cliffcoggin

It would be a heck of a co-incidence if the airbag sensor failed just when you removed the door panel. It's more likely I suggest that you have dislodged a plug connector or broken a wire.

It's common in such situations for pins to be plated, sometimes even with gold, to resist corrosion. Once the plating is removed corrosion can return much faster, though a few weeks seems unusually rapid in this case. Are you sure water isn't getting in or condensing there?

Thanks for the update. That was remarkably cheap for Audi. Kudos to them. Very odd about the manual cable. I assumed its function was an alternate opening method in case of solenoid failure.

Mad. Your problem is simple: the clutch is clapped out. If you don't change it soon, your gearbox will be too.

In hindsight I didn't phrase my reply very clearly, so as Gareth said test for looseness with the wheel bolted on and let us know the outcome. Do the test with the wheel off the ground, rocking it left & right and top & bottom. Listen and feel for any movement as well as looking, your ears and hands can give valuable information.

Rob. Even if the single screw that holds the disc in place is loose, the wheel studs provide the main securing force, so the main question is whether the disc is moving independently of the hub or is the hub moving with the disc. If the hub is moving with the disc then the bearing is worn or loose.

Fair enough Gareth. It's been forty years since I used a sealant like that, and I have no doubt technology has moved on since then.

As a short term measure until you get a new radiator plain water is perfectly fine and will do not the slightest harm to your cooling system. The coloured coolant you refer to is a mixture of water, anti-freeze (ethylene glycol), dye, and a corrosion inhibitor. The anti-freeze component is in it for obvious reasons; the corrosion inhibitor is essential for long term use to prevent the electrolytic corrosion which occurs between the different metals in the cooling system, (aluminium, copper, steel, zinc.) Whether the repair will survive a 400 mile round trip is unknown. It really depends what sort of sealant was used, how big the hole was, and whether that part of the radiator is under enough stress to open up the repair. What concerns me equally is the thought of all that sealant circulating round the cooling system. I don't know if modern sealants are any better, but at one time there was a fear of it clogging up the narrower water passages in the system. In your position I would certainly not trust the car for anything more than a few miles at a time on non-essential journeys. Get the train instead.

It's remarkable how little corrosion is needed to spoil the operation of some electronic systems, and how much effort is needed to overcome it. I admire your perseverance David.

I reckon you have the culprit in the suspension changes, Maris. Naturally you'll have to put the springs the right way round and then get the toe-in (tracking) reset, but I'm not sure if that will be enough to stop the tyre wear. By that I mean that I don't know if spring changes also need track rods etc. to be different. That's a point you need more knowledgeable advice about than I can give.

Maris. To wear the shoulder of the tyre like that either the suspension geometry is wrong or the tyre is rubbing on the wheel arch. I would get the tracking tested again as a first step. If that proves to be OK look for slack in other suspension joints. PS. Do you have wheel stud extensions or non-standard wheels?

I give up. Without specific and exact explanation of the techniques you have tried I can be of no further assistance, so I am withdrawing from the discussion. Good luck in solving the problem.

Tom. What, if anything, have you actually attempted to resolve the problem in practical terms? None of us can advise appropriately unless you tell us what you have done and what has failed.

DuckDuckGo revealed many suggestions: https://www.audi-sport.net/xf/threads/how-do-you-bleed-the-air-out-of-the-cooling-system.87168/ https://www.fixya.com/cars/t1866067-bleed_coolant_system_audi_a3 http://audifans.net/ftopicp-88989.html http://forums.tdiclub.com/showthread.php?t=127037

Do let us know the outcome of the kit if you get one. It appears to be a common problem so it would be good to know of a home fit solution.

I've not heard of the repair kits. On the face of it they seem like a good idea having multi-strand wires and silicone insulation for flexibility, however the quality of manufacture is going to be critical, and that's something you can not assess in advance. Perhaps buy one for testing before committing to more.

Every engine generates some pressure in the crankcase which is normally taken care of by the EGR, (exhaust gas recirculation,). However if the piston rings are worn there will be a lot of crankcase pressure that needs to go somewhere. I speculated, and it was only speculation, that the plug was to stop that pressure blowing up the dipstick tube. When you mention the manifold I assume you mean the exhaust manifold not the inlet manifold. By bubbles do you mean soap bubbles for testing or something else? If your mate is as knowledgeable as you suggest he can explain the detail. Ask him if the EGR has been blanked off.

The suspicious side of wonders if plugging the dip stick hole is to hide excessive crankcase venting. The more benevolent side wonders if it was to stop water getting in while jet washing the engine.

Sorry, missed that.

Look in the boot for a plastic cord, (I believe it is orange,) behind the lining fabric which you pull to release the fuel cap.

Pity you didn't mention the new header tank earlier. To change that tank the cooling system must be partly drained, which will introduce air into the system. If I was a betting man I'd put money on your cooling system needing to have air bled out of it. Nevertheless Steve's suggestion should not be ignored as it is a much easier problem to fix first.

You may have an air lock in the heater. Try turning the temperature up to maximum for a few minutes once the engine is hot and run it at moderate speed. If any air is shifted you should see the level drop in the header tank. Do you know where the leak is from?

At that mileage the engine should be OK unless it's been thrashed by a previous owner, which is a possibility given that EGR and DPF have been disabled. It's hard to tell from just a one second sound clip but it sounds like the rattle is from the top end of the engine, rather than big ends or main bearings.

One other question. Is it using a lot of oil?

What's the mileage of the engine and do you have service history?