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Discussion Starter · #1 ·
Hi All!

New member here posting for the first time!

Last week I picked up an 04 RR with 73k on it. The truck has been running great, with an exception; during a cold start, the idle will be rough and the engine will misfire a bit. After the engine gets 1/4 of the way to running temperature, the idle smooths out and everything is just peachy.

I replaced the MAF sensor hoping that it was the issue, but it seemed to make the problem worse. I'll be swapping that back to the original part later today.

Any thoughts on maybe plugs/wires? I have a hard time believing that bad plugs/wires would only cause an issue when the engine is cold. I am assuming that they are original.

Thanks in advance!
 

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Unless you live in a desert, you're going to have moisture. You'll get condensation. If your wires are marginal, that moisture can cause spark leakage to find its way to ground.

Even if they're not bad, you should have a good 8mm silicone wire on your truck anyway. It's one of very few mods above OEM that has positive benefits. And, at 73K, it may have the original plugs in it. That's a low mileage truck you found.

You didn't mention if you has a SES light on or blinking. If not, your rough idle may be from some other issue. A dirty throttle body can cause these problems. Does the misfire go away when in gear and slightly off-idle?
 

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Discussion Starter · #3 ·
So it looks like the BMW engine has coil packs instead of wires. I would assume that a faulty coil would result in a constant misfire under acceleration, which I don't have. I can replace the plugs and see if that makes a difference. That being said - there is no notable power loss after the engine is warmed up.

When cold starting the engine; the engine fires right up with no problems at a high idle, then drops back down after a few seconds - this is when the misfire starts (yes, with SES light blinking). No change if the transmission is in gear. This goes away in maybe two minutes.

Wouldn't a dirty throttle body allow the problem to continue after the truck is warmed up?
 

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Sorry- my bad. Thinking of the 4.6 in the other truck.

A dirty TB can do all sorts of things. It's a common issue and the quickest/easiest to check and rule out. In that engine I would definitely suspect plugs at that mileage. And when those plugs go bad, they can sometimes take a coil with them. Even so, many electrical breakdowns begin with thermal related intermittent symptoms. Usually it's the other way around- runs OK cold and acts up warm. But it can definitely go the other way as well.

The easiest thing to do is to get the codes read. A parts store will do this for you for free. Change the plugs and drive it a while. If it goes away, you're good. If not, the code read will tell you what cylinder. At that mileage, I'd just replace the bad coil if that's what it ends up being.
 

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Discussion Starter · #5 ·
I guess I need to get better at including all of the information in the first post.

So here is what I got the other day for codes after the cold start:

P1300
P0301 - Cyl 1 Misfire
P0302 - Cyl 2 Misfire

I will swap plugs over the next couple of days and post the results!
 

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I've owned several MBW's with the M62 engine. Tried several different plugs. Best results with NGK BKR6EK. Should be the exact same plug in the Rover. Although it may be the EIX.

These plugs like to hang up in the holes. if there the originals they might be a tussle. Break them loose and feel for resistance. If they don't come right out loosely, I've found that if you turn them in and out a couple times like an eighth turn, then spray down in the pocket with a good penetrating lube, you'll save a thread. I have a strong preference for a product called Kroil. In the spray can it's called AeroKroil. Expensive, but amazing stuff. Give them a good hour, spraying a few times to get a good soak. When going back in use a copper-based antiseize on the threads. Snug then up well- this engine likes to work plugs loose. Not too tight!

These coils are a 2 piece with a "boot" that connects between the coil and the plug. Your problem could be there, but unlikely. But if you do need to replace parts and put coils on it, replace the boot as well. or if you want to put as few dollars as possible into it, you can move a coil without the boot to another cylinder. If the problem moves, you found your part. Not recommended, but if it's between this and the kid's lunch money...
 

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Discussion Starter · #7 ·
Hi Folks,

So I finally got around to changing out the plugs last weekend.

They did improve the problem significantly, but did not fix it completely. I am still getting a rough idle and multiple cylinder misfire at COLD idle. I pulled my codes this morning:

P1170
P0305 - Cylinder 5 Misfire
P0306 - Cylinder 6 Misfire
P0307 - Cylinder 7 Misfire
P0171 - System Too Lean Bank 1

Note that the cylinder misfires are on different cylinders than when I posted codes last time.

Also, I have had an issue twice in the last month where I turn the key and the engine cranks, but the car does not start. After 5-8 seconds, I turn the key off, then on again and it starts right up. The battery voltage is fine. I have done a little research on this and it looks like my fuel pump could be on its way out. I wonder if this could be contributing or causing the rough idle when cold somehow?

The only other strange thing regarding idle is sometimes the idle will "dip" (almost like a misfire, but not a misfire) about every 20-30 seconds when warm. This only happens every once in a while and barely noticeable.

Thoughts?

Thanks in advance!
 

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Did you return each coil to the plug that you removed it from? The wiring harness could also be deteriorating.

Those problems you describe could be symptoms of a fuel pump. Have you replaced the fuel filter?
 

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Discussion Starter · #9 ·
Yes, each coil was returned to its respective plug.

The harness looked like it was in fantastic shape. The car has lived in Florida its whole life and still has all of the dated LR stickers on the underside of it!

I have not replaced the fuel filter yet. I guess that would be my next logical step. I'll give it a shot this weekend and post my results.
 
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