Won't start when engine cold, first thing in the morning. new Idle Microswitch XJ6 4.2 1985, 135k miles.

We recently installed a new Idle Microswitch on my XJ6 4.2 1985, 135k miles. And we confirmed that it is making contact with an ohmmeter.

It does fire up but sounds like it is going to die.
then when I press the pedal the rpms go up, and it runs rough.
But when I let off the gas it dies completely.
Can someone suggest what to look into, or how to readjust the mixture settings with the Idle Microswitch in the circuit?

If I take the lead off the Idle Microswitch it runs smooth, and can drive around.
Then if I put the Idle Microswitch lead back on, it will start ok hot.
Problem occurs only when engine is cold, first thing in the morning.

The car was running fine prior to replacing the Idle Microswitch.
Everything has been replaced on the temp rail and new fuel regulator.

Thx in advance.
BrightonRay

 

Maybe your microswitch isn't set right? Who makes it?