My 1.2 6V 9N Polo that keeps giving me P0171 code. Drives for hours before EML comes on, no loss of power (what there is of it), runs & drives as normal.  I've checked all the pipes on the inlet side, changed the fuel tank vent valve, cleaned the MAF (the one just below the throttle body), and the throttle body itself, cleaned & checked the crankcase vent valve, diaphram all good.  Disconnected the battery so it re learns.  Is there a MAP sensor on this engine? (Running out of ideas here) This is the only part I haven't actually located. Any suggestions welcome  Thanks in advance.  Chris

The MAP sensor is what you have found just below the throttle body I believe. No MAF sensor on these engines.

Check for leaks just beyond the PCV valve. The pipe that conveys its output back into the inlet manifold has some rubber coupling bits that can rot through and leak. This is a phone-camera view of just such a leak taken from below looking upwards.
 

Edited 26 May, 20224 yr by Pete1

Thanks for your reply, I can't figure out where on the engine in your pic is, possibly it's the metal pipe that has a rubber section each end from the to cam cover to the inlet manifold?  There;s also one from the vent valve (disc shaped), cam chain end of engine?  Cheers, Chris

PCV valve = crankcase vent valve, near dipstick.

This is on a BMD engine as far as I remember. Not sure how similar a BBM is.