A few months ago, I noticed that my Ford Explorer idled somewhat roughly. Consistently, this would happen after the engine warmed up. I began wondering if the engine was misfiring at idle. Finally my suspicions of a misfire came true when the engine light came on about a week ago. The codes being put out were PO171 (Bank 1 Lean) and PO303 (cylinder 3 misfire). I had recently changed out all the spark plugs and coil boots, so I was very skeptical that this was the culprit. However, I went ahead and inspected as well as replaced the spark plug .....nothing changed. I then decided to replace the actual coil pack and again the engine misfire still occurred at idle. I only notice the misfiring taking place at idle, and not accelerating or driving. After reading other forums and doing some research it seems as though it could be an intake leak or an issue with the fuel injector. I have not owned this Explorer for very long and the odometer just hit 150,000 so the truck has a lot of life left in it. Just curious if anyone had similar experiences. I have yet to read a thread that describes a rough idle and misfire only at idle when the engine is up to temperature. When the engine is just starting up and is cold there seems to be no issue at all, until its been driven around for a bit. Any help on the topic would be much help!

 

Based on the diagnostic codes you have and your description, it seems likely the issue is with either the fuel injector or a vacuum leak. The lean code could suggest you either getting too much air (vacuum leak) or not enough fuel (injector not firing). It's pretty common for the connectors at the fuel injectors to become brittle over time and the locking clips break during service. Often people use cable ties to hold the connectors tightly to the injector. A vacuum leak could be due to an intake manifold issue or other leak.

-Rod

 

 

Awesome, I'm glad to hear you got the issue resolved! Good work.

-Rod