Hi I have a 2010 Expert Tepee 2.0 hdi. It's quite smokey on start up take a good while to warm up but once warmed the smoke stops. I've noticed though while driving if say I'm holding the revs at 2000 rpm for example it's like the engine jump up and down 100 rpm and will do this every few second when being held at a constant speed. Although it doesn't seem to have this problem under acceleration or hard acceleration. Any help to what could be causing this. It has the fault code 1351 up but this is a glow plug issue so couldn't see this causing the problem?