I'm a statistic!
I've got this problem too... noticed a weird shuddering when I went to pull away last Sunday, and thought I was in the wrong gear, so I took it out of gear and went back into first, and the same thing happened, plus the engine light flashed on and off... After a little while it stopped, so I continued on my way home.
Monday, I went to work (about 20 miles away in Slough), and had the flashing light on the way in, so I called my brother (he's a manager at a Halfords Autocentre), and he said he'd being home the diagnostic computer to take the readings with. On my way home, the light came on permanently, and I started getting bombarded with "pings" and "Have engine checked" messages.
So my brother hooked the computer up, and got messages about a misfire on cylinder 4. Having read this thread, that was pretty much what I was expecting, so I called the garage at 10am on Friday (when they were first open after the new year), and took it down to them.
They plugged their computer in, and got the same error, so swapped a coilpack over from 4 to 5, to see if it was that or the sparkplugs or whatever, and the error moved with the coilpack. Easy diagnosis, they said they'd order another one, and I should come back on Monday to get it installed.
So I went off home at around 12, got about 5 miles away, and the car felt awful, much much worse than it was before, and when I stopped in traffic, I saw smoke or steam or something coming out of the bonnet, so I pulled into a layby and turned the engine off...
I phoned the garage, and they said to open the bonnet and check to see if I could see where the smoke was coming from. So I tried that, couldn't see it, but it definitely smelled of electrical burning. I called them back and they said to bring it straight back to them, and they'd sort out a loan car. Which was great, until I couldn't start the engine again...
So they sent a guy out to look at it, and he swapped over the bad coilpack with a used one they had, but still nothing. So I had to call the RAC (13:30). Who told me that there would be a 2-3 hour wait...
The RAC turned up after an hour (14:36), which was pretty good going, and the guy had a look under the bonnet, agreed with the smell of electrical burning, and said there pretty much wasn't anything he could do. Not even tow me to the garage, because I've got the Q4... so I'd have to wait for a flatbed truck to pick me up.
The truck arrived at 17:00, by which time I was completely frozen, hadn't had anything to eat or drink since the cup of tea the garage gave me at 11am, and had finished a 600 page book I'd brought with me...
So the upshot is that my car is at the garage for the foreseeable future, they'll take a look at it on Monday and try to work out what's wrong...
The only upside to this is that I only bought the car in May 2013, so I'm still under their 2 year warranty!
1984 Ford Capri 1.6 Laser (1998-1999)
1983 Ford Capri 2.8 Injection (1999-2003)
2002 Vauxhall Omega 2.6 CD V6 (2003-2013)
2008 Alfa 159 3.2 Q4 Lusso (2013- )