My 92 model 240 has been throwing the Computer code 1-2-1...."Mass air flow meter signal faulty or missing".

That is the only code that's it's storing.

I have changed out the Air Mass Meter with (2) known good meters, and the same thing keeps happening.

I reset the computer, change the Meter and this happens
The engine will start, idle very roughly and hesitate on revving.
If I rev past 2000 RPMS, the engine will clear up and run strong.
After about 5 minutes, the check engine light will illuminate, the car won't idle and runs rough.
Code 1-2-1 every time...and that's all.

The engine will still run strong above 2000RPM.

Any idea if there is another combination of faults that can trigger this code?
I've got a hunch that the throttle position sensor may play a part.

Unfortunately I have my wife's 94 model 940 in my shop with the heater hoses removed (on order), and the temperatures have been in the upper teens to the low 20's for the last few days, and I'm too old to shade tree anymore.

Any idea is appreciated.

Hi Steve,

Saw your post on TB and sent you a PM. Check for false air.
--
Art Benstein near Baltimore

I have never hated a man enough to give his diamonds back. - Zsa Zsa Gabor

Yes Art,

I was thinking a bad pin or pushed up one in the connector itself.
A couple AMM’s made me think of the connector as a common denominator to all.

Your air comment Very well could be a bad air leak behind the AMM but wouldn’t that fall under rich/ lean code too.

I don’t hang out on Turbo Bricks to know more.

We or I need more background, if he has it?
Hope you had a good Christmas and a New year of fun and games!

Phil

Phil,

Steve's post on TB is essentially the same. He feels he's addressed the usual electrical connection and part failure causes of 121. He gets the usual "helpful" responses to address the electrical connection causes, but until after I posted here and in a PM there, no hint it might be air not being measured by the AMM. Typically this is the common problem where the corrugated hose between the meter and the throttle body has worn a hole in it where it rubs on the battery cable or strut tower. It could also be a manifold gasket falling apart, or the flame trap (PCV) plumbing. Any place the combustion process can obtain air without it passing the heated platinum wire that's supposed to measure it. Root cause could be an oil leak which has softened motor mounts.
--
Art Benstein near Baltimore

Only Irish coffee provides in a single glass all four essential food groups: alcohol, caffeine, sugar, and fat. - Alex Levine

Art, you called it.

After thinking about the advice, I began to realize that a major air leak on the intake could cause all the trouble.....and especially behind the Air meter, where it could cause a false signal from the meter.

It reminded me of all of the old K-Jet cars that I have owned, how they used to backfire and blow the rubber bellows off of the fuel body.
That was exactly the way my car was running.
I finally got the car in out of the cold, and a quick inspection revealed the hose from the Throttle control valve to the throttle intake had become disconnected.
This was setting a AIr Meter fault code in the Jetronic, and also making the car run like crap.
I reattached the hose, reset set the computer codes and the car was suddenly well.

Apparently the engine had backfired through the intake and blown the hose off.

It was like getting money in the mail.
What a relief ......look for the simple things first.

Thanks for the responses.