Rattle on acceleration, occasional exhaust pop.

[benk]

4-year old 1.8T, no chip, 62k miles.
Hi all,
Every now and then I get an exhaust pop, not bang, but loud enough to hear with windows down. Sounds like I ran over a short bit of plank or something.
Also, when sitting at lights, with car cold or hot, idle causes car to jerk enough to easily feel it through seat.
Thirdly, exhaust seems to rattle when accelerating - e.g. lots of gas in a high gear - sounds like a quiet rasping sound. Not harsh, but like the engine wants to do more but isn't for some reason.. hard to describe. It didn't do this
about 2000 miles ago.
Gambba posted a great ETKA image of the turbo (on a different forum site), saying I should check a gasket that could be loose, but I'm not familiar/comfortable enough to locate it and check.

Do these 3 symptoms combine to point to anything in particular? Bear in mind I'm at 62k miles and have not had timing belt done. I intend to do that pretty soon. In 3k miles or when water pump starts playing up. Whichever comes first. I'm thinking maybe jerky idle could be related to timing belt getting tired?
It's the exhaust rasp that's bugging me the most though. I don't get it when accelerating in a lower gear - only when starting to accelerate with a low engine speed. Could it be cat breaking up? I don't hear it when in neutral - revving engine in neutral sounds fine. It's a subtle sound, but annoying.

Any comments much appreciated.

 

[carlo]

I hada low down rattle from my exhaust when accelerating at low speed, sort of reaches a peak rattle and then rolls off (If you know what I mean).. had checked by Audi and they tightened exhaust heat shield, apparently water can get between as well and makes worse on damp days... This all sorted now... Also heard of same prob from guy at work who had turbo replaced and it mad no difference. They think it is a timing thingy, I can't remeber so will ask him and post again...

 

[benk]

Ok, I took the ignition control unit out and tested it with a 9V battery, some speaker wire and a digital multimeter. I got a good result for each of the four cylinders so I don't think that's my problem. (I used this info to do my testing: http://forums.audiworld.com/a4/msgs/1594531.phtml).

I still intend to swap the ignition unti (part: 4d0-905-351) with a friends' and see how the engine sounds.

I'm thinking now that problems may be caused by bad coolant sensor, causing engine to run rich, hence jerky idle and possible unburnt fuel causing exhaust pop. I intend to give exhaust a good clean and check for soot, and have also stuffed a tankful of Shell Optimax in, in the hope it will help flush crap out and may also improve ignition timing. That, combined with a new timing belt, tensioner (and water pump) should give me more info to go on, or even solve the problems alltogether.