My engine light is on. I changed the o2 censer. What could it be?

perhaps the code has cleared? Try unplugging O2 sensor and starting / removing 1 plug wire etc. to induce code to verify light?

Its going to be tough to find the problem without access to a 4 gas machine. Especially if there are no trouble codes in the computer.
If the fuel mixture is rich it should set a code for one or both O2 sensors. Same thing if the EGR is not working, etc.
One thing that could cause problems is the thermostat not getting the engine up to normal temp.

i had a high idle problem on my Chevy blazer.there is a air mix censer that controls the idle,it cost a $100.00.I changed it and fixed my problem.IBOUGHT A SHOP MANUAL AND IT TOLD ME ABOUT THE IDLE CONTROL CENSER!

Check the O2 censer. its probably bad.

might be fanbelt

At idle or higher rpm...on a test ? With a scanner you could look at the STFT ( Short Term Fuel Trim.)

This would give you an idea how much adaption is being applied to the fuel delivery.

Any number above 12% will cause CHECK ENGINE ( MIL) to come on.

This problem can have several causes. Most common would be too high fuel pressure.

Next would be faulty injector/s.

Next would be restricted exhaust system.

Another would be coolant running too cool.

Lastly catalytic converter efficiency too low. Although this should trip a code for that part of the emission system.

Of course it doesn't stop there, the resistance in a sensor can be out of range or resistance in the wire loom connectors and/or battery ground cable connection resistance and also alternator problem feeding too much A/c ( Alternating Current, known as ripple.) into the charging system.

So...as you can see it will take some diagnostic time to identify your problem.

Try here for a shop near you that might help...http://www.iatn.net/shopfinder/

could possibly be your catylitic converters are plugged up when that happens you get no power when you step on it

could be a misfire , get checked and find out which coil is misfiring, hard shifting - if there is an E instead of a D in ur shift diplay on ur dash then tranny problem

O2 censer?

Have you tried putting some gas additive like sea foam into the gas tank prior to filling it up? It may be a bad or clogged injector.

When is the last time you did a tune up, spark plugs, spark plug wires, distributor cap with rotor etc?

Is the engine surging in rpm? if so, try replacing the mas air flow censer and or O2 censer.