I have a 1985 4Runner SR5 with 22RE and 5 speed manual. Last week i got the emissions tested and it failed. The CO levels are too high meaning it ran way too rich. What happens is when the motor runs at close to the same RPM for a certain amount of time, the check engine light will come on and it will go into open-loop. It will burn a lot of gas and run too rich, and that's why it failed. Every shop I called said something different and they all want about a $100 diagnostic fee just to see what's wrong. Some shops say it was the O2 sensor, the cat, or the spark plug wires.

Any input?

 

You can check the O2 sensor , and plug wires with an ohm/voltmeter. check the MAF

 

If your truck has the original cat and 02 sensor, then you should replace both. I would start by replacing the 02 sensor first, thats what the computer uses to moniter the air fuel ratio, and if its bad it could be sending the wrong readings to the computer causing the engine to run rich.