1985 T16s - running rough, revs dropping, stalling
It appears to be time for my three-yearly visit here. This time, I have more symptoms than I know what to do with, but can't narrow it down to a single culprit. Any suggestions on diagnosis or what's most likely would be very welcome.
A few months ago, I had issues with stalling coming up to a particular junction - slowing from 30 (mph) to 20 and changing down to second. It happened once or twice, then I had a stallathon where slowing for any lights would trigger it. Swapped in a used but good turbo dump valve and a new line for it, and everything seemed ok. Then, it had a couple of stalls at the same spot, and I mentally made a note to look over the dump valve again.
Cut to a week or two later, and the Saab was on its first trip of over 5 miles for a while - on the way back, it started sounding slightly rough - just skipping the odd beat. 20-odd miles later, the idle revs were falling off, and it started stalling with the same dump valve-type behaviour. It was also running rough, though, so not exactly the same. Pushed on a little further, and it would stall at idle, and I had to keep the revs up to keep going. A short while later, the revs stopped staying stable at higher revs - rev it to 2000, keep constant throttle, and it would drop to 1000. At that point I pulled over somewhere safe - it wasn't going to make it home.
Since then, I've had the bonnet up, checked that the vacuum hoses were ok (cut back and refitted a couple of so-so ends), and that the turbo dump valve was holding pressure. Also changed the spark leads, one of which I think got snapped at the plug end by an enthusiastic recovery guy. Symptoms are - starts, runs rough then dies. If I put the revs up, it will rev, then suddenly change its mind (after a second or two) and drop to rougher running at lower revs. I'm also hearing a turbo-like howl I'm not used to. It could just be that I have the bonnet open and the door open, so I can hear the engine a lot better, but I thought I'd throw it in there.
It's also now reluctant to start a second time - i.e. I can fire it up in the morning, go through the cycle above, and then try to restart it 15 minutes later after poking around the engine bay, and it'll turn over, catch occasionally, but not start. No signs of fluid leaking anywhere.
Any thoughts?