Hello! New to the board, new to 4Runners! I had an ''87 SR5 Pickup and still have a ''78 Cruiser but that''s another matter.

Anyway, I just bought a ''94 4Runner from a little used car lot. Its got 170K on it and it ran fine for the hour or so I drove it before I bought it. I get about 40 miles down the road and the check engine light comes on!

So I ran down to the local Checker Auto this morning and had the kid from the counter stick their OBD meter on there. He said it came back with Code 26 "Mixture control continuously rich."

I'm hoping it Is a bad O2 sensor or idle sensor. Does anybody know the most likely culprit before I start the "trial and error" method?

Thanks!

 

The code is basically saying that the engine is running rich and the ECU has to continually adjust the mixture leaner in order to keep it correct.
I'd think it's something other than the O2 since the ECU is apparently getting a signal from it, but I wouldn't rule out the sensor entirely. Possible causes of rich condition include failing temperature switch, leaking fuel injectors or cold start injector, mis-adjusted throttle position sensor, sparkplugs/cap/rotor/wires/coil, dirty air filter... the list goes on.
Start with the easy / cheap stuff like air filter, plugs and wires, set the timing, etc. and reset the ECU trouble codes by disconnecting the battery for a minute or so then go driving.
There is a link to the field service manual at the top of this forum topic list which can serve as guide for troubleshooting the various engine components.

 

I agree.

Give it a full tune-up. Then also adjust the AFVM.