random convo starter - what's the most frequent cause of the p0171/2 codes?

It can be so many things. The service manual doesn't suggest any one over the others, and I can go through all of them one at a time, but maybe everyone's experience here (all three of you) will suggest one to start with. WTH?

Mine drives fine on the highway. Noticed a slight shudder at idle and found the pending 0171 code.

 

I understand, but maybe the opposite of someone's frequent cause of a 71 is the cause of a 72. IDK. It's just a random survey. I don't think fuel pumps are a common problem, for example, but maybe everyone tells me they are and I start with the pita fuel pressure test versus, say, cleaning the throttle body. IDK.

 

All true, and understood. Let me see what the FB groups say.

 

I sprayed my sensor down today actually, although I didn't start it afterwards - have the battery charging. Will do that tomorrow. However, I think I did that when it first acted up a month or so ago - the spray was in the front seat of the car. Haven't looked at it since then. probably should swap over a known-good MAF sensor.

Someone else suggested the PCV hoses - that was good, the kind of thing one wouldn't typically think of first as a failure point, but in fact, I've pulled mine off the throttle body many times, and wouldn't be surprised if there as a crack in the hose somewhere. Looks like a PITA to inspect them however. On this car, the one towards the front of the car has a lightweight wire clamp holding it on the throttle body, while the one on the back side doesn't have a clamp. Is that right? The clamp doesn't look strong enough to matter.

How can I check whether they have any cracks/leaks without taking them off the engine? Would plugging the outlet at the throttle body or on the hose itself have a noticeable affect? It does stumble a little at idle, for sure when cold. Drives at speed without a problem.

thx