[:'(]

1987 Audi 4000CS Quattro

This has been killing me for the past couple of weeks.

My engine will randomly just shut off and the rpms decrease with engine speed.

Sometimes it'll turn back on, sometimes it won't, lately it doesn't turn back on.

Then I try to restart the car but it won't turn over all the way.

I have to wait, usually, 5 minutes before trying again and it'll start back up.

Sometimes I have a rough time starting my car if I don't hold the key in ignition position long enough, then I have to wait 5 minutes before I can retry again and it'll start up.
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I've replaced the distributor cap and rotor.
I've inspected the spark plugs wires and spark plugs and both seem fine.
I've checked the hall sender wires and connection, looks good.
I've checked the three grounds (left of intake manifold, and both behind and front of the valve cover) and they're good now.

Anything else to check now? I've tried Audiworld forums but I've seem to of hit a dead end.
Here's the link to the thread if you wanna read.

http://forums.audiworld.com/4000/msgs/130579.phtml