why is my lexus RX is closing off while driving and smoking. I change the knock

Best bet would be to have a shop take a look. I assume when you say "closing off" you are saying the engine stalls? Smoke may not have any relationship to the engine stalling, maybe an engine oil leak? Lexus stalling could be caused by a bunch of different problems. Might be a simple vacuum leak or sensor issue. Are there warning lights lit up on the dash? This may help a technician accurately diagnose what the problem is. We do offer free inspections and test drives, and may charge for diagnostic work if needed. Don't hesitate to give us a call, we are here to help. Erik Herman All Pro Automotive 904-241-4800