dvarholy

The 931 is interference. The non-turbo 924 is not. The "belt tool" like used on the 924S/928/944/968 is not needed to change the belt. The belt itself is the same for either. The 931 valves are unique and NLA. Always rotate the engine by hand first to be sure no mistake was made in timing.

Daniel

'86 951
'82 931 (long gone)

fasteddie313

OMG look at that timing belt!
Put a new timing belt on it ASAP #1 priority before you ever crank the engine over again! Or you may ruin your engine.
It's like $20 including the tensioner..

Then you should pull the distributor cap and check the contacts. Pull the plugs and check for spark on all 4. Post pic of plugs.

Your video looks like a massive air leak somewhere between the head and AFM.
See all of those small vacuum lines that look like braided cloth? Replace all of them..
Go under the car and check out the rubber boot that goes from the turbo to the bottom of the Air Flow Meter AFM. Check for cracks or tears.
While you are down there their is a smaller rubber 90 degree coupler from the turbo to a metal pipe behind the timing belt. Check that for cracks/leaks.. The other end of it is under the intake you can check if you swing the alternator out of the way.
Around your intake manifold, check all of the hoses/connectors for cracks and leaks. Check the one that goes around the intake from the upper charge tube around down by the oil dipstick and back to the backside of the intake..
Just inspect/replace all possible vacuum leaks anywhere between the AFM and head.

Then..
Pull your valve cover and check out your cam. Get some feeler gauges and the haynes manual and adjust your valve lash.
Check that plastic 90 under there that goes from the head to the cam oiler tube because they break commonly.
The least you could do is look under the oil cap on the valve cover while it is running to see if the oiler tube is working..

Then you can try starting it again (not before a timing belt) unless you want to jump right into an injector flow test and/or CIS pressure test.
Check out that Haynes for the injector flow test..
Something like this video, skip to like 1:30.

Gain access to that AFM, pull your injectors and put them in bottles back on the lines, Jump fuel pump pins 30-87 for fuel pressure, Spray them a lot and see if they fill the bottles evenly, see if they spray nice cone patterns, see if they even all spray at all, etc...
You will eventually have to buy or make a CIS pressure tester to know everything is right.. Search "CIS test kit" even if your injector flow test looks good..

When you get it running again their should be something buzzing under your throttle body. Is it buzzing?
Start it with the cap off of the coolant tank and see if you see bubbles in there to check for a blown HG.

I guess that's all for now.
How deep do you want to go with this car? Their is going to be a LOT of stuff to make sure is right and you likely have multiple running issues but atleast you are running to start with!

I happen to have a complete known good working CIS system that fits your car and I might part with some or all of it if you need a piece and are serious about fixing up this car..

That is a Badass car that you have there with the m471 sport suspension package (5 lug), and the best option wheels, and likely a limited slip rear diff that is rare and valuable.
Armrest, great exterior color....
Awesome car. Best of all the 924s IMO. Rare lucky find.
Is it a 79 or 80?

What are your plans with this car? Are you serious about fixing it up? Have a couple hundred hours and $ to spare to make it right?

Ah I see it's an 80.. These are great links to start with..
I can't believe nobody has screamed TIMING BELT @ you yet..

Whatever smoke you are getting isn't that bad and I wouldn't be that overly worried about it just yet..
Timing belt-vacuum leaks-check spark-start it-check under oil cap for top end oil-check coolant for bubbles..

What do you want to do first after you replace the timing belt?
Well I suppose you could do an injector flow test, CIS pressure test, and look extremely thoroughly for vacuum leaks. But don't run that thing with that ancient timing belt!

https://www.ebay.com/itm/For-Porsche-924-1977-1982-Timing-Belt-Contitech-056-109-119-A/350776507454?epid=1229652642&hash=item51abe8bc3e:g:FZoAAOxyuCJRdUIa
$10 timing belt

https://www.ebay.com/itm/Timing-Belt-Tensioner-Roller-Audi-80-90-Porsche-924-VW-Golf-Jetta-026-109-243-L/290641709989?fits=Model%3A924%7CMake%3APorsche&epid=1160434375&hash=item 43ab988ba5:g:MCIAAOxyQj9ROxQQ:sc:USPSFirstClass!49659!US!-1&frcectupt=true
$8 tensioner

The hardest part, throwing away the timing belt guard/cover, is already done..

Watch this awesome video..

Dwizle

Owned one of these in the past sound like you have a strong fuel system.
Have you checked the Valves for adjustment they have a screw type adjuster
and they might be adjusted too tight that when the engine heats up the valves are no longer sealing
so you can't maintain compression did you do your compression test when the engine was hot or cold?
do it a gain but this time hot n cold see if there is a difference also there is a large rubber O-ring on the outlet
side of the compressor that likes to roll down when you slide the lower intake tube onto it that might be the source
of your vacuum leak.