86 5kcsq still stumbling when cold

[Stacy]

I have sold my 86 5kcsq. The new owner is still having the same issue that I
had with it, that I posted here previously about. 

 

A quick refresher:

 

Car starts fine, after about 30-45 seconds, the car will stumble and
sometimes (usually) backfires slightly when taking off, it smoothes out once
the car is moving and above about 2k rpms, once the car reaches about 80% of
warmed up (which on this car, is the about 3mm to the left of center of the
temp gauge) the problem pretty much goes away. 

 

What has been checked so far...

 

Replaced crank case breather, replaced warm up regulator with a known good
used one, checked for vaccum leaks at all the normal places on the MC1 (
hoses at back of intake, between intake and head, turbo boots etc), new
plugs, new airfilter, car runs fine otherwise, makes good boost, climate
control works (sometimes a sign of a vac leak in that system)  Ran some
magic mystery oil through the crankcase on the odd chance there was some
sludging somewhere, no change.

 

 

Any suggestions or ideas would be greatly appreciated.

 

Thanks!!

 

Stacy