Start the 2000 5.4 Liter. Higher than normal idle when cold. Check engine light stays on now every time I run it though the idle is now OK. Second time this has happened from a year ago.
First time I dis-connected the battery to shut off the CE light on the dash.

Thoughts? Temp sensor going bad?

 

Yes, scan it for codes.

 

Good point. I’m considering this scanner with good reviews and low price.

 

"When cold" is typical of vacuum leak. The engine warms up and the leak seals, but you get a lean code while it's cold.

I have that reader and it has worked well. It has freeze frame and live data and pending codes. Freeze frame shows the engine conditions when the code was set. You'll need to download an app to work with the reader. I used Piston but there are other ones out there.

Note that the one you showed only works with Android or Windows. Not iphone.

 

Thanks for the input. I will look into the Apple model and get it ordered. Weird that it’s so infrequent and only does it once.

 

There's a time factor involved and number of start cycles, I believe. It has to run lean for a certain amount of time and it has to do it so many times over so many start and run cycles. I had a similar issue with my 4.2, I cleaned the MAF and reset the PCM and it went away but then came back a month later. The weather got colder, I probably let it idle longer instead of just taking off, things like that. Freeze frame showed that the code got set when the engine was cold. It was the isolator bolts, fairly common for the 4.2.

Anyway, that's the beauty of the OBD reader, you can see what the PCM is doing.

 

Got a used scanner off eBay. I will post my findings when it gets here.

 

Got the Scanner. One Code:

F150 OBD Code P0705 Transmission Range Sensor Circuit malfunction (PRNDL Input)

Interesting because I have also have a occasional case of “turn the key and nothing happens”. This is a known issue with the TRS switch on the tranny going bad. If mines external (2000 5.4).
I will gladly replace it. When it doesn’t start no code is ever shown. A re-occurring theme on here. More info:

Symptoms of a P0705 DTC may include: Malfunction Indicator Lamp (MIL) illumination with P0705 DTC code set The backup lights may fail to function It may be necessary to move the gearshift lever up and down slightly for a better contact to allow the starter to actuate and start the engine It may be impossible to actuate the starter In some cases, the engine will only start in neutral May start in any gear Irregular shift RPMs Drop in fuel economy The transmission may display a fault.

 

Ordered the Dorman external TMS switch for $32. Sprayed the bolts with PB Blaster to get it ready for replacement. Front driveshaft is in the way but it shouldn’t be too bad of a job.
This should fix the dead ignition issue I’ve been getting from time to time.

 

Well the ignition switch wasn’t too bad to replace. I would highly recommend wire bushing the exposed threads of the cable arm then spraying them with penetrating oil a few times.
The front drive shaft is in the way, still was able to do this just lying in the driveway. The switch has two different mounting holes on one end. I had to use the one closer to the shaft hole. Also the metal spacers on the Dorman replacement part part were too long. Tapped the OEM spacers out with a punch and gently tapped them into the new switch. Long spacers shown on old switch.
https://photos.app.goo.gl/py3PmTQD6EryKsMy7