*Video included* Weird behavior of '08 3.0si naturally aspirated engine

autoque · #1 10-30-2012, 05:30 PM

video-2012-01-25-00-12-22 - YouTube

Only when the engine is warm does this happen. Around 00:16 seconds, you can see the rpm needle rise up a few hundred rpms only to go down again after a couple of seconds. It does this almost everytime when the engine is warm (usually when it had been used an hour or two before).

How about others with the 3.0si engine?

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zx45 · #2 10-31-2012, 04:51 PM

Whats wrong i've watch the video twice, no big deal..

rh71 · #3 10-31-2012, 05:34 PM

non-issue

autoque · #4 10-31-2012, 09:44 PM

Thanks for the replies!

What I forgot to mention is that it does this every single time like a ritual on warm starts. Do yours do this too?

rh71, I know for sure you have the 3.0si. How about yours? Does the rpm go up like mine on warm starts?

I'm trying to locate the source of an issue with an engine by the process of elimination and I'd like to rule this one out as a symptom.

Thanks.

jeremym · #5 10-31-2012, 09:56 PM

Just a data point, might not matter, my 4.8i does NOT do this. When it starts and ambient temp is cold, it will hover around 1k RPM until fluids are moving and then settle to 500-600 rpm. Or, if I put it in drive while it's idling at 1k rpm, it will drop to normal idle.

However, after dropping to normal idle (even still in park), it does not jump back up.

autoque · #6 11-01-2012, 10:03 AM

Quote:

Originally Posted by jeremym

Just a data point, might not matter, my 4.8i does NOT do this. When it starts and ambient temp is cold, it will hover around 1k RPM until fluids are moving and then settle to 500-600 rpm. Or, if I put it in drive while it's idling at 1k rpm, it will drop to normal idle.

However, after dropping to normal idle (even still in park), it does not jump back up.

Yeah, this is the behavior I expect from most, if not all, engines. And if I remember correctly, my 3.0 used to be normal like this. But it started to behave weirdly after cylinder head replacement.

jlam86 · #7 11-01-2012, 05:43 PM

Is your ac on? Maybe that is cycling?

autoque · #8 11-01-2012, 08:10 PM

Nope, AC not on.

jlam86 · #9 11-01-2012, 09:39 PM

what about the front defrost cycle? that triggers the AC compressor to go on as well I believe.

CarsRmyVICE · #10 11-01-2012, 10:04 PM

That's nothing you should see what my 50i does sometimes. I will start it and it will shoot up to 1500 plus and bounce around for 10 seconds. My mom has a 328 and even her car idles funny on occasion when I am at stop lights etc. My service rep blames it on stale 91/93 gas. Claims people aren't buying as much because of the economy and tells me to use 89 since it is fresher lol FWIW our last two bimmers did none of the sort.

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