when i first start it it runs rough and doesnt idle high then go low, it stays at about 550 rpm all the tme at idle.

when u drive and hit about 50kms/hour it drives perfect, even in idle when its shaking and i press on the gas in park it runs rough till the rpm hits about 1500 to 2000.

I put some lucas injector cleaner for diesel in the gas tank and drove it on the highway for about 2 hours, when i was back i could tell it was running a little smoother, but still rough, and the acceleration improved, but still sluggish, but when the A/C is on, it gets worse as usual.

i did change the fuel filter in the engine compartment, but i had this problem before and after.
seems like its not getting enough diesel at idle, so when i give it gas the pressure goes up and it gets enough.

but when driving over 50, it drives perfect and smooth.
I left the car at the diesel mechanic today, tomorrow I will check with him if he found something wrong, but he told me might be a bad injector, so he might do a compression test on it.
I dont know much about diesels, its my first one.