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Discussion Starter #1
My fellow OG's...that loud cold start that we all enjoy (short as it may be) on my 12 LP550 is no more. I noticed for the last 4-5 starts that cold starts are very tame sounding and the idle is slightly uneven for a few minutes until it warms up a bit. I suspect a defective coolant temp sensor but I can't find any inherent symptoms for this anywhere... can't even pinpoint the temp sensor location. Any ideas, similar experience?
 

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Your exhaust solve might be stuck on quiet. There is also a vacuum hose to control that valve which may be loose
 

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The loud start is caused by the air pumps not by the valves, ironically enough. Do you have any warning lights or anything? The pumps are emissions related so I’d assume they are heavily “sensored” and that you would have a light popping up or a CEL if something was wrong. Is the temperature sensor ok?
 

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The loud start is caused by the air pumps not by the valves, ironically enough. Do you have any warning lights or anything? The pumps are emissions related so I’d assume they are heavily “sensored” and that you would have a light popping up or a CEL if something was wrong. Is the temperature sensor ok?
That's the strange thing... no CEL. Cold start idle is a little uneven but revs without hesitation. I'm guessing mixture control issue, maybe coolant temp sensor signal incorrect thus incorrect startup mapping and no air pump activation... but signal not completely out of range so no check engine light.

I thought for sure someone would have experienced this. I guess I just have to scan it for codes and clues. Any idea where the temp sensor is? Couldn't find it online.
 

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Interesting subject because I've often wanted to start my G in 'stealth' mode!

My understanding is that the noise on cold start is due to a combination of increased idle speed and also change in cam-timing.

If you're not getting the cold-start idle speed of around 1200rpm, that's at least one of the two. As the ecu speed is electronically controlled, it could be a symptom, e.g. ECU decides not to raise engine speed due to lack of oil or fuel pressure.
 

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Maybe the airflow meters need replacement or cleaning. However when it happens your revs are not stable...
 
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