The Disco has been consistently experiencing rough, warm starts.

Like... morning cold start (normal) > drive to grocery store > shop for 45 minutes > start car (very rough).

It's rough just while idling and then the moment I start driving, it's smooth as glass. Usually I'll get an error code followed by a CEL. Most of the time it's only P0308 but sometimes it's only P0300. I've checked spark and air extensively, so the only thing left in my mind is a possible leaking injector? Perhaps stuck open a bit and flooding the engine while it sits warm?

I ordered a new one to swap out with injector #8 to see if that helps. Should be here soon, I'll report back.

 

Use scanner to see if fuel trims and O2s are normal (to rule out vacuum leak). Maybe spray clean the throttle plate and IACV if it's been a while. Visually check throttle for oily gunk. The position of the IACV changes warm vs cold and impacts other parameters (vacuum, injector pulse width, ignition timing). I think if a cylinder was gas soaked in a parking lot, it would clear up quickly while idling. Another suspect is CKP sensor. Maybe try a known good sensor before attacking the injector. The CKP sensor is what detects misfires, so might be a clue.

 

Throttle and IACV are sparkling clean. CKP is brand new too and all good there. Wiring harness tested from the sensor all the way back to the ECU.

The only thing I haven't monitored are fuel trims. O2 is good.

 

Do you have the factory cps cover on? Did you wrap it in foil? Sounds like a heat soaked CPS.

 

Cover on and wrapped in foil

Also, where I live it just never gets much above 70.

 

Hmmm, have not heard of a heat soaked MAF failure but you might try unplugging that on next hot start. Could be a leaking injector but highly unlikely. You could test by dumping the pressure on the fuel rail after a warm run, see if it starts ok. Or maybe monitor 02 voltages on hot start, if you have a leaking injector one side should be very rich on start. Or pull the fuel rail and jumper fuel pump relay and see if one leaks.

 

I hate to admit this because it feels so newbie, but I pulled the spark plugs yesterday and feel like this might be the problem. I replaced them in 2019, and about 80K miles ago, but the ones I put in weren't double platinums. Only single, NGK, which according to the internet and NGK themselves, last about 30-40K miles. The electrode on cylinder 8 is also the more worn, which might explain some of the issue? I have Champion 7070s on the way today.

Cleaning out the injectors today too while they're out.

 

It sounds like you got to the bottom of it!
Nice looking rigs, and cool license plate numbers!

 

Good on you! Worn plugs makes way more sense than a leaky injector. Maybe due to differences in spark advance hot vs cold, or simply the air/fuel mixture (harder to jump the gap in lean mixture). Did you measure the worn gaps? Amazing how fast 80,000 miles go by.

 

Alrighty - updates.

Installed the new sparkies. They were much needed regardless of this issue.

Also cleaned the fuel injectors while they were out. They didn't seem that dirty to begin with, but figured it couldn't hurt. Basically rigged up each injector to a 9V battery while spraying carb cleaner through a little jig I made.

Got everything put back together and gave it a test drive, smooth as glass, BUT, when I did the thing where I started it ~45 minutes later, rough idle again. Also, it's not rough as in rpm-is-bouncing rough. It's more of a misfire feel? Hard to describe. While it was doing its rough idle I took a video of the O2 readings. LMK if maybe you all notice something I don't.

Another thing of note - while the upper intake was off, I noticed that the rocker cover gasket I installed in 2021 is pretty dry and shows cracks on the outside. Zero oil leaks, dry as a bone, but is this a possible issue? Possible vacuum leak?



Dry/cracking rocker cover gasket