Recently my 2003 4.6 has been idling rough, and times it will eventually stall. So, I replaced air filter, cleaned the MAF sensors, and replaced the IAC. Did not solve the problem. What else can I check before I have to take it to a shop? Do I need to wait for the "check engine soon" light to come on before using a diagnostic tool to read codes?

I would appreciate any comments. Thanks

 

could try cleaning the throttle body, and seafoaming the vacuum lines to clean the injectors.

 

Seafoam via the vac line did not help, in fact did not see any smoke out the back. I found the hose cracked at the PCV. Replaced PCV and all related hoses. That was the problem. it now idles smooth, no stalling