Have just bought the above car and have noticed that there is a problem when the car idles or is accelerating from under 2000rpm. Basically it's rough.

I have started working through the possible problems. I don't think it has anything to do with the lpg as the same problem happens on gas or petrol. There is no difference. The engine management light is on all the time and sometimes flashes. This could be something to do with the gas and a diversion from the real issue.

I have changed the plugs to Nismo iridium units and have replaced 2 of the coil packs. I have also swapped the ones I took out over to see if they were the problem, no, but it is better. I have also cleaned out the air filter and MAF.

I did notice that there was no anti-freeze in the radiator when I picked the car up, so have chaned it too a 50-50 mix.

Looking at some other threads there appears to be a few potential causes. Anyone got an idea on the best place to start from now?

Apart from that the car really flies. I drove it 650 miles home yesterday and got 29mpg on gas which is around 65mpg petrol equivelant.

Have you had the car checked with diagnostic equipment, eg VAG-COM, to see if any error codes have been logged? And for antifreeze, have you used G12 or the later G12 Plus - both of which are specified for VAG alloy engines?

No, I don't have any diagnostics and have not had time to get it checked at a garage.

I used g12 plus antifreeze.

I have ordered a vag-com cable so will be able to get some codes next week.

In the meantime, I have an idea it could be the MAF. the one on it appears to be a reconditioned unit and has the following marked on it, "reconditioned unit - bosch code 0986 280 217. Yet when I look this up it does not appear to be for that engine. the one quoted for the ARX engine I have is 06A 906 461. I know Bosch and VAG have different codes, but I can't get these to cross reference.

Looking at the list of problems, they appear to point towards the MAF. The engine idles poorly and sometimes dies away; it is poor to accelerate until 2000pm and the engine managment light is on.

I also disconnected the MAF last night and drove it around for 5 minutes with it off. There was no difference at all. It was exactly the same when I reconnected it and ran it again.

That seems pretty diagnostic of the MAF.

Mind you, I'm a big fan of NGK plugs (since curing a problem with a Pinto engine cooking plugs in 4_000 miles a set by switching to NGKs). Well, unless one of the tuners would recommend a different brand for the 1.8T?

Thanks, I'm pretty sure as well now, but I'll wait for the vag-com cable to confirm. Are there any give away codes?

I used Denso iridium plugs since I remember reading somewhere that you should use the best possible plugs with lpg as it tends to produce higher temperatures. Don't know if there is anything in that of course, time will tell.

One of the things about MAF faults is they don't always throw a code.

You can use the measuring blocks though to see what the output signal from the MAF is.

One of the things about MAF faults is they don't always throw a code.

Yep, If its on its way out I can vouch for that one

Have just bought the above car and have noticed that there is a problem when the car idles or is accelerating from under 2000rpm. Basically it's rough.

I have started working through the possible problems. I don't think it has anything to do with the lpg as the same problem happens on gas or petrol. There is no difference. The engine management light is on all the time and sometimes flashes. This could be something to do with the gas and a diversion from the real issue.

I have changed the plugs to Nismo iridium units and have replaced 2 of the coil packs. I have also swapped the ones I took out over to see if they were the problem, no, but it is better. I have also cleaned out the air filter and MAF.

I did notice that there was no anti-freeze in the radiator when I picked the car up, so have chaned it too a 50-50 mix.

Looking at some other threads there appears to be a few potential causes. Anyone got an idea on the best place to start from now?

Apart from that the car really flies. I drove it 650 miles home yesterday and got 29mpg on gas which is around 65mpg petrol equivelant.

How many miles on the clock throttle body may need cleaning

98k on the clock. My vag-com cable arrived today, so I'll see what if any codes it throws up.

You will have a code on the MAF now anyway though as you have driven with it disconnected. If it drove the same with the MAF disconnected then I'd be more inclined to say it's not the MAF as when it's disconnected the ECU relies on readings from the other sensors and tends to run better but slightly richer IIRC.

Ok, I have finally got my vag-com working and have the following 7 codes listed. I only had the basic version, but by hunting this site, I found all but one of the others.

Fault 1 - 16684 (p0300) multiple cylinder miss fire detected.

Fault 2 - 16685 (p0301) missfire on #1 cylinder

Fault 3 - 16686 (p?) missfire on #2 cylinder

Fault 4 - 16396 - (p0012)Camshaft Position Actuator A - Bank 1 Timing Over-Retard

Fault 5 - 17705 (p1297) Throttle Valve pressure low.

Fault 6 - 17608 (p1200) Boost Pressure Control Valve ?

Fault 7 - 16486 (p0102) MAF Signal too low.

So, can we discount fault 7, as I stupidly disconnected the MAF?

Are faults 1, 2 and 3 the same? I have since changed the coil packs on #1 & 2 cylinders.

I read elsewhere that fault 6 can be generated falsely?

So that leaves me with 4 & 5, i think.

I've cleared the codes, will go for a drive and check again for codes as advised elsewhere.

Ok, been for a drive,

17608 is still there

17705 is still there

16684 is still there

16685 is still there.

Any thoughts anyone?

Get 1 replacement plug, or one from the old set if you kept them (I always keep an old set for a petrol engine). Put it in No1, and see if that helps with the misfire. It wouldn't be the first time (nearly, but not quite) someone went chasing a fault that was actually a bad plug in a new set.

Get 1 replacement plug, or one from the old set if you kept them (I always keep an old set for a petrol engine). Put it in No1, and see if that helps with the misfire. It wouldn't be the first time (nearly, but not quite) someone went chasing a fault that was actually a bad plug in a new set.

Or could you swap the plugs round to see if the misfire moves to a different pot

Have now completed all plug and coil swaps. I have also decided to run the car on petrol only at the moment to rule out any duff codes from the lpg. I am still getting these 3 fault codes:

Fault 1 - 16684 (p0300) multiple cylinder miss fire detected.

Fault 2 - 16685 (p0301) missfire on #1 cylinder

Fault 3 - 17608 (p1200) Boost Pressure Control Valve ?

One other thing I noticed was that the plugs on 1 & 2 were coated in carbon having only done 200 or so miles. 3 & 4 were fine. I put them back where they were.However, after giving it full revs a couple of times, I took them out again and noted they were less carbonised. Almost like giving it the beans was clearing out the system.

As a stingy git, I was wondering if anyone had any views on shooting some 10k boost up it to see if that cleans it out and more. I have also ordered Forte specialist injector cleaner which I plan on adding to an entire tank of petrol and run the car on that until it goes.

I get the feeling that the plugs and injectors could have been gunked up because I have read in a few places that unleaded goes off after a few weeks or months. If this was the case, could this accelerate the carboning up?

If all else fails, I'll hand it over to my grease monkey to change the injector on No 1 cylinder and check out the third code to see if that is a spoof or what?

Carbonised plugs - hard glazed carbon or soft sooty carbon?

Soft sooty carbon suggests the engine's running too rich.

A hard glaze suggests something oily is getting cooked, which suggests you've got the wrong temperature grade, and some oil from somewhere.

Are these results from running on Petrol or LPG ??

If LPG I would suggest re running it on Petrol to see what differs

soft and sooty carbon. Too rich then? Cures please?

I dont suppose the cars been remapped, just a thought if its running rich

If you suspect injectors as one pot seems worse can they be swapped between cylinders & see if the problem moves to another pot.

Check the lambda sensor readings; should be 0.7v on steady throttle.

thanks, I'll check the lambda. How do I check to see if it has been remapped?

In any event, I have now shot a whole tin of 10k boost up it with mixed results. Again, it is smoother, but the same three codes still come up whether on petrol or gas:

16684, 16685 & 17608 which supports the injector theory. I'll get them swapped over soon. The car is going in for an lpg service tomorrow, so we'll see how that goes. After that, it will be over to my grease monkey for the rest.

A big thanks to all.

More info, I spoke to the LPG garage today. They advised me that the miss fire cannot be linked to the injector as the petrol and lpg systems have their own injector and the problem exists on both. Therefore, the problem appears to be electrical. I will scour the forums for information on a miss fire from an electrical fault.

From the foregoing, it doesn't seem to be a plug or coil pack yes.

Having ruled out the injection (presume both systems use port injection?), I think we're looking at the TDC sensor (but why only a misfire on cylinder 1 then?), EMS hardware or software. Is there an EMS re-program associated with the LPG system?

From the foregoing, it doesn't seem to be a plug or coil pack yes.

Having ruled out the injection (presume both systems use port injection?), I think we're looking at the TDC sensor (but why only a misfire on cylinder 1 then?), EMS hardware or software. Is there an EMS re-program associated with the LPG system?

Totally different train of thought, Would poor compression cause similar problems, ie smooth running at high revs but lumpy at low revs, my scoob certainly ran like a bag of pooh on 3 pots but smoothly at full revs although it was leaving a smoke trail a red arrow would be proud of due to a holed piston. If the valve seats were leaking that would not neccesarily create any smoke but would drop the compression. When we rebuilt my 1.8T a couple of the old exhaust valves were cracked. I know in the early days of LPG a lot of cars suffered with head problems, as I said a totally different train of thought & one that the more mechanically qualified can probably comment on / dismiss. A simple compression test should answer it if theres any doubt