A4 1.8T (LPG) with seemingly undiagnosable engine running fault

[merolyn]

I've got a 54 plate A4 1.8T. 4 months ago the engine started making more noise than usual when over 40mph. This has got worse over time and the engine is now making a constant noise - sounding like a boy racer revving it up or driving in too low a gear, although the rpm counter is fine. At the same time, whilst idling the car intermittently does one of the following three things; is fine, is lumpy or revs to just below 3000rpm (it hits about 2800 then falls back to normal then revs up again), not going back to normal until engaged in first and driven off. During this time it has been in to three different garages - an excellent local non specialist, the LPG garage where it was converted two years ago and an independent audi specialist. None could diagnose a problem, though the latter two both thought an airleak could be the cause, but could not locate one. The LPG garage totally isolated the LPG and we drove 1000miles on petrol, but it made absolutely no difference. The LPG system was thoroughly checked over and they are confident it has nothing to do with the problem. Neither of the other two garages believe the LPG to be connected. The audi specialists also changed the throttle body, but it made no difference.

In the meantime (over about 4 months) we have (had to) continue driving the car, although the noise while driving has progressively been getting more aggressive. Two weeks ago the oil pressure light came on, although the oil level is fine. This happened to coincide with the timing for a service anyway (mileage is quite high at almost 120,000miles), so we took it to an audi dealership and asked them to look at the same time at diagnosing the running faults. The dealership said that the air breathers were completely blocked and that this was most likely the cause of the problem. They quoted £517 to change the air breathers and valves. Not being made of money, I took it back to the audi independents who changed the breather from the oil sump - which was slightly corroded, not totally blocked as the dealership claimed - and cleaned up the other breathers and valves. The oil pressure is still showing a fault, although it is only very fractionally under what it should be. The dealership say the sump must now be changed to eliminate the possibility that this is causing the running faults, whereas the independents say that there is little point throwing 400-600quid at the oil sump when this is so unlikely to fix the running problem, especially given that the pressure light only came on very recently and the specialists they have spoken to have said that this could not be the cause of the range of symptoms the car is presenting.

Had we left this with the dealership we would have spent £1100 already and quite possibly would only have some very shiny breathers and a new pump to show for it.

The independent place is at a bit of a loss, but have suggested changing the timing belt as someone they have spoken to says they've seen something a bit similar before.

What I really need is some advice as to what the feasible causes of such a range of symptoms could be. We can't afford to keep throwing money at things that aren't fixing the problem.

Any suggestions? Anyone seen similar problems before? I have read elsewhere that the timing belt can be a problem on the 1.8 diesels, but could this be the cause of our symptoms....?

[docurley]

Sounds like you have a sludge issue if the oil light comes on which may be caused by not using fully symthetic oil which will mean a new oil pump and pickup pipe oh and a engine flush.

Sounds like the oil pump as gone lazy from the extra strain of the blocked pickup pipe and it is this that is causing the oil light to come on (had the same issue with my old A4.

[merolyn]

Could the oil issue really be the key problem given how long the problem has been building before the pressure light came on and that after cleaning out/replacing the breathers the oil pressure is so close to being fine?

[merolyn]

The independent garage are suggesting changing the timing belt - could this be it?

[bez101]

The independent garage are suggesting changing the timing belt - could this be it?

the belt wont cause oil preasure but as above sump off new pump an pick up pipe good flush very common 2 have let go on me full rebuild both times as for your noise no idea when mine was reving high i tracked it to leal took 3 weeks ended up been a very tiny hole in the inlet pipe

[Alan02]

Seems 2 problems reading thru your post.Re: not running correctly,before i got to the point on an Induction Air Leak,thats what i was thinking too.I had a VW LT35 with the Merc.petrol engine with an LPG conversion,and i had a fault code refering to Unmetered Air,which is the engine drawing in extra air it hasnt metered.It was a few bolts loose on Manifold.It could be an Inlet manifold gasket etc.The oil pressure problems are well documented on the 1.8T.