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Unsteady Idle

 
Old 04-25-2018, 04:58 PM
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Dmitri
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Default Unsteady Idle

My 2009 997.2S has just under 104k on the clock. During the past several months, the car has been idling funny, especially when the engine is cold on the fiirst start of the day.

After start-up, the idle settles in at 700, but then “hunts” between 600-800. Once everything is up to temp (~180 oil and 175 water), things seem to calm down. if I did this correctly, there should be a video attached.

This is is a new behavior for this car. Previously, the idle was pretty steady at 700 no matter what the engine temp.

I had had it checked out at the dealer and they found no codes and said everything checked out fine on paper. They said they were aware of some similar issues that might be fixed with a software update. They also mentioned that this could be an early indication that something was going to go wrong with the PDK transmission.

We did the update. This morning, same thing. Anyone have a similar experience/thoughts?

Thanks!

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Old 04-25-2018, 05:06 PM
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Bruce In Philly
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2009 C2S 124K miles

It is usually a dirty throttle body.... very common. Google throttle body cleaning 997. Remove the whole aribox and remove the hose clamp at the throttle body. I purchased a can of cleaner, spray it on a rag, drape over a screwdriver, and jam the rag in there. Spray on and wipe the butterfly.

If you see wet oil in there, you may have a failing air-oil separator. For me, the rag comes out black. I do this as regular maintenance when I change air filters.

Getting the hose back on the throttle body is tricky as there are internal nubs in the hose. Check out my video below where I show you the nubs.

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Run ahead to :48 for the nubs
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Old 04-25-2018, 05:09 PM
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Dmitri
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Thanks, Bruce. The dealer said there was a slight carbon build-up on the throttle body, which they cleaned. They don’t think it’s sticking. I will talk to the mechanic to get more details about what else he found there.
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Old 04-25-2018, 05:10 PM
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Bruce In Philly
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Originally Posted by Dmitri View Post
Thanks, Bruce. The dealer said there was a slight carbon build-up on the throttle body, which they cleaned. They don’t think it’s sticking. I will talk to the mechanic to get more details about what else he found there.
I have no idea why a dirty butterfly would cause a bouncy idle, but it does.

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Old 04-25-2018, 05:23 PM
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millertimefl
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I had the exact same issue and went down the same dealer road where they found nothing wrong. I suggested the throttle body itself being bad because I could hear a strange metallic flapping noise from it at idle. Sure enough they happened to have the same year 911 (2010 C4S) in the bay next to mine and they swapped throttle bodies and it idled perfectly. Swapped with new one and perfect ever since. Try holding the throttle perfectly still in 1st or 2nd gear and see if you can feel the same variation in throttle while driving. What happens is that the gear/motor mechanism that controls the intake flap wears out and there is this weird play in it and it flaps around in there causing the hunting symptom.
One of the rare cases where I should have just hit up Ebay and bought a used TB to test my hypothesis which would have saved me time and money and if it didn't help just sell it.
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Old 04-25-2018, 05:26 PM
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104k miles on the 997.2 PDK? I haven't heard of higher mileage than that on PDK. neat.
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Old 04-26-2018, 02:26 PM
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voiceprint1
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any other member do a throttle body swap with good results on idle?
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Old 04-26-2018, 06:02 PM
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OnlineAlias
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Originally Posted by Bruce In Philly View Post
I have no idea why a dirty butterfly would cause a bouncy idle, but it does.

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Because it causes the throttle body to have an inconsistent "zero" setting. Basically this causes a mismatch between the amount of air coming in and what the computer thinks should be coming in. Standard Bosch systems require that after you clean the throttle body, it should be re-zero'd in the computer.
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Old 04-26-2018, 06:44 PM
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larrysb
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How smooth should the idle be on a 997.2S engine? I bought mine used and it's had a bumpy idle, maybe up and down 50rpm since I bought it. Wasn't sure if it was normal or if cleaning the throttle body is needed.
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Old 04-27-2018, 12:52 AM
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This can also be caused by a faulty or on the way out MAF (air flow) sensor. The easy way to check this is to remove the electrical connector at which point the ECU reverts to a default generic map. If idling is then smooth you should replace the MAF. Simples
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Old 05-25-2018, 04:51 PM
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Dmitri
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Well, since having the software update, I’m still experiencing a bouncy idle. In fact, it seems worse. It used to do this only on a cold start and settle down after the engine oil came to temp. Now, it seems to do it a fair amount of the time.

During a recent episode, I popped the engine cover to listen closer. When the throttle is dipping, there’s a metallic rattling sound. I shot a video that, hopefully, I mangaged to attach.

Its back lack to the dealer next week. In the meantime, if anyone has an idea about what this is, I’d appreciate it.

Thanks!

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