I have an 03 F250, 5.4 with 99K miles and it's rough upon start up for about 10-20 seconds and then smooths out. I replaced the IAC valve, did the fuel filter about 5K miles ago, new plugs recently, injector cleaner, cleaned the MAF sensor and the throttle body. It does it worse when it's cold......

My only thought it that one of my COPS is about to go bad. Any other ideas????? Thanks!

 

When was the last tune-up? When were the spark plugs last replaced and what brand did you use?

 

about a year ago. I did replace all the plugs....I don't remember what brand.

 

I don't think it has anything to do with the plugs; if it did it wouldn't get better as the truck runs. For the same reason I don't think it's a bad COP, because most of the time when coils fail they fail when they are warm.

I'd recommend scanning with a good scan tool and investing in a fuel pressure gauge. I'm guessing that your fuel pump may have a hard time building pressure when it's cold.

 

Hows the coolant.. Head gaskets leak into the cyl and cause starting issues when cold. Check a plug They should be motorcraft for sure and not bosch.

Dick

 

Also check out the COP boots themselves, may have a bad one

 

I like your thought about place possible coolant leak, but that would be a rare failure.

But I have Bosch plugs in mine and it runs just fine. Never have heard a good explanation as to why non-motorcraft plugs can cause problems.

 

The bosch plats and others seem not to like some engines to the point of running like crap. Being a mechanic for 35 years I don't have an answer why. I just have experience with them and many other folks reporting the same.

Dick

 

Any other thoughts......????

 

Would a bad fuel pressure regulator cause this problem????

 

Need to find out fuel pressure when cold and and warm. Without that your throwing parts at it

 

Perhaps a bad air temp sensor, dirty MAF, bad or dirty IAC (even though you did replace it), throttle position sensor, O2 sensor, or a vacuum leak would cause this issue.

 

My thought would be a leaking injector flooding a cylinder out. You start it, and it clears up. Read the codes for a misfire, and see what cylinder shows up. Im sure there are codes, just not a mil.

 

I agree. Either that or coolant in the cyl. Very hard to diag..
How long does it take after stop to happen again?
Again its hard to diagnose. An experienced mechanic might have a much better chance at finding out whats wrong by just listening to how it runs.
or not running..



Dick

 

I'm following this thread. My 2003 F250 with the 5.4 has started doing this recently. Only happens when it's cold and wet outside and takes 3-4 miles down the road to clear and then no problems at all. Even then, it's intermittent. When I left work the temp had dropped 15 degrees today and it rained all day, but no problem at all. I had it scanned at Autozone and it came up with P1152. I'm going to start taking everything apart and cleaning everything I can to see if I can get the intermittent problem to not show at all.