Alright ive tried looking everywhere for this online and on this site. Cant find anything dealing with naturally aspirated 13b fluttering noise.
Anyways ive noticed it for awhile now but wasnt sure if it was a big deal or not? When im under the hood playing with throttle any time i tap the throttle no matter what rpm it makes this fluttering/rattling noise. It sounds like its coming from the intake.
I have no idea what could cause that but i know that noise it not suppose to be there.
Any help would be greatly appreciated thanks guys!

 

Assuming you have an airpump (you absolutely should on an S5 NA), the pump will make funny noises if the silencer tubing is missing from the ACV. That could be it. It could also just be something rattling around. In which case, you'll just need to look for it.

 

Well when I got the car it didn't have a air pump on it....I started noticing it after a full exhaust installation (cat was clogged) is that a bad thing I don't have an air pump?

 

Yes. Air pump operates aux ports for higher rpm horsepower.

 

I've noticed on other FC's there is an exhaust tube for the air pump if this is needed as well then I have to change my pre silencer on the exhaust.

 

The tube works with the ACV and air pump to help the catalytic converter work.
No cat means you don't need the tube.

On 86-88's, the tube is used to activate the 5/6-ports that marclong is talking about. Your 90 uses pressure from the air pump and a solenoid controlled by the ecu. You want the airpump because it's going to give you a good bump in power when the auxiliary ports and vdi are working properly.

But you aren't doing any damage by not running a pump. You're just down on power from stock.

As for the rattling...It's a 23 year old car that you've been tinkering with. It's going to rattle. Take a long screwdriver and start touching stuff to see if the noise changes.

 

Ok well im got two more questions, I replaced my water pump about a month ago and ended up pulling of the housing as well, after I put it all back together I got a check engine light pulled the code and its the coolant sensor (one behind the thermostat) will this control the accelerated warm up system? Ever since I changed the water pump it has been difficult to start cold and I have had to help it warm up, after which though no more starting problems after warm. My second question is, where is the air supply valve is? im trying to fix my idle under A/C load since it will stall and not idle while on. I have already looked on here for location but I can only find what it does and not where it is. Any help would be much appreciated!!!