I have a 2023 5.0 with about 22k miles , when it’s cold it starts normal every time. After it’s warm it will start right back up after shutting it off , but if it sits for an hour or two it will sometimes seem like it’s barely going to start. It barely idles up after it fires, it seems to fire very fast, faster than normal almost like it doesn’t even crank its immediate but has a crazy low idle for maybe 3 seconds or less then it’s fine. I had it to the dealer but there is no code and they said they couldn’t replicate it so they sent me on my way. Any input is appreciated

 

I wish i had that problem. Mine is the opposite. When it sits for about an hour or less it immediately goes to high idle an stays there for about 3 minutes even though the water temp is almost full hot. Cold it high idles for about a minute and than lowers idle.

 

Almost sounds like heat soak. This was an issue common to 97-06 TJ Wranglers where the residual heat from the engine would cause the fuel to boil inside the injectors and thus the injectors would spray gas vapor for a few seconds until liquid gas made it through. The permanent solution was literally just to add a small piece of insulation to the fuel injectors.

 

That's probably an emissions thing. It wants to light off the catalytic converters as fast as possible to reduce startup emissions. It's possibly also to prevent damage to the catalytic converters from a more explosive light-off that might occur if you started flogging the engine right away. Overall it's actually protective for the engine (and turbos, if applicable) since it pushes oil and coolant through faster.

Some cars will also do it for AC and even heater performance. The F-150 boosts minimum idle for AC at least. Sometimes turning off the HVAC will cause it to go to low idle faster.

 

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If it were me, I would be looking for either low fuel pressure or injector flooding some cylinders.
If not found, then looking at possible Throttle Body issue.
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As for high Idle its normal and part of Emissions self testing.
Every time the engine is started this Test is entered.
The fuel is adjusted lean, or what the test program commands, Idle is raised to get the CATS heated.
The test looks for a 40% rise in Cat Temps within a specified time.
This is how the Cats are tested functionally to meet federal standards for Oxygen content in their output end as detected by the rear Ox Sensors.
If there is a failure, codes 420 or/and 430 may be set to tell you about it and a check engine light comes on.

My 2018 does it every time and I have watched with a Scanner looking at live data to see it happen. Watch the cat temps begin cold, rise then return back to normal as the Idle RPM drops with it. The Cylinder head temperature is also part of the test and affects when and how fast the Idle drops according to outside Ambient as well.
Things are just not a simple as would be assumed.
Good luck.

 

Would forscan show me fuel pressure ?

 

I don't have Forscan but would assume it can, the same as a good Scanner does.
There is the prestart pressure at around 60 psi, as engine starts, the pressure will rise from the high pressure pump operation to a value well over 1000 psi and as high a 3000 psi depending on what is commanded and other conditions detected
The low-pressure pump feeds the high pump to raise the pressure for direct injection use.
These are two separate systems for pressure. Low for port and high for direct injectors.
Good luck.

 

Okay thank you

 

 

Does this mean anything to anyone or am I looking at useless data , this is sitting with ignition on, haven’t really figured out the FORScan yet