88 760 turbo intermittent spark

This is starting to drive me nuts!

10,000 miles on rebuilt engine (B230FT), been running perfect. Suddenly
developed rough running. No smoke. Replaced distributor (found leaking
inner seal anyway, so needed that whether it was the problem or not) with a
new one. New plugs.

Connecting a timing light to any plug wire, or the wire from dist. to coil,
or "+" wire on low side of coil shows that at random points, there just
isn't a signal to spark. Tried two different ignition modules (located on
inner driver fender) with no change. Tried disconnecting knock sensor, no
change.

Thoughts?

TIA,
Tony

 

check throttle positioning switch cable mine slipped off!

 

Checked... no obvious problems. Clicks when it's supposed to...

More info:

rough running is as if someone's killed the key for a split second, then
turns it back on... very electrical in nature. Happens most when engine's
cold.

Also, under heavy acceleration and boost, right around 2500-3000 rpm
develops 'popping' noise similar to backfire, but doesn't seem to come from
exhaust.

Once engine reaches normal operating temp, these problems fade greatly or
disappear completely. Beginning to think that a temp sensor is going.
Pulling the wire from the ECU temp sensor kills the car and will barely
start, which I believe is normal, since the computer sees that as infinite
cold and dumps in the gas.

Have ordered new temp sensor, fuel regulator and O2 sensor. Not that much
$$, and it'll eliminate those items. (should've done that anyway when I
rebuilt the engine)

Thanks!
Tony