98 Mercury Mystique EGR Valve

My wifes car has the check engine light coming on. The code says it's the EGR valve not having sufficient flow. We had the valve replaced but they never cleaned out the pipe it connects
to which we were told needed to be done. So is there anything we can put in with the gas to clean it? Like these additives you can buy. Or would we have to take it to a garage to have it cleaned. We've been quoted 'about' $600 to have this done which seems really high.
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Alex Devlin

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Alex Devlin wrote:

I am going to assume that the Mystique EGR system is similar to that used in my Focus. The topic 'Insufficient EGR flow' comes up on various Focus forums a fair amount...
It's a reasonably good possibility that the EGR flow is sufficient, and that the problem actually lies in the DPFE (Differential Pressure Feedback EGR) sensor. This is a solid-state sensor that measures the pressure drop across an orifice in the EGR tube. By measuring the pressure drop, the computer can calculate the amount of flow. These sensors are notorious for going bad. I would check out the EGR pipe for obstructions, make sure the pressure sampling ports are clear, and the rubber hoses connecting the ports to the DPFE sensor are also clean and in good shape. If there's no trouble found there, you may need to have the system diagnosed (there's also a solenoid/regulator valve controlled by the computer that controls the vacuum supply to the EGR valve) to see if either the DPFE sensor or vacuum regulator valve are bad. If you want to shotgun the diagnosis by parts replacement instead of paying for someone's time, I suppose you could replace those parts. I'd replace the DPFE sensor first, if the tube(s) all check out.
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