Audi A3 1.8T - Juddering, bad idle

Honest John Back Room » Technical matters
What is life like with your car? Let us know and win £500 in John Lewis vouchers | No thanks
View Threaded
Thu 24 Jun 2010 13:16
Audi A3 1.8T - Juddering, bad idle - Nick Mazda 6 TS2
have a 99 Audi A3 1.8T petrol (AGU engine) the car has just done 100,000 miles

I have recently been having an intermittent problem.

I can be driving along normally then for no apparent reason when I accelerate the car hesitates and feels as if its missfiring, it lasts for varying amounts of time then disappears. When the car is stationary with the bonnet up I can see the engine appear to misfire causing it to jerk every so often causing a popping/spluttering noise from the exhaust. This doesnt always happen so cant put my finger on what it is. It doesnt seem to be there when travelling at motorway speeds, only when I put my foot down to pick up speed. A couple of times I have been sat at lights and the revs drop to almost stall point but then it corrects itself. last week it was really bad causing the mpg reading to drop to 14mpg but has gradually risen back to normal since then!

My dad is a retired police mechanic and he cant figure it out. He has a snap on diagnostic machine which doesnt pick up any problems, neither do I get any warning lights on the dash.

I have been trying to fix the problem but I am running out of time, money and patience as it isnt a consistent problem.

Not sure if it means anything but it has been worse since I serviced it a week ago, I changed the oil & filter, air filter & spark plugs.

Sinced the problem started I have checked the coil packs, changed the MAF sensor and the pre cat lambda sensor but still havnt cured it!

Any ideas?
Reply | Report as offensive | Link
Thu 24 Jun 2010 13:45
Audi A3 1.8T - Juddering, bad idle - 659FBE

How did you check the coil packs? The symptoms you describe could be attributable to minimal spark energy, giving intermittent ignition under worst case conditions.

659.

Reply | Report as offensive | Link
Thu 24 Jun 2010 13:52
Audi A3 1.8T - Juddering, bad idle - Nick Mazda 6 TS2
Firstly I bought a single coil pack (to save money) and tried it in each of the 4 cylinders with no joy. I then checked all the original packs by waiting until it started running rough when idleing and unplugged each coil pack in turn. When I did this there was no change, it still ticked over rough and occasinally misfired indicating that the coil packs aren't causing the problem.
Reply | Report as offensive | Link
Thu 24 Jun 2010 14:39
Audi A3 1.8T - Juddering, bad idle - Peter D

I suggest you stop fiddling before you damage soething. For starters you do not disconnect coil packs when powered as you run the risk of popping the drive amp or the ECU. Find a Vag specialist and let them sort it. Also post in appropriate section on www.VWAudiforum.co.uk

Regards Peter

Reply | Report as offensive | Link
Thu 24 Jun 2010 14:39
Audi A3 1.8T - Juddering, bad idle - barkas

I would try another pack of spark plugs as the prob started when you changed them. ...or....buy 1 new plug and take turns changing it across the cylinders to see if the prob stops....cheap enough...

Reply | Report as offensive | Link
Thu 24 Jun 2010 16:25
Audi A3 1.8T - Juddering, bad idle - Nick Mazda 6 TS2
I suppose I could try more plugs, the prob was there before I changed them though, it has just been worse lately. I cant afford the prices the VAG specialists charge otherwise I would take it there, They may not find the problem anyway as its so intermittant but they would still charge for trying so I may as well carry on with different things until I have exhausted all options. Cheers
Reply | Report as offensive | Link
Thu 24 Jun 2010 20:07
Audi A3 1.8T - Juddering, bad idle - Peter D

Well you have paid out for a MAF and O2 sensor that did not crack the problem. Whatr would yo like to through money at next. Regards Peter

Reply | Report as offensive | Link
Thu 24 Jun 2010 20:12
Audi A3 1.8T - Juddering, bad idle - Nick Mazda 6 TS2

An ignition amplifier module I think next, can get them cheaper trade. Im not paying the rip off prices a specialist charges unless I have to!

Reply | Report as offensive | Link
Thu 24 Jun 2010 21:46
Audi A3 1.8T - Juddering, bad idle - Avant

Answer fromn GS to same post in Motoring section:

Blocked injectors,fuel filter, faulty sensor? Try Wurth fuel cleaner.

I've closed the other thread - one is enough.

Reply | Report as offensive | Link
Fri 25 Jun 2010 19:28
Audi A3 1.8T - Juddering, bad idle - sandy56

It could be a host of things or just one.

Try taking it to a BOSCH independent garage, Get a price for an inspection/ check with the VW computer and see what that says and go from there.

Reply | Report as offensive | Link
Sat 3 Jul 2010 00:52
Audi A3 1.8T - Juddering, bad idle - ianjoh

You may have an air leak into the manifold, check the small vacuum hoses as these often disintegrate. Also it is worth cleaning the air temp sensor which is mounted just after the throttle control valve, it is fixed in with 2 screws and will come out fairly easy. It may be caked in soot from the egr valve just upstream, carb cleaner & toothbrush works well.

I got a significant improvement in behavior on my alhambra 1.8t after a clean, I also cleaned the throttle valve while I was at it, it is still not 100% so I have some more work to do eleswhere.

Reply | Report as offensive | Link

We give you the low down on how to save on insurance, little-known tricks and tips, what insurance groups mean and how to use insurance aggregators to beat insurers.

Insurance group finder and how to save on insurance