Lean condition, stumble, rolling idle

Only complaint with performance with this '98 1.5L manual was that once warmed up, it might stumble slightly initially on hard acceleration, and a few seconds after coming to a stop the idle would cut back, the motor would shake a bit, then roll up and down for a few seconds, as if trying to regain an equilibrium for idle speed.

Not a huge deal with a manual, but would be really annoying in gear with an automatic, might even make it die.

Then last week the Check Engine light lit, and it coded for Lean Condition, Bank 1.

The only thing that stood out in the data was the pre-cat o2 sensor reading seemed like it was kinda stuck at idle, not throwing nice up and down feedback waves...and the fuel trim indicated it was trying to richen the mixture considerably, but according to the lean code, was not succeeding in correcting the problem.

I was going to start with just replacing the o2 sensor and see what happens...but as I was trying to unplug the connector, I just happened to notice a nice big split in the intake duct between the MAF sensor and the intake. Right in a crease of the pleated section.

So for now, I just sealed it up with some high temp silicone and let it set up. Took it out for a drive a while ago, and it runs perfect. Will replace the duct ASAP.

Apparently it split from being stretched and twisted when the air filter was being serviced before I bought the car. Probably by some twonk at a Jiffy Lube or something.

Anyway...good thing to check first before chasing a lean condition...if anyone's interested.