Erratic idle when cold

I recently left car outside garage overnight.
Car starts fine place key ignition fuel pump primes etc,
However the idle was jumping below 500 to 700 for 5 mins slight foot on accelerator smoothed it out no misfire.  During warm up I could hear a slight thumping/tapping noise from tank or maybe accumulator, like an air lock, actually it sound more like gloop gloop noise if that makes any sense lol. Is this noise normal during start up ?
How can I check the in tank pump is working fine because I also do notice the main pump whine is still quite audible even during driving. 
Could the filter on the in tank pump be mullered ? 

I have read about AAV valve but is that  not normally with high revs after warm up? 
How often do the AAV stay stuck in closed position even when warm ?

Thanks in advance 

if you take one of the wires off the main pump under the car listen for the lifter pump prime with ignition on. if nothing its dead or a wiring fault. but even if it makes a noise it could still be duff to check pop the feed line off it and run a pipe from there into a bucket, turn ign on and make sure it sprays fuel out

to get to the lifgter remove the seat base and theres a black metal disc, take that off and theres your lifter pump

Thanks ! Will have a look when car returns bak from Waxoyling !