Need some help here. I'm having a problem with my 05 fx4 idling once warmed up. The truck runs great on the hwy and also on the short trip to the store.

The odd thing is this started the day after I changed my oil. I did put synthetic oil in this time. Would this have caused a problem?

The truck has 165 K on it. I changed the plugs and fuel filter about two months ago and the truck has been running great up until the oil change. The oil level looks fine.

After driving it for about 20 min the idle issue will start when in traffic or coming to a light. It's also seems more pronounced when going into reverse.

It sounds as if several of the cylinders are cutting out. If you tap the gas it will recover.

 

Clean the maf and the throttle body with the appropiate cleaners.....

also check the fuel pump driver module....

get a code reader and check for codes....

what spark plugs were used? how many miles?

 

I used Motorcraft plugs, have 165 K on truck. The CEL is not on so I don't think I will be able to pull any codes.

 

You can have codes without the CEL being on. How many miles on the plugs?

 

Ok, looked again and if only two months on the plugs, probably not them. Have you looked for a vacuum leak?

 

Hate to be the guy who suggests it but have you checked the compression? Maybe a head gasket. This sounds exactly like what happened to my diesel at 150K.