Can someone suggest what may be causing the following.I have a 1999 Octavia 1.9sdi which I know is not the most powerful of vehicles but Im happy with it. In feb this year the fuel filter plugged,I can only presume that I picked up some poor quality fuel. Changed filter all was well for a couple of weeks after which the car seemed to develop a flat spot/hesitation in third gear approx 2500 to 3000 rpm,mainly when under load for example going up hills. Had car serviced mid may explained symptoms to mechanic who again changed fuel filter and told me that there where brown oily deposits in the filter that he took off,bearing in mind this was only a couple of months old. Again car ran ok for a couple of weeks but hesitation has once again returned. Ive drained the filter and clead diesel is comming out. What else should I check and is anyone aware if there is any form of filter in the fuel tank that may have clogged.

Have it fault scanned, it's the first step. Also get your case pressure relief valve in the pump checked - the gradually fall out which can cause timing issues giving the symptoms you describe.

I'd also have the static timing checked via computer.

If you post a copy of the fault scan report from your service I'll be happy to have a look. But you should have it rescanned now you are having an issue anyhow.

Greg.