94Q stumbles when cold part throttle

[psychic_mechanic]

The title pretty much says everything, the car stumbles a bit under part throttle (at speeds 60-80 MPH) when not fully warmed up. At WOT or when warmed up it drives great.

The problem started out as intermittent, but is happening pretty much all the time now.

Is there something I should look for as a cause?

[Q45tech]

Why are you driving at 60-80 mph with cold oil and cold coolant.

It only take 5 minutes Summer; 10 minutes winter to achieve correct operating temperature........unless the thermostat doesn't get changed every 3 years.