88 300TE hot misfire help needed.

[Merkey]

My sons 1988 300TE has a misfire, but only when really hot.
Once the car is moving and above 2000 rpm, I cant feel it... but it maybe there. It only seems to happen at 85/90C reading on the gauge... and only afer that temp is sustained for a while.

Changed the OVP and that cured a stalling issue.
Changed the sparkplugs yesterday, leads, rotor and cap are all recent.
Duty cycle I have varied from about 50% to about 75% without change.
Plan to replace all of the intake vacum hoses soon, and Fuel filter.

Couple of questions....
This car does not have an Air Temp sensor on the intake hose... there is a hole for it but no sensor... is that right?
It also only has one fuel pump, that I can see, There is supposed to be a fuel cooler inline. I read that there was an issue with fuel vaporisation in the line near the engine, that uses the A/C line to cool, but the A/C is not working, at this time.
I also read that the that the twin pump setup was added and cured this.
Anyone have any ideas?