Hi all. New here. I did a search and own a (crummy) Chiltons manual but couldn't figure out what to do.

I have a '93 240 sedan, automatic. 125,000 miles. I replaced the air filter and cleaned the MAF and PCV flame trap. While doing this I decided to point the air intake behind the grill downward, allowing air to be forced into the air box at speed and pulling colder in than the air around the radiator. The previous owner says the O2 sensor was replaced.

Well after maybe 45 miles I got a CEL. The codes are as follows.

121 Mass Air Sensor
221 Heated O2 Sensor (rich mixture/part throttle)
231Lambdfa adjustment (what is that???)

I also suspect the thermostat in the air box may be faulty, but found no info on how to check it.

To my knowledge, the car runs just fine. Better than before actually. It's no rocket, but they're not supposed to be, right?

So where do I go from here? Can anyone give some troubleshooting tips or direction? Thanks.

 

So, my Chiltons manual says the 221 and 231 codes are "compensating for lean, or rich at cruise", just FYI. I guess thats correct?

 

Check for vacuum leaks and test the O2 your self with a volt meter.

 

I am fairly certain I have vacuum leaks. About every small hose, and my PCV are in poor shape (split ends and all). I'm getting new ones on the way. I tried in the Chiltons to check the O2 sensor, but got no voltage, and resistance of 4ohms no matter what (hot or cold). Maybe I'm doing it wrong? That manual sucks....

 

You were testing the voltage at the single wire correct?
If you get nothing then maybe the sensor is bad.
Also check the fuses I think one is tied to the O2 sensor.

 

I'll check out the fuses and see. Also on the O2 sensor, theres a connector with two flat male ends, and a single with a rubber boot on it. Is that the single you're talking about? Thanks.

 

Yes the single one pull the boot back and thats where you test voltage with the car running.
It should sweep between 0 and 12 volts.

 

Okay I'll try that later. Also, I cross threaded a spark plug! Guess it's off to the repair man.


Man I hope this isn't typically the way things go on a 240...

 

No its not typical!!

 

Well, lemme ask this, the spark plug is seated, although it's cocked a bit and cross threaded. The car is running like poop. Think it'll shoot out a plug in the 25 miles it takes to get to the local Volvo guy? I pulled the plug out and the gap was all messed up. I put it back in after resetting it cause I need to be able to drive to the repair guy.

 

It is hard to say it might hold and it might not.

 

Tapping the cylinder head was easier than I thought. Also, the car runs fine with no codes after the battery disconnect and code reset on the code-reader-engine-bay thingy. So far, I've actually had more luck fixing things than on any other car. (Knock on wood...)

 

Glas it is going well.