2003 ml500 I've had this vehicle since it was new and it always started up as soon as you turned the key, but now it takes 3-5 seconds before it starts. I have the obd2 code reader and every thing checks out ok. Could someone please tell me what the problem maybe?

 

Replace the fuel filter- sounds crazy but it fixed my issue after looking at MAF,MAP, camshaft sensor, crankshaft sensor, etc.