Here's the story: 2005 G35 coupe, 125k on the clock, Amsoil synthetic oil, not driven hard, premium gas, no mods other than a K&N filter. I can let the car idle and it is smooth, no rpm blips or anything. Recently I was driving down the interstate and I had to pass a driver. My cruising speed was about 75 and to get around him I had to punch it to 90 and THEN the sound. When the car drops back to 70-80 it disappears. Later I checked the oil level, OK, ran an engine scan and no codes. My first thought was that it was a timing chain issue but if so that rattle would be noticeable at speeds under 90 also and cause the POO11 camshaft timing code.

If I never got the car over 80 I would never even know this was happening. I know changing the chains is not in my DIY wheelhouse (and probably not the problem since they are good for the life of the engine generally) so any insights as to what is happening I would appreciate. If there is a broken guide or something, then if you have experienced this, I would appreciate an idea of how much it might cost me.

 

Well...

Don't drive over 90 anymore ...

But a video would help explain this because I can't figure you out.

 

You can't figure it or me? At 90 MPH it sounded like something was loose, like a timing chain, maybe the tensioner. It's not knocking and pinging and of course nothing major (I figure) since there are no codes, sluggishness or smoke from the exhaust. I am thinking the timing chain tensioner is going bad, becoming apparent when engine speed increases and RPMs. I don't need to drive 90 but I would like that option to do so, rattle-free if need be.

 

By the way, the sound is what you would think you'd hear if you were running a car oil starved and the valvetrain was letting you know it. But as I said, oil levels are fine and driving in the city and highway cruise speeds, no sound and nothing at idle. I see some posts that suggest valve timing solenoids being bad but no code=no problem as far as the PCM is concerned.

 

Put it in manual mode and keep the gear locked in 1st to get the rpms up at a lower speed, if the issue persists and can be isolated as being related to RPM only and not actual vehicle speed then I would first start looking at the exhaust components to see if something is worn.

If you can reproduce the issue with the vehicle parked by just revving the engine then it will be even easier to locate.

 

My car is a 6MT so I don't know if that applies but thanks for the input.

 

Well that's even easier, can you reproduce the issue in neutral or 1st gear? When it happens do you feel any vibration or sudden loss of power? It could be something as simple as the undercarriage cover isn't fully bolted down at once you hit a certain speed it starts to flap like crazy. If you can reproduce the issue at a lower speed and find it's related to rpm rather than vehicle speed it might be something entirely different.

 

I will get on that ASAP, thanks.