Idle questions,

[Kaz13]

Hey guys,

I have a '05 4.8is with 120km, and it has an intermittent idle issue.

Here are the symptoms...

-Idles perfectly when cold. No cold start issues, has always turned over first try.

- Once warm, it is still intermittent. When it does idle roughly, there are no RPM changes. Sometimes it idles roughly and is constantly rough, other times it idles with a cycling, "whomp" feel. It feels like it is cycling, and the vibrations varies in its intensity.

-Just tried the A/C and with the AC on it minimizes the vibration.

-In drive , it is slightly more powerful than when in neutral or park, but not completely eliminated.

Wondering if anyone has any ideas on where to start with this issue, based on past experience? I am thinking it is a vacuum leak, due to the cold motor not having the issue.

Do 4.8is motors have a Idle Control Valve? Have not seen a DIY to clean it , and I have searched. Seems the 3L has the ICV, all of the DIYs are based on that motor. I don't not have my bentley manual yet, so sorry if that has been asked before .

Looking forward to contributing and hearing the wise Xoutpost members opinion

Cheers,

[Whitecat]

Originally Posted by Kaz13

Hey guys,

I have a '05 4.8is with 120km, and it has an intermittent idle issue.

Here are the symptoms...

-Idles perfectly when cold. No cold start issues, has always turned over first try.

- Once warm, it is still intermittent. When it does idle roughly, there are no RPM changes. Sometimes it idles roughly and is constantly rough, other times it idles with a cycling, "whomp" feel. It feels like it is cycling, and the vibrations varies in its intensity.

-Just tried the A/C and with the AC on it minimizes the vibration.

-In drive , it is slightly more powerful than when in neutral or park, but not completely eliminated.

Wondering if anyone has any ideas on where to start with this issue, based on past experience? I am thinking it is a vacuum leak, due to the cold motor not having the issue.

Do 4.8is motors have a Idle Control Valve? Have not seen a DIY to clean it , and I have searched. Seems the 3L has the ICV, all of the DIYs are based on that motor. I don't not have my bentley manual yet, so sorry if that has been asked before .

Looking forward to contributing and hearing the wise Xoutpost members opinion

Cheers,

I have similar problem, Check if you have leaks (valve cover gasket, cam Sensor there is 4) spark plug may need to be changed .....you need to get the code to see what it says.

[racingbmwm3]

4.8 (N62) does not have an idle control valve. You have valvetronic instead. If you aren't finding an answer searching here, look on the E60 and E65 forums for your symptoms. Or try the E70 forum also.
Guesses: CCV's going bad, MAF needs to be cleaned, air filter is dirty/clogged, dirty/clogged injectors, fuel pressure regulator having issues. Other ideas I have would also cause a check engine light, these are the only ones I can think of that could cause rough running without the check engine light. Scan the DME to see if there are any faults (pending, present, historical).

Bad gas? Carbon buildup? What's your typical drive cycle? Fill up with some good quality premium fuel, throw in a bottle of Techron concentrate and go for a couple hour drive on the highway. If that fixes it, it was just bad gas or dirty injectors.

You are very lucky to have a car with only 120kilometers on it. Unless you mean 120,000km. Bad gas? Carbon buildup? What's your typical drive cycle? Fill up with some good quality premium fuel, throw in a bottle of Techron concentrate and go for a couple hour drive on the highway.

[Kaz13]

OK great thanks for the info guys!

No check engine lights... No codes. Idle is also intermittent. Im still leaning towards vacuum leak... I have tried starter fluid around the gaskets to no avail.

I use 94 octane chevron with some added techron, but I cannot buy that stuff in Vancouver anywhere... They used to sell it at the Chevrons up here, but not any I have looked at.

I wish it was 120km, it is in fact 120000kms.

Just checked the CCV's yesterday. Seemed fine, no cracks, and no splits. Is there any reason to change them, or is the diaphragm the only thing that fails on those?

I have checked the air filter, it is clean.

Thanks for the updates, I will continue to document my findings to help others who will find this post down the road!

Cheers,

[racingbmwm3]

Should be able to buy the concentrated form of Techron at any parts store. The BMW dealer also sells bottled of the fuel cleaner (says BMW instead of Techron on it, but its the same thing).

AFAIK, if the diaphragm is ok, the CCV is ok. If you can monitor the engine adaptation values that would give a hint if there is a vacuum leak or not.

If you do lots of short trips, I'd still bet on carbon buildup or dirty injectors.

[Kaz13]

Yep I've tried all the usual canadian suspects for the Techron, but they do not sell it anywhere Ive seen. I had an old maxima and that stuff worked great on it so I will try to track some down today. Worse case I can go sped 45$ on a bottle at the Dealer. :/

And yes I unfortunately do lots of small trips. I run my own business and my distributors are rather close by {Within 4 KM of the shop} so there are lots of small trips.

Does cleaning carbon buildup just require longer drives?

[racingbmwm3]

Ouch!! $45?? Another one I haven't tried is the stuff from Liqui-moly, I think its called Ventil Sauber, they also make something called Jectron.


Yes, I recommend driving to Kamloops via 99 at least once a month or more That will keep your engine clean and burn off any extra deposits that are lingering around. I recommend using Sport or Manual mode from Pemberton to Lilloet.

[Kaz13]

Haha thanks! Very specific directions! I have 0 reasons to travel to Lilloet however!

I did just put over 200km on it picking up some equipment in Abbotsford, and those were all highway KM at about 130km/hr .

Ill try the BMW cleaner and see what that does for me, Thanks for the inputs!

Also thinking about changing the plugs. Not a lot of cash and I doubt the previous owner did it. Hopefully its something simple like that!

[racingbmwm3]

I also doubt the plugs have been changed yet. Plugs should only need to be changed every 160,000km, but with lots of short trips 100,000km could be justifiable.