Recently whilst driving home from work I noticed that I had hardly any boost. It would start to spool up but then nothing really, no kick in the chest as it usually does when it comes on full boost. Just a faint whistle from the turbo and no dump valve sound from the cai. Now at the time she was REALLY low on fuel and it has a walbro fuel pump fitted amoungst other things so i thought maybe fuel starvation. Stopped and fuelled up and set off again. Was still the same when first pulling off then seemed to settle down and go back to normal. Then it went ok for a few days until today whilst pulling onto a dual carriageway I got a small stutter at about 3k rpm and every now and then the boost felt really on off and quite aggessive both coming on and off boost but this was intermittent.

Now ive scanned it with vagcom after getting home and got the following error:

16804 - Catalyst System; Bank 1: Efficiency Below Threshold

P0420 - 35-10- --Intermittent

Does this mean my cat is goosed? or could it be something else. To be fair its been driven like a baby for the last month or so as ive been doing more miles to work than normal so trying to save on fuel.

If its the cat then fair enough I will just decat it as I am planning on doing some more mods in the next month or so anyway but dont want to replace the cat just yet if it could be something else.

Any help would be appreciated guys.

Cheers

Dazz

log block 015&016 for misfire recognition and also 115 for actual vs requested boost.

First log will tell you if you have a problem with spark plugs or/and coil packs and second one will tell you if your MAP sensor is working normally.

When you hit soft limp mode, did you try shutting down the engine and immediately start it again? Did the car behave normally?

I only have vcds lite so can i stll log blocks?

Also yes i tried shutting down and restarting the engine the first time it happened and it did nothing. Even after shutting the car off and leaving it for 6 hours at work didnt sort it as it was still the same when I came out. Now it just seems to happen on the very odd occasion.

Unplug the MAF and take it for a spin. If there's no difference in performance or it performs better I'd say your MAF is goosed. That's the first thing I'd check. Second thing I'd check would be N75 valve.

Ive just got back from a short run with the MAF unplugged. The intermittent fault is still there and general performance is worse with it unplugged so I guess that rules that out..

Reading on the Ross Tech website it states the following for this fault code:

16804/P0420/001056 - 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
  

Possible Solutions

• Check Intake and Exhaust System for Leaks
  
• Check Catalyst
  
• Check Oxygen Sensor(s)
  
• Check Oxygen Sensor(s) Control
  
• Perform Oxygen Sensor(s) Aging Check
  

Now im running a CAI which has been fitted for a while and there are deffo no leaks there, and I cant find any leaks in the exhaust system, so i am guessing it is going to be either Oxy sensor or Cat issue?. I just dont want to start changing parts willy nilly untill I know wot the fault is as it could start to get expensive lol.

Ok so this might be related or it might be nothing. After I had unplugged the MAF last night for a test I plugged it back in and just left the car on the drive. This morning when I got in it to go to work the car was an absolute bitch to start and theres an orange light on the dash (the warning triangle with the circle round that comes one when u switch the ASR off). Now this came on when I drove the car with the MAF disconnected which I know is normal, but i pressumed it would go out again once the MAF was reconnected?

However the car drove amazingly all the way to work, far more get up and go than its had in a long time making me realise that maybe there has been an underline issue for a little while now.

Just need to figure out what it is so I can fix it..........

A couple of points:-

1) Leaks between the air intake and the turbo won't make much odds because that air's stil at atmospheric pressure.

2) Your orange warning light means ASR/ABS faulty or switched off. You've not even thought about checking that AFAICS. ASR works by pegging back the power to restore traction so if it's faulty it could just peg the power back when it doesn't have to. The switch should still turn it off, in which case if I'm right switching ASR off should restore full power.

Just strange how the orange warning light only came on when I unplugged the MAF. As of the trip home from work the orange warning light has now gone out but the running issue has returned. After clearing the initially found fault the only fault logged on vagcom was the MAF being unplugged.

So now im in the position where the car has a running issue but no fault is being logged. Im starting to think that the fault might not be related to the catalyst log and maybe is was an old fault logged from another time.

The hesitation only really now seems to occur at around 3.5k rpm and then picks up a bit but is still sluggish. It seems as its not the MAF so I think i need to start looking at some of the measuring blocks mentioned. As I only have VCDS Lite i may just pay someone to look at it for me.

So this evening I decided to check the condition and gap on my spark plugs (and also turn my forge 007 round the right way as the sound was annoyin me.) Everything looked as it should but since doing it the problem has got worse.

So I thought maybe plugs or a coil pack. So i changed all the plugs and one by one replace the coil packs with a known good one, still no change. This is doing my head in now and any help would be appreciated.

Where do I need to be looking next?

Bad lambda sensor? What are the lambda readings?

Not sure what the lambda readings are yet, the garage I use in my area who is going to take a look at the measuring blocks etc cant look at it till next wednesday. He's also going to take a look at the MAF as he still think that my be the cause.

Incidentally I unplugged the MAF again this morning for the trip to work and hey presto the car runs fine. Really startiing to think that could be the issue. Just need to find someone local with a good one that I can try to either confirm or illiminate it as the issue.