Slight misfire after timing belt replacement?
 

Hi all. Picked my new 1999 S8 up a few weeks ago and I'm really impressed with it. It's done a few miles and I was expecting it to have a few knock, rattles etc - but nothing. I bought it on the pretence that it needed a timing belt replacing within a few thousand miles or so.

I got it in to my local garage for the belt, pullies and water pump to be replaced. Picked it up on friday and it seems to have a slight misfire/wobble on idle. I'll be getting it back in to the garage next week but just wanted to see if anyone has had a similar experience or know what it might be as they are not an Audi specilist.

Thanks in advance.

Hi tonyt102,

Welcome to the premier A/S 8 forum and the joy of owning what is a lotta mota for your £.

Ben of AV Performance may be around shortly but I can guess what he may say.

As they weren't a Audi specialist it is unlikely they had the specialist tools for doing a cam belt change. It can be done without them but the chances of error are significantly higher. I would suspect that there is some misalignment in there somewhere which is manifesting itself as a lumpy idle.

Do you have VagCom or does your garage? Check out the error codes.

I see you are up in Cleveland. There may be a forum member that will do a VagCom scan for you nearby.

Read up on the fanbelt change here . Being a 99 it could be a 32 Valve or a 40 Valve. procedure for a 40 valve is different.

Hope you get it sorted.

Check out the A8oc and maube we will see you at one of the events.

Also if you need bits then the forum sponsors are the best suppliers in the UK. A8 Parts.

Thanks for the reply.

I do have the free version of VAG COM so I'll have a look when I get the lead back from my brother. The garage has a Snap On reader so I guess that that should show up any errors.

As for the use of the specialist tools, I'm not sure but I'll ask them about it.

BTW, it is the 40v version.

I'm sure I'll get it sorted.

Cheers.

I haven't used my VAG-COM since I've had my computer with Vista on and it looks like the free version isn't compatable. It's in at the garage tomorrow so we'll have to see. I think I may invest in the proper cable and software.

Well, the garages Snap On code reader didn't bring anything up. They say that many of the vac pipes are perished so I've asked them to thoroughly check/replace them as necessary although I'm not convinced that this is the issue.

Does anyone know if there are timing marks that everything should match up with behind the covers? I asked them today and apparently, they do have the specific timing belt replacement tools.

It's a good call. Leaking breather hoses can effect the idle and they do perish. You can replace the front one with a length of 3/4" radiator hose. the Audi original is 20 to 30 squid. the ones at the back are a bugger to get to and are about £70 the pair.

Yeh, I agree that the breather pipes couple casue idle problems but it's strange that this should occur right after the timing belt change. I can imagine that the vac pipes can become damaged from removal/refitting but I'm not sure about the breather pipes. I really don't know as I've never seen the front end of these engines and I don't know what's disconnected when the belt is replaced. I'm just really worried that the indy I have it at can't sort it and I have to get it to a specialist, doubling the money I've spent.

Thanks for the replies Conan.

Well, had all of the vacuum hoses replaced to no avail.

I have plugged VAG COM in tonight and it brought up no fault codes. I'm quite new to VAG COM so correct me if I'm wrong. I went to the measuring block section with the engine running to get some values for misfiring cylnders and ignition timing. There was no misfires logged although the timing showed between 12-14 degrees BTDC @ 800rpm - is this right as I can find out what it should be? Shouldn't it be 0 degrees or near?

When you say vacuum hoses do you mean crank case breather hoses?

Vacuum hoses effect the variable length intake adjustment.

If your running Vagcom and measuring Blocks 1 , 19 and 20. If you have ant misfires blocks 19 and 20 will record each misfire as it happens. If they stay at zero then no misfires are happening....... I think........ :)

Use the Vag scope facility and record blocks 1 , 19, 20 and post the file as an attachment here. Rev up to about 4k.