300TE M103 rough idle when pointed down hill.
 

Hi guys i hope you can help. I pulled out my O2 sensor yesterday and gave it a good clean. It appears to have helped as my idle is much more consistent on level ground. The weird thing is when i stopped at traffic lights on a slope the idle was really rough but fine again on the flats. Any ideas what could cause this weird behaviour?

dirty strainer in the fuel tank at fuel outlet.

Great to have professional advise, much appriciated with odd faults like this.

mak