My 98 V70 T5 233k will almost stall at a stop, idle drops to 500 or less then surges back to normal and will idle and drive fine until the next stop. I've cleaned the trottle body , replaced the MAF with new Bosch unit, spark plugs, wires cap and rotor and replaced the IAC valve with another, I have several used ones on hand. This poblem went away for a while after replacing the MAF but has now started up again. The code p0171 has been a real pia I've checked and or replaced all the visable rubber vaccum line connectors that can find in the engine compartment. Any ideas on where to go next?

 

Most likely a vacuum leak; have you tried the carb cleaner spray test at idle?

http://engine-codes.com/p0171.html