my daughter has a 01 Beetle, 2.0L and its throwing up P0171 fault code, System Too Lean Bank 1

I have checked airfilter, infact put a new one in and reset let, it stayed off for a while then back on, then off then back on again, I have now Cleaned MAF and replaced, initially for 10 mins ran absolutley awful, hardly any power and horrible, but then driving ok. still seems to have low rev power loss, and a little lumpy on tickover.

even if light stays off any suggestions to the sluggishness?

also noticed that the dipstick tube was missing so no tight fit for dipstick, one ordered yesterday to remedy, could this cause vacuum/pressure issues with engine?

thoughts please gents?

many thanks