HDI rough running is air temp sender important ?

[charentejohn]

Here we go again, I thought the car was sorted out but died again today. Missed a couple of times but kept going then cut out at a road junction, great.
Wouldn't restart so did the usual and disconnected the MAF, started but not happy. Got it home (2 miles) and trying to cut out towards the end, kept the revs up and just made it before it cut out again.
Left it a couple of hours and it started and ran ok, in the garage, as not chancing a road test just yet.
So I replaced the MAF with a new one, not Bosch but should be ok, disconnected battery for 10 mins and it then started ok and will tick over but......

When revving clouds of not too thick blue smoke, oil level is ok and I got no blue smoke before, and when I do rev tickover rev tickover I get clouds of blue smoke with occasional puffs of black smoke. After about 10 times doing this cleared up but I am not sure all is well. I think it is not as economical as it was either.

What I did notice is that when it was running ok, almost 50 miles before it messed up again, the temp display on the dash was correct. Now it is showing nothing, when I had previous problems the temp display was either wrong or showing nothing. Does this sensor play any part in the above problems ?
I read a few posts here on other cars that hinted it might, I didn't think it would matter certainly not enough to stop the car working ?
Any help appreciated.

[JamesQB]

I can only offer advice based on my knowledge of my VW diesel and a similar fault I had. The MAF is very important and can cause (depending on the fault with it) awful running with kangarooing and cutting out. I bought a 2nd hand Bosch for my VW to sort that problem out. On the VW forums it is well accepted that non-Bosch MAFs are not very good and can give very poor running. As Bosch themselves state regarding MAFs, there's a reason theirs cost over £100 and a reason some on eBay are only £20...

The temperature sensor on my VW if faulty can cause excessive fuel consumption and alter injection advance but nothing that is very noticeable. In fact I didn't know mind was faulty until I connected the diagnostic interface and saw it was reading about 30 degrees too low due to a high resistance corroded pin on the sensor.

I'd put a genuine bosch MAF on for starters.

[charentejohn]

Thanks for the info, I didn't think the temp sensor would make much difference just that it went wrong the same time the car did so I thought there might be a link. Even if not directly the sensor failure could be because of something else. The car is just at one of those stages where bits are failing randomly I think. Currently at MAF, 2 fuel presure sensors and two hydraulic pump seals and still not right.

I am going to give the EGR a try, disconnecting first as advised on here. If it helps I will replace or remove/clean it as not expensive.
Edited to add, disconnected EGR feed pipe as per this post http://www.frenchcarforum.co.uk/forum/v ... =3&t=46791" onclick="window.open(this.href);return false; Needless to say I only have one relay not two so took off the front one.
Seems much better so maybe that is it. Started it and clouds of blue smoke and some 'hunting' of the engine, disconnected and sealed pipe and smoke vanished and running smoothly.

Good EGR writeup from GSF http://blog.gsfcarparts.com/problems-with-your-egr/" onclick="window.open(this.href);return false; which did sound like my problem as regards when problems occurred, like once warmed up.
If this runs ok for a 100mls or more I will get a new EGR valve as not expensive. I think it may need replacing rather than cleaning as it as it seemed to be open when cold as rough idle and smoke but it should have been closed at this point. Maybe the spring is weakened so opens too early.
Now that I think back I have had some smoke for a year or so now but it only seemed to be on cold days and cleared quickly, could have been EGR slowly dying.

[charentejohn]

Spoke too soon, back to square one. Less smoke but running on and engine warning light back on again, I give in.

[Zelandeth]

Fuel pressure regulator immediately springs to mind...that can cause all manner of odd symptoms from what I remember.

Anyone near you who can plug it into a Lexia for you to see what it's saying? EM light being on shows there's a fault stored...

[coastline taxis]

is yours a early c5 with the bosch fuel system and does it run on for a couple of seconds when u switch it of

[charentejohn]

I have done the pressure sensors but they may still not be right, car is a Xantia but I believe it is the bosch fuel system and 2 seconds is right.
Disconnected battery overnight and suddenly all is well ? Car has no smoke, no light and is accelerating better than it ever has, if a bit rattly in lower gears.
Normally you would think this is great news but this is what happens, I get all confident and go 20 miles and it plays up again. Problem with intermeittent faults.
One good thing is the codes should have cleared so any the garage gets should be current.
Off to check the rear of the engine for loose/damaged pipes as best I can, not easy access but worth a try.

[coastline taxis]

change your fuel filter housing. both top and bottom parts of it

[charentejohn]

Not sure how that works but would be worth a good clean when next off.

[Peter.N.]

The pressure regulator on the HP diesel pump will cause running on and a host of other problems.

Peter