Cadillac Forum - Enthusiast forums for Cadillac Owners - pinging on my northstar 2003 Cadillac sedan Deville

1. I have a 2003 Cadillac sedan Deville with 165 K.
The car has always used 1 quart of oil for every 1000 miles.

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In the past month I have noticed a pinging in the motor once it has completely warmed up.

A week ago I went to start and it would kill immediately unless I kept my foot lightly on the pedal. No drivability issues just would kill when I let off of the gas.
Service engine light was on (map sensor code)
I pulled the egr valve off and used carb cleaner on it.
The car ran great and did not kill again. I did not hear the pinging at all for about 4 days and now it is back but not as severe as before. It is defiantly a ping.

Here is my question: Should I spend the $160 and put a new EGR valve on the car or is it carbon on top of the pistons that is causing the problem?

Pinging is not good and I need to get this fixed quickly.

Your knowledge and advice is much appreciated!!
Sincerely, JW