A4 very rough idling , fuel pressure all over the shop

[a4_co_durham]

to cut a long story short, car has 148k on it & has been mostly fine
had major service at independant last week all good
next day en route to work filled up @3/4 tank at Sainsburys (yes i know....) and after that when at some roundabout lights noticed car was rough/shaking when idle in neutral and revs bouncing about 1000prm...
seems to run fine when driving normal but definatley getting shaky when idle, no lights on dash at all
so next day popped back to garage where service had been and they agreed def something amiss, but no codes on ECU at all ?? we could see the fuel pressure bouncing about all over though? and when he disconnected the fuel pressure sensor the engine went back to normal, so suspected the sensor was dodgy, but no codes ?
anyway in the office they asked a few more questions and seems they think may be filling up has disturbed some crap in the fuel so may not be the sensor?
so not sure what to do as dont want to spend money on something they dont even know will work. said they can take the car in for a day and have a proper look but a bit vague on how much this will cost (understandibly?..) or if they can narrow down the issue

been using the Mrs car this week whilst i seek a second opinion & thought i would ask here?

could it be as simple as the sensor? as it seems ok when disconnected

cheers

[fil1973]

Tdi or a petrol audi? Post does not say,
That would help diagnosing,

Also what diagnostic machine did the garage read it with? Snap on, delphi,
Or similar, Most are a bit sketchy

Really it needs code reading with vcds or odis for proper results[emoji106]




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[a4_co_durham]

sorry its diesel ! forgot that bit :-)

im not 100% but sure its ODIS (blue handheld tablet type) it is a german car orientated garage i use, def no codes on their machine

[a4_co_durham]

MODS just noticed ive posted in wrong section

should be in in B8 - as is 59 plate A4 2.0 TDI

Ta

[Axelz2]

Had an issue with my tdi 2.0 when I’d let the tank get nearly empty and filled up from a different petrol station - could have been some gunk at bottom of tank or contaminated fuel but car was stalling and idling really roughly. Took to dealers and they were stumped and ended up swapping fuel injection/line parts over from donor car, was apparently issue with fuel pump pressure jumping all over the place and they had quoted £2k to replace. They put all back together after draining tank and it started working again, thankfully. They didn’t think was contaminated fuel but I’m not convinced.


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