Audi problem with cold start and revs

pippip

Hi Folks,

Car: 02 A4 (B6) 1.8T (AVJ) 150k miles on clock

Problem: Last week when starting cold the car would start and idle at 800rpm
(usually this would go to 1200 and wind down after a few mins to 800)
Anyway, the moment I touched the accelerator it would cut out. If I pumped the accelerator I could keep it going & move off while keeping the revs up, once driving a few minutes all was fine. This has gotten worse now that the car wont even start until I pump the accelerator and even then takes a few times to keep it going.

While driving it goes through spells where idle is 800rpm and then randomly 1000rpm. When its at 1000rpm I can feel the car is getting slightly more gas as I drive (revs don't drop as quick and accelerates faster).

I've scanned for codes and am getting 16804 (P0420-002)
Catalyst System; Bank 1: Efficiency Below Threshold
Possible Causes
Leakage in Intake and/or Exhaust System
Catalyst faulty
Oxygen Sensor(s) faulty
Oxygen Sensor(s) Control faulty

Car is all fine apart from this, temp is fine, performance is smooth, no strange smoke or smells. Once warm or even remotely warm it starts no trouble at all.

Any advice welcome.

jimgoose

Like the diags say, this reads very much like a vaccum leak somewhere in the intake. Possibly a split hose? This will probably lead to an NCT emissions failure as well.

pippip

I'll have to have a look around under the bonnet. I'm thinking faulty sensor now as today it randomly started fine from complete cold start. Just so annoying as it drives fine once going, apart from random slightly higher revs.