Can AMM fail without CEL?
 

Haven't had codes read but no CEL has come on. I made a post about car running rough and using gas. It's still doing that some days better than others, but now anytime I get on the gas hard causing a trans kickdown, motor surges and lulls, surges and lulls, rhythmically. NO high-end power but all seems normal in city and even moderately-hard driving, just not when higher-RPM pwoer is called for. Tach does not jump/recede, doesn't seem to be a trans issue/slip. Definitely stumbling when power is needed. Also, motor bogs pretty noticeably now after a gear change if I step on the gas.

Mine just failed recently and I had the same symptoms for quite awhile...a big loss in power and the car stuttering..forget about kickdown..it didnt know what to do...then finally 3 months later the check engine light came on and it gave the MAS code.

Your MAS is cooked for sure.

Cool!
 

Well, not cool, but I've had one fail in 2 of my former VWs and it caused similar issues. I'll feel more confident buying one now - thanks for the reply.

My AMM failed without throwing a CEL, but the fuel trim adaptation codes were close to the threshold for throwing a light, so I'm sure it was coming. Loss of power and stumbling at 4000rpm and above is a classic AMM failure symptom. However, before I threw a part at it, we read the adaptations and installed a "known good" AMM and only after confirming the problem did I buy one and install it. Change your engine air filter while you're at it. Keeping your engine air filter fresh will greatly extend the life of your AMM. I got 160,000kms out of my original one by keepign the filter fresh and regularly cleaning the air box.

Thanks. I'm gonna get one from Phil within the next week. My hunch was AMM, really classic symptoms as you described. AFAIK it's original anyway, 104k. I do change the filter every 10k and vaccuum it at 5k, including the airbox. But I didn't own it for the first 61k.