Cold Start Question?

[Russ Southerlin <russell.s.southerlin@lmco.com>]

Have had some difficult cold starting problems lately and thought I
would see if anyone has any suggestions. Here are the symptoms.
Subject: 87 5KTQ
It fires on the second crank but stumbles and idles at a real low rpm
and will die. After another 2 to 5 tries it will eventually fire up and
idle perfectly.

It only does this on cold start.  The colder it is the BETTER it
starts.  If it is say 30-40 degF it will stumble but the other day it
was 12 DegF and started up much better.

I think cold start valve is O.K although it has been a few months since
I have chacked it.

Hot starts are good no matter how long it hot soaks.

I had a old used (but good) warm up reg. and replaced it and did not
notice any change.

I have checked all fuel pressures and they are O.K.

I have pulled fault codes and found nothing. Although I was getting a
rpm sensor fault a couple months ago. I think if there is no rpm signal
you would not get it to start at all.

Any Ideas?
Russ
87 5KTQ
Littleton, CO