problem but with recent gas prices im paying nearly $30 to fill the tank twice a week so those problems will have to wait. oh yea and the light itself works, it comes on when you turn the key to on without starting the car. thanks for your help

[ninjak84]

How many kilometers/miles are you getting to the tank?Keep in mind these aren't exactly the most fuel efficient cars on earth

I don't think the o2 sensor will trip the check engine light anyways when it's disconnected, but hopefully someone can confirm that for me.

[AkaiRPS13]

it was getting about 24-27 mpg but it sorta suddenly dropped about 5000 miles ago to around 17-19. I dont always drive like a maniac. only about a third of the time im driving and ive rarely got it at full throttle. I have to say though there has been an improvement after I used redline sinthetic oil for my oil change last week. I'll have to measure the milage again.

[NISMOlvr]

I own a 92 240 sx and the check engine light MIL does not stay on with ignition on ,engine off.It does work and comes on when I disconnect tps to check timing. It does not display whith ignition on ,engine off.please help.