Nissan Teana cold start problems Troubleshooting

Mileage over 230,000 km of the 2008 Nissan Teana sedan V6. When you start the car, there will be idle flameout phenomenon; cold car takes 20 ck200 key programmer seconds or so to start, and after starting the engine shake obvious dithering hot car slowed; turn off immediately after the restart, normal can start. If you turn off more than 1 minute, and then start more difficult.  
Failure Analysis:    (1) First, to start the power check test results between the battery voltage 12-14V, exclude battery failure;    (2) then check the oil pressure, fuel pressure gauge connected to the oil, start the engine, the fuel pressure measured at work, oil pressure is 290KPa. Ten minutes after the flame, measured normal oil pressure 219KPa. Fuel pressure were within normal range.
   , the resistance and the obd iphone high-voltage ignition coil resistance were within the normal range.    (4) Check the crankshaft position sensor resistance between 950 ~ 1250Ω, throttle position sensor resistance between 1-9kΩ, were within the normal range. (5) Taking into account the engine wiring harness, plug, wire dissolved if there is a problem and there is connected to the line, all were normal, and then check the cylinder of each cylinder pressure, the pressure in 900Kpa above, are within the normal range.
(6) confirmed that no more than a few parts of the fault, once again on the point of contact for each thread to be checked to clean up, each terminal autohex ii connectors have not found the problem, then the car can be properly started. Over three days, could not beat the car breakdown phenomenon occurs again.    (7) the car in the shop customers do in-depth examination, cold the next morning to check the above items, test results Step 1 Step 5 are consistent with prior to Step 6 found that the cylinder pressure is not normal, of which there are two a cylinder pressure is relatively small, the other four cylinder does not exceed the maximum cylinder pressure 200Kpa, therefore open the cylinder head, and found that the valve has not closed the door seat and valve tappets have formed around 2 ~ 5mm thick coke see the top of the piston valve has been out of the top few rows of the ditch and India. Under this situation, the quality of gasoline is suspected, open the fuel cap, and immediately smelled a pungent taste. So take a moment
(8) to clean soot around the valve seat and valve lifter, as well as the valve re-polished, no other problems after the confirmation. Reinstall the cylinder head, replace the car petrol car. Then start the engine, failure to lift.