Well... It sounds like there are several problems, as I can't think of one cause for so many different symptoms. I agree with (CZ)enda's idea of the cam timing as a possible explanation. But I think you need to try and eliminate the problems one by one, and hope that the other problems go away as well.
Chas voiced my thoughts on the airbox clip. While you've got the airbox off, clean the pipe from the camshaft cover (the short black pipe ~2cm diameter) as if this breather is blocked, that may in theory cause your blue smoke issue. More on that later...
OK, the first thing I would sort out would be that screeching noise. In your first post, you referred to a burning-plastic smell. That immediately made me think 'alternator'. The alternator comes under most load directly after starting the engine. If the alternator is faulty, or there is a short in the wire from it, the load may be so high that the belt is slipping (screeching). Or, the belt may be in poor condition anyway, and may slip even under the normal high load after engine start-up.
The only thing is, this does not tally with the noise being connected to the use of the clutch. But, fixing the alternator or its belt is much easier than fixing the clutch, so I think you should eliminate the alternator as a cause first. Loosen the two 17mm-head nuts, use an extension bar and a ratchet handle from behind the brake master cylinder. Remove the belt. On the FIRE engine (which your Uno has) the belt drives only the alternator, so it's safe to start and run the engine (the battery-light will be on, because the alternator is not charging). Maybe go for a drive, listen and smell for any improvement.
Inspect the belt, particularly looking for cracks on the inside surface. If it looks glazed (it probably will) then replace it - cheap enough (5-10 pounds, maybe less).
Next we must ask: has the rough idling/stalling been an ongoing problem, or has this suddenly appeared with the smoke/noise?
If ongoing, you need to suspect the usual culprit - vacuum advance unit on distributor or its vacuum pipe, blah blah
I'm always writing about this one! Pull the pipe off the injection throttle body (trace the pipe from the distributor), clean the end, and suck on it (yes really) - if you can draw air through it, the diaphragm probably has a split, if there is a feeling of mechanical movement and no airflow, then that's good. Having fixed this, you should probably get someone who knows about the SPi fuel injection to adjust the idle mixture/speed. Sorry, but I have experience only with the carburettor FIRE engine.
I remember with the injection model there is a switch on the throttle that must close when the engine is idling, otherwise the fuel injector puts in too much fuel and idling will be rough/stalling. So, you should check that the switch 'clicks' with the throttle closed (I think it has a black push-button) and use a multimeter (electrical tester), with the engine switched off and the two probes across the switch on the 'Ohms' range, to check that the switch really is closing.
If the problems have had a sudden onset, then perhaps it is more likely to relate to the cam timing, as (CZ)enda suggests. Remove the cambelt cover (simple - 10mm bolts, don't forget the slightly hidden one at the bottom rear edge). Turn the engine until the TDC mark lines up - I use the ones at the flywheel - there's a window on top of the gearbox bellhousing, get a torch (flashlight) and with the car in 4th gear, push forward until the notch in the flywheel lines up with the '0' marking on the bellhousing. Then look at the camshaft pulley (exposed once the cambelt cover is off) and imagine it's a clock face. At about 42 minutes to the hour, there should be a fine notch in the pulley and a wide, shallow notch in the aluminium of the cylinder head. If the pulley is 180-degrees off, turn the engine one complete turn and re-check (the camshaft turns at half engine speed).
I think you should check the cambelt tension (you should be able to twist the belt through 90 degrees on its longest run). To reduce whining noises, I tend to go for slightly less tension than this... maybe allowing the belt to turn through 120 degrees - if in doubt, get the opinion of someone who has changed several cambelts before
Perhaps at this point, run the engine with the belt cover removed, noting any strange noises from the tensioner bearing or slackness visible in the belt.
Hopefully by now you will have found the cause of the noise... if not (and if it is still related to clutch in/out) then that leaves the clutch release bearing or gearbox noises. The input shaft bearing in the gearbox has been known to fail, but that will usually have given a roaring noise when moving off in low gears - often for many thousands of miles. I also wonder if the oil level being low/nonexistent may give rise to strange noises with the engine idling. Do the gears select normally when driving? Have you checked the oil level (12mm hex plug on front of gearbox, should be full-to-overflowing with ZC90 non-EP oil). If yes and yes, we can eliminate the gearbox. Changing the clutch release bearing is a time-consuming job, but the part is relatively cheap (you'd probably want to change the clutch as well). Perhaps leave your decision until the final chapter (below)...
...because that still leaves us with the knocks and the smoke. As PeterG says, it could easily be a blown head gasket (though I disagree that the Uno is reknown for blown head gaskets
I suspect it may be down to the lack of maintenance that an average Uno in the UK might get). You need to keep checking the engine oil for signs of water (cream) and the coolant for signs of oil. The coolant should be green, incidentally. Are you having to top up the oil or the coolant? The engine oil should only need topping up once every six months (say) or maybe once every three months for heavy motorway use. The coolant should stay above the 'MIN' marking for at least a month, probably two months. If you're having to top up every week - or every couple of days, or several times a journey - that is a sign that the head gasket is blown. If slightly blown, maybe one or more cylinders are filling with water after engine switch-off. But you would notice this as the engine firing on three (or two!) cylinders. Does it start smoothly on all four?
Personally I don't suspect the head gasket. I think you have either the oil leak that Chas mentioned, or (I hate to say this) maybe you have the first truly worn-out FIRE engine that I know
The FIRE is NOT known for worn out piston rings/bores, but that would explain your knocking noise at idle (piston slap) and the blue smoke. There would also be a high oil consumption of perhaps one litre/1200 miles.
You may like to do a compression test (gizmo that pushes into spark plug hole and measures pressure with the engine cranking over, throttle open) or have a mechanic that you trust do this test for you. From memory, the pressure should be 160-170ish psi. If all cylinders are evenly less than this, the rings/bores are probably worn. You can squirt some oil in and re-test (if worn, there would be noticeable improvement) to confirm this.
If this is the case, I think you should swap the engine for one from a breakers. This much wear would be unusual (even in engines with over 150,000miles), so it is not worth spending the money to rebuild an engine that is quite commonly available. Incidentally, worn rings/bores and low compression would explain the lack of 'pep' that you mentioned.
If only one cylinder has low compression, you might have a broken piston ring, or it's still possible that the head gasket has blown. I find that if only one cylinder is low, the engine tends to make a distinctive 'stirring' sound when cranking over, as it cranks over faster for 1/4 of the time - you can hear the speed fluctuating. You would probably want to remove the head at this point for a diagnosis of the gasket.
Noises are very hard to diagnose from a description - you really need the opinion of someone in person who is familiar with these engines. I mentioned the piston slap before - by itself, not a cause for concern, but if accompanied by the high oil consumption and blue smoke, it's not a good sign. May result from drastic overheating in the engine's life. Another common (and inconsequential) noise from the FIRE is a tick-tock-tick-tock noise that disappears above idling speed. It is said to be caused by the connecting rod little-end bearings in the pistons. A change of oil may reduce the noise, but if not it doesn't matter.
Most FIAT gearboxes rattle in neutral with the engine idling, sometimes but not always because the gearbox oil level is low. Does the rattle stop when you push in the clutch? If so, and the gearbox oil level is correct, then this is also nothing to worry about.
Clicking from suspension - is this really more of a clonking? Can you feel it in the steering? If not, probably nothing to worry about. Spray the base of the suspension spring with WD-40 if it really is a clicking noise, as the end of the spring may be catching or sticking. If 'clonking', suspension bottom balljoint is the prime suspect as Chas says. I'd leave this problem for now, at least until you get the above issues sorted. Jack up the right-front wheel and try to shake it in several directions - satisfy yourself that there is nothing loose (strut bolts/steering tie-rod end/wheel bolts/wheel bearing). Usual disclaimer here: by telling you to ignore it, I can't be held responsible for damage/injury/death that results from some imminent failure! So if in doubt, get the opinion of someone experienced who can check the car in person...
Well that's an hour from me, now over to you - hope your process of elimination is successful...
-Alex
