Violent shaking...help out a noob?

[natey]

Can anybody help me out?

First, let me say that I don't have much experience with the wrench. But I'm tired of taking my car in for stuff that seems minor, and I'd like to avoid it if possible. On with the story...

'89 944 Turbo. Bought over the summer, great condition, ran perfectly. December 20, I took it out for some exercise, got it good and warmed up, then parked it until Jan. 15 or so. Around then, I took it in to have my wheels/tires looked at (4 bent wheels, dontcha just love ebay?). I drove it about 3 miles, it sat outside in 40 degrees+rain overnight, I drove it 3 miles home, and parked it for ~5 days. It was running well.

The weather goes below 20 degrees (car is under carport, outside). Weekend comes, I start it up for some more 'exercise'. The car starts easily, and runs normally for about five seconds. Then it begins shaking, violently. I don't remember any particular noise when it started. Idle speed dropped a bit, engine stumbled slightly. Wondering if it's transitory, I gently rev it to 1500 rpm. It feels like riding a mechanical bull.

I shut the car off. I waited 30 seconds. I started it again. (It's a software engineer thing...push it back up the hill and try again...reboot...sorry.) Same shaking. Shut it off, haven't touched it since.

From searching the boards here, it could be anything from bad gas to a timing belt (or balance shaft belt) problem. I don't think it's the motor mounts, as it started so suddenly. I know the timing belt hasn't broken outright, as the engine still runs.

I'd be willing to believe something fuel-related...5 seconds seems about right for something to get from the gas tank into the engine. But it ran fine less than a week before, and I'm guessing gas goes bad over a period of time, months?

So, I'm wondering what to do. Basically, I think my options are:
1. Run it and see if it gets better.
2. Drive/limp it to the mechanics, 3 miles.
3. Tow it to the mechanics.

What are your recommendations, and are there some simple things I can test to narrow it down? Thanks...

[Dantilla]

If it was the timing belt, the car would not run at all.

My first thought is a balance shaft belt, but I have no idea how much vibration there is of it goes. Some race engines go without the balance shafts at all to save weight and last quite a while. I wonder if one of your shafts jumped a tooth or two and is compounding the engine's vibrations.

[bluebullet]

If the balance shaft belt would have broke the vibration would be harsh, but not as harsh as if it skipped a tooth or two (now instead of just not moving and the motor vibrating, its now two heavy shafts that arent spinning in tune with the motor and it creates a lot more vibration).

Cold weather wreaks havoc on belts, and they become dry rotted or cracked, specially if they havent been changed in some time. Id have it towed to your shop, because if in fact the balance belt didnt break, you dont want it getting wedged into the timing belt at the bottom and taking that out too. You'll be looking for a new motor if that happens. If you can pull the middle cover off the front of the motor (i think its like 7-8 10mm bolts?) you can take a peek inside and see what both belts are like.

Race motors built without balance shafts have the whole rotating assembly balanced to a greater degree than the factory does. This helps keep vibrations down because the parts are all within a smaller tolerance of each other. Instead of balancing it out to say 1gram or so, a race motor would be balanced til .5 or even if you could, .0X. The guy we use that does our turbos balances them til the scale bottoms out (it will read 0.000 across, unlike Turbonetics which balances them to .3)

[Brando]

After you inspect the belts for damage, if they look fine in all respects, try starting the car and letting it run until it reaches operating temp (end of the white square or first bar on your temp gauge). Does it continue to run poorly?