I personally wouldn't touch part worns unless you know for sure where they came from.
I used to buy them when I was younger to save money, but it turned out to be false economy and alot of them had invisible faults, hence why they were removed in the first place.
some examples are
I had a full set which looked perfect, but when they were on the car it shook terribly, when I went back to the seller it turned outthe car had been torched but the tyres were ok, on further inspection it turned out they were all warped due to the heat.
Others I have had, had bulges which weren't shown until the cars weight was on them, but if this was on the inside of the tyre it wasn't seen unless I get under the car without lifting it off its wheels
I also put on tyres that had slightly more wear to one side than the other due to previous cars misalignment, they also wore down very quickly
When I did more research I found out once the tyres have worn unevenly, even though you might get tracking or whatever is causing the problem corrected, the tyres will not correct their wear and stay in the already uneven worn shape so still wear unevenly.
Well my EGR must be mechanical as there are no electrical wires going to it. Simply a small pipe attactching to the top (which is the vaccuum pipe I plugged)
My mistake in describing the egr
There are three egrs on the mk3
A vacuum powered one (euro3) which it sound like you have. This just has the hose and no electrics. The EML almost never comes on on euro3s.
A vacuum powered one but also with an electrical connection (euro4) this works the same as the previous one but when you blank the egr or block up the hose the EML more likely than not comes on.
The mechanical one (also euro4) where there is no vacuum hose as all and its just an electric motor that opens and closes the valve.
If you only get smoke when you really boot it, this could be normal. Excessive smoke often means an egr problem of split air hose, as James says the hose just before the egr is the usual one to split but the others have sometimes been known to.
If there comes a point where you think a hose is split, a visual check doesn't always show the splits. The best way to check is to remove them and give them a bit of a twist which will open up any splits.
Silicone hoses can be bought on ebay for less than half the price of fords rubber ones and will last alot longer too.