Is your check engine light on? Any codes?

I would check all the vacuum lines for cracks and proper connection not just the two I mentioned before.

If the egr valve is stuck open you can some time tap it and it will close. One way of testing it is to connect a hand vacuum pump to it in place of the vacuum line and slowly apply a vacuum (with the engine at idle). A plastic syringe (35 ml) and a small piece of tubing can be used in place of the vacuum pump. If the valve was closed initially and and opens under vacuum the idle should change. The engine will noticeably stumble. If you get no change, then either the valve is faulty or there is a blockage in the egr tube.

You can clean both the egr valve with carborator/throttle body cleaner. Sometimes this restores function.

Your DPFE could also be faulty or the line leading to it could be plugged.

Another possibility is if you have a visible exhaust leak this could be allowing air in to the exhaust causing the oxygen sensors to give incorrect readings.

There are several possibilities so it would be helpful to no if it has thrown any codes or if there are any pending.