Originally Posted by dannyk304

I am 99% sure this is caused by your throttle body/valve. I had the same issue when I bought my 991.1, it was always associated with a slight roughness in idle as well. I tried chasing the idle stability with various changes, even asked a shop to listen to the noise as the momentary roughness in idle always went along with the noise similar to yours, and no one had anything of value to add. A year later I stumbled on a post somewhere complaining about a similar noise (they called it a frog - and mine sounded more frog-like as well) and changed my TB and low and behold, the noise completely gone and idle rock steady ever since - a year on now and no issues. Good news, it's under $200 From FCP Euro if you buy the Bosche OEM product and it was very easy to install in my garage. Good luck and if you do it please confirm this worked.

Originally Posted by Jonny9999991

Thanks for your reply, your situation sounds just like mine! Rough idle, apparently was an o2 sensor but now got this frog/dog!

Will let you know how it goes, thanks again.

Originally Posted by dannyk304

I changed plugs, coils, PCV hose (that had slight crack, VVT solenoids, MAF, camshaft position sensors, air filters, and other things all to no avail. This TB change was magnificent for me.Good luck and let me know if you need any info on changing it. was rather easy compared to the other things.

Originally Posted by rensoyka

could also be drive belt or tensioner problem. anywhere else where there is a bearing for something rotating, alternator, water pump, a/c compressor.

Originally Posted by Jonny9999991

thanks do you have a part no for the 991.1 c4s? I’m getting two sizes, a 72mm and 84mm iirc.

Originally Posted by dannyk304

Hi - I believe it's an 82 MM - and that is the only size for all 991.1 cars. Previously, 997 used a smaller bore but in the 991 they've all been upgraded and all one size. The part number is 99760511601 and in FCP Euro you'll find it under BOS-0280750473.

Originally Posted by Southbranch

Very interesting. I occasionally hear that noise from my 2016 GTS when I'm back in the garage after a drive on a warm day. I thought it might be emission control related but haven't yet investigated it. I do see from a couple of parts websites that the throttle body part number may not fit the GTS. Other sites say it does fit.

Originally Posted by Jonny9999991

funny thing is mine started intermittent, now it’s every time I turn on

Originally Posted by Viper1000

Does it impact drivability or is it just more of an annoyance? Are you able to hear it while driving?