2015 5.0L Rough Idle on Start, P0300 Code/CEL

Hi everyone,

Just thought I'd start a thread on here about an issue I'm having. The car is at the dealership and has been since Tuesday May 16th.

The motor is stock right down to the OEM air filter. There is no tune and never has been.

I had the oil, transmission, rear dif and brake fluid changed at the dealer May 8th and then a lapping day at a local short road course on May 11th. The car performed well at this event. On Sunday May 14th I noticed a rough idle on start up. It only lasts for about 10 seconds and then the engine runs normally and there are no driveability issues.

On Monday May 15th, same rough idle at start up only this time the CEL came on. The engine again smoothed out after about 5-10 seconds and drove fine. My OBDII reader said P0300 - random misfire. Unfortunately this code isn't very specific and no other more specific code registered.

Took the car into the dealership Tuesday May 16th and advised them of what was going on. They've had the car since that time. When I last checked in, they said they acknowledge the rough idle and P0300 code but that they can't determine the cause at this point.

They are in communication with Ford Technical Support to determine the issue. I'm rather surprised it's such a mystery considering the motor/drivetrain are all stock, however, I will wait for their diagnosis.

I will update when more information becomes available just in case others will experience this problem.

Mine is at the dealer today for the codes p0300 p0305 and p0308, I have a scanner. supposedly they are misfires, the 305 and 308 identify cylinders I believe. Mine is there also for the rear view camera, harness. Of course they said they ordered it, and it came in... reality they only ordered the camera... boooooooo

BTW, mine is a comp org 5.0 also.... color cant be the reason... ;)

look forward to what they say for both of us.

Bad gas? Fuel pump?

Checked with the dealer yesterday. As per Ford Tech, they will be checking injectors, fuel rails and intake runner control. Will update again when I hear more next week.

They did a compression check and ended up resetting the PCM along with upgrading some firmware. Guess what, check engine light came on again on the way to work this am. I'll be scanning it when I get home. Not happy...

My car is still in the shop and won't be looked at again until tomorrow (it's a holiday up here today).

The dealership owner emailed me the other day just to keep me in the loop. He basically said they went thru their normal checks and then contacted Ford Tech. He said when FT gets involved, they basically have to go thru the checks they ask for and then send them the results. They then wait for a response. Then repeat the process with new test instructions. The dealership owner acknowledges it's a bit of a time consuming process but one that must be followed in the event of a warranty claim. He said a motor could have a hole in the side of it but that they'd still have to follow the instructions from Ford Tech on going thru their check-list.

As I said above, at this point they will be checking the injectors, rails and intake runner control. I also put a bug in their ear about the crank sensor, so we'll see what happens.

The rough idle issue only lasts until right after initial start up and the car runs totally fine after that so I can't see it being something internal. To me it seems to be that the car doesn't recognize air/fuel conditions on cold start and has a problem. After it's even a bit warm, it reads everything as 'ok'.

I'll say again that I am surprised the issue is such a mystery considering how many of these cars have been sold and the not too uncommon condition of 'random misfire'. However, I will be patient and wait to see what happens.

My dealer has been excellent, however. The owner personally advised me that he considers me a VIP customer and that they will get the issue resolved and ensure my car is taken very good care of while in their hands. That was really nice to hear.

UPDATE...

They went through a bunch of stuff Ford Tech asked them to check out. In the meanwhile, I advised them of some info I found on forums regarding similar issues involving the crank sensor.

So, being the awesome dealership that they are, they actually further investigated this avenue and ultimately ended up ordering a crank sensor and installing it...

And... FIXED!

No idle issues on cold start and the car runs perfectly otherwise.

awesome! I am still waiting for my callback to hear that the harness is in... Its been a week...

Very good sounds like a nice dealer.

So, did a track day last Thursday and now again I have rough idle on startup. It's smooths out after a few seconds and drives fine.

The research I've done says that some crank sensors can malfunction due the higher temps and where the sensor is located on the rear of the block.

So I suppose I will have this replaced again.

I may look into rigging up some kind of cooling duct/hose from underneath or the front of the car to the crank sensor area and see if that makes any difference.