03 v6. Not sure exactly what’s causing the car to run rough for 5-10 mins on startup but definitely something going on with the Ecu. Once it’s fully warmed up misfires go away and car run perfectly normal. Hoping it’s dirty or loose wiring behind the glove box where Ecu is but might be wishful thinking.

 

Nobody else brave enough to take on this one?

Some more details would help. Is this a reliable daily driver with a new problem out of the blue? Derelict dragged out of a field and this is the first time it's ran in years? Something in between? Any recent work on the car, even if seemingly unrelated? Any OBD fault codes?

As far as suspect components? The computer itself would be way down on my list of likely culprits, after the spare tire and rear view mirror.

 

I’ll jump in with you Karl.

Definitely need more info. I’d start with throwing an OBD reader on and checking for codes, even if there’s no CEL.

When you say warmed up, is that centered on the temp gauge?

Is there a difference if you let the car get to temp via idle or driving?

Have you checked all fluid levels?

Have you disconnected the battery recently?

How long has this been going on? Has it happened before?

 

That was my first take on that as well - as Karl wrote: ECU more like last on the list - a ECU does not warm up...
Maybe the catalyst wants to warm up first, as there is something wrong.
Maybe the spark plugs are long overdue, but after getting warm, they still just do their job?
And fluid levels? And battery? Is it better, if your charged the battery with a charger before starting?

 

So I purchased her about 4 months ago. Car is perfectly fine to daily so long as I wait for her to warm up. It only recently started doing this out of the blue. Odometer has 244000 km. Obd gives me the obvious misfire codes on all cylinders when it’s doing this but I replaced the plugs and coils already. All fluids good, temp stays solid in the middle and the v6 is surprisingly quick and runs like new. Previous owner seemed to take decent care of it but there’s no telling if it sat for a year or two or not at all. It’s more of a project car I’m bringing back to life for my son but he definitely drives it every day without any issues other than 10 mins to warm on cold start. Other codes I get are p1316 & p1314

 

Agreed, it's not the "ecu" (you mean PCM aka ECM).

What are the fuel trims? Hot engine, parked. At idle and about 2500rpm.

You may have an air leak or damaged cats or ... well, let's see the trims.

 

Your symptoms plus p1316 & p1314 tell me that if it is not the catalyst, the likely culprit are the piston rings, which are worn, or even worn cylinders (or valves). Because, when the engine is cold, you got low compression. However, after 10 min. the faulty parts have heated up, expanded and thus they seal again (even though they are worn) and you have better compression again... That's my 5 cents worth...

 

I think Peter is on the right track, something is changing with heat, giving you the better experience when its warm.

I’m shooting from the hip, but perhaps there is a ton of carbon on the valves? This is common on GDI engines (the S Type is not) but cold GDI engines can run rough at cold start, then even out as it warms up. This is unlikely, just a guess. I agree, fuel trims would be very helpful. Maybe that fuel pump isn’t happy when she first starts. Could also be a vacuum leak somewhere, again, a guess.

Something you could try…disconnect the battery overnight. This should reset any previously learned strategies and trims. Reconnect the battery and perform the throttle body reset procedure. (See Here). Can’t say it will change anything but couldn’t hurt. If you choose to do so, remember the transmission will need to relearn its shift strategy during your first few drives. Drive smoothly and moderately to help this process.

——-

Some more questions…sorry, not trying to put you through a 3rd degree… just trying to paint the picture.

- Do you have a vacuum gauge to check vacuum levels?

- Going to assume you used quality plugs with proper gapping and coils with a touch of dielectric grease, correct?

- Any rich smells or excessive smoke coming from the exhaust?

- At cold start when the engine is idling rough, do the RPMs jump around or stay relatively in the same range? Does it idle high?

- Before the car warms up, is it drivable or idling so harsh you are forced to wait?

- Since you’re getting codes, I’m assuming your CEL is on. Does it blink at all? Does it go off after the engine is warmed up?

- Anything else odd going on, such as poor mileage, rough shifting…etc.?

 

No blinking cel & sometimes it doesn’t even come on. This is a new issue so I’ve not had time to really check much but I may try different plugs to start since I bought auto lite copper plugs. The shaking does make it impossible to drive for 5-10 min on cold start and it idles sporadic and at about 1000 rpm with the lights sometimes flickering. I will check a few more things but since my son takes it to work in the morning it’s hard to duplicate because engine is always warm

 

Timeframe for when you changed the plugs and coils, please. Was it in response to the current problem? Or were they changed for some other reason and then the problem started? Not trying to bust your butt, just trying to piece together some little clues.

What brand coils did you install? Please oh please oh please tell us you installed a quality name brand such as Denso, NGK, etc. There are many tales of woe on the forum of bargain brand coils causing grief, especially those eBay no-name specials. House brands from the discount chains haven't fared much better.

You mentioned copper plugs. No idea how copper would behave, but I'd highly suggest replacing them with OEM spec plugs. I think they are irridium or platinum or some other exotic metal. The copper plugs likely have big blunt electrodes with lots of mass. Just a guess, but maybe it's taking a long time to heat up and so you get rough running while cold. Can't guarantee that's the problem, but I'd sure want to try the proper plugs before going into FullPanicMode.

 

If Karl is right and it is the plugs (or the new coils)...:
I went for the imho best plugs the market has to offer: Denso Iridium TT (two needle thin electrodes).
Denso IT20TT - that is for S-Type 3.0L and 2.5L

And while we are at it:
It's IK16TT for 4.0 and 4.2L S-Type
It's IT20TT for all X-Types
It's IK16TT for X308 3.2L
and IQ20TT for X308 4.0L

 

Had a bad misfire on cylinder 3 so being that it was a new purchase I did all the plugs and coils. The coils are Delphi. Thanks for all the quick replies. Just strange because literally the car runs like new since buying it and even now once it warms up it flies. I’ve only changed the tires, coils & plugs, belt, squeaky idler pulley and mirrors since getting her. Will investigate further this weekend after a cold start or two I should have a little more info.

 

May be bad coils.

But be sure to do the fuel trims as they can rule things in & out.

 

My guessOmatic says something in your cold start system isn't functioning properly. Engines purposefully run very differently when they're cold, typically a richer F/A ratio. I have no idea how that works on this engine but does souund like your engine isn't doing this.

 

It may be. It's a combination of time, IAT, ECT, what the O2s do, and so on. Not worth exploring (in detail) as yet.

If interested, watch IAT & ECT - after the trims!!

BTW it may well be damaging the cats so don't wait.

 

What's with the wacky rhetorical question? Does a bear $#!+ in the woods? Is the Pope Catholic?

 

Ah, as Paul Harvey would say: The rest of the story. Let me make sure I have the timeline correct. Car is new to you, only major issue is low power (aka misfire*) on cylinder number 3. You changed that coil and plug, a reasonable plan of attack for a localized problem. Unfortunately, "while I'm in there" syndrome seems to have backfired on you this time. You changed all the other coils and plugs, too, and a new problem reared up.

If I'm reading between the lines correctly, either some of the new components are bad, or something else was disturbed (a new vacuum leak?) during the removal/installation process.

Delphi should be a good brand, but I have no experience with them.

Do you still have the old coils, and hopefully kept track which one came from the #3 position? It might be worth reinstalling those 5 known good coils and see what happens. If you don't know which coil was suspect, install all 6 and see if the problem reverts to a misfire isolated to a single cylinder.

As previously mentioned, I'd also lose the copper plugs and see if expensium plugs make any improvement.

Perhaps before changing any more parts, check for vacuum leaks, in case there was a problem during reassembly. Here's a good primer on the subject:

JagRepair.com - Jaguar Repair Information Resource


Ah-ha! The rear view mirror! Did I call it or what?



*[Soapbox mode] If the computer has set a misfire code, please be aware "misfire" wasn't the best terminology that could have been used. Misfire sounds like an ignition problem, at least to me, meaning the fuel and compression were there, but for whatever reason, the required spark was missing or weak. This might lead an aspiring mechanic to troubleshoot the daylights out of a perfectly good ignition system. I do not care to discuss how I know this.

In OBD-speak, misfire simply means one or more cylinders is putting out low power compared to the others. Pretty much anything affecting the output of a cylinder can set a misfire code. It can be low compression. It can be a valve not opening fully. It could be a clogged fuel injector. And yes, it could be an ignition problem, too, but don't overlook the other possibilities, too.
[Soapbox mode off/]

 

Ooh, excellent idea. Doesn't cost anything but a little bit of time.

 

hahahaha side mirrors not rear view but I did have to secure the rear view mirror also. will definitely try disconnecting the battery tonight. After changing the plugs and coils everything seemed fine for a while so not sure if it’s coils. but with so many things to rule out I’ll get the fuel trims and go from there.

 

If you disconnect the battery you will have to wait for the trims to relearn. Better to look beforehand!

Also, before disconnect check which OBD monitors if any are not set. They'll all be unset after the disconnect.