Now that I think about it, I had a 91 Mitsubishi that had a temp sensor on the EGR valve. The temp sensor or EGR valve went south and caused a check engine light. I don't think there was a change in performance. The point is that if your car checks the temperature at the EGR valve, it may notice that you've blocked the passage. But I think it's such a simple thing to do yourself that it's worth the exercise.