Misfiring - two error codes

[simc66]

Hi all, as a newbie I thought I'd check here in case I can narrow this problem down a bit.

My 16v has started to misfire at around 2K revs, quite badly.  The problem is worse when it warms up.  It starts and idles with no problem.  I whacked a code reader onto it and got

00519 MAP Sensor out of range G71
00525 O2 sensor voltage low G71

I've read around the forum and the 519 error would appear to be either (a) the #30 ECU relay or (b) the vac pipe from the manifold to the ECU.

Question is - what would you go for first? (the pipe appears to be OK, but I haven't looked in daylight). 

The O2 sensor isn't likely to be linked to the misfiring problem is it, or is it a symptom of the first fault?

Any help very welcome!

[Leon27]

The vac pipe for the ECU comes off the back of the inlet manifold, pull it off and give it a few sucks until you can feel it holding pressure. If it doesn't then the pipe has probably split somewhere - free and first check

The ECU relay is rubbish, I'd change it for peace of mind for the future but if your misfire goes away after 3.5k onwards then I'd definately change it.

The O2 sensor fault could be related, I'd delete both faults, drive it making sure you get the misfire to occur a lot, and see what comes back You can unplug the O2 sensor (connection on the rear engine mount) and drive it about to see if the fault is still there. Tbh, if its a harsh misfire as you say I'd be inclined to donor a #30 relay to test first

[simc66]

Cheers! - I'll give it a go tomorrow 

[simc66]

No luck - vac pipe fine, relay fine, unplugged the lambda sensor- no change.  Drove around for a bit, deleted the codes, tried again - same codes.  She's off to my friendly indie VW specialist in half an hour - will report back in case anyone's having the same problem...

[simc66]

Fuel pressure regulator hose.  Ah well, at least it was cheap

Cleaned out the throttle body as well, noticeable difference!