[ossiblue]

I'm thinking along the same lines as Tony, your warm pressure is too low which may be causing an overly rich warm start condition. Usually, the warm pressure is ~3.2 bars (not exactly sure for a 79, but it is not 2.8, that's for certain.) Typically, symptoms like yours point to a loss of residual pressure, but your numbers appear to be good, assuming they were taken with the valve open. If your heating element is bad, the wur has to warm through the ambient heat of the engine, so you need to be certain the pressure you measured was for a fully warmed bimetallic arm and the pressure is as high as it will possibly go.