Poor gas mileage after tune up

this sounds like it could use a tune up. rough idle could be a sensor or poor ingintion.

Sorry guys i was late with my feedback... So here it goes.. I have no check engine light.... Currently running the stock tune as well.. The car has no tps, pcv or egr valve.. It is all controlled by the electronic throttle body which i recently cleaned but didnt help with my problem. I ordered a new fuel pump as well, just didnt get the chance to install it yet. Cant change the fuel filter as it is builtin within the pump. However, shouldnt the fuel pump or fuel filter cause engine stalling, bucking and hesitation? I doubted the fuel pump could be causing this since the problem only occurs at idle. By the way, there is no missing on any of the cylinders.

Check your spark plugs.

tune up,fuel filter,air filter,

It may be time for a tune up for your 9 year old car. You don't state the mileage nor when the last tune up may have been. Rough running can be many things including but certainly not limited to: dirty or poor operating injectors, poor engine timing, dirty air, fuel filters and a host of other items that will be corrected during the course of a normal maintenance tuneup. Please discuss your concerns with your Volvo diesel mechanic.

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remove the head and grind the valves in,also renew the valve guide seals at the same time and make sure the tappets are set right

Look inside the throttle body with a flashlight. If the intake manifold looks wet or is cleaned off inside, then the SFI fuel injectors are leaking. This will cause poor performance and poor fuel economy. If this is the problem, have the injectors replaced with an upgraded MFI assembly.
Also you did'nt mention spark plugs, check/replace if you have not already.

Sounds like you're missing on a cylinder or two. Tune it up, first. That might very well fix your problem. Tell the part store guy you need a COMPLETE tune up kit and replace everything that he gives you parts for. Not just plugs and wires, although they would be better than nothing. I'm pretty sure this will fix you up. The symptoms you're describing are classic for a tune up.

If it has NOT had a TUNE UP In A Long time THIS is MOST Likely the CULPRET as what you discribe ALL can be attributed to POOR TUNE Up PARTS.

if your exhaust system is not up to factory spec this will cause idle and rough running conditions,as well as the poor fuel economy, this is due to the sensors not getting accurate readings and sending skewed info to the onboard computer, (the exhaust system has as many as 3 sensors, although i think yours has only one, if you can also remove the catylitic converter, you will get more power./better fuel economy