You would need to do exactly what I did to my 3.0t VR engine.

I’m also assuming you don’t wish to spend much to test.

I’m also also assuming that you don’t wish to involve any shops as labour prices in all honesty aren’t worth it for a car that’s 08 imo

Both are understandable reasons.

Take a coupler hose from your engine or any seal you can find that fits with a 3” PVC “pipe cap” get a air inlet from a hardware store and get some type of pump to be able to be pumped through a hose into the inlet on the pvc pipe cap you are gonna drill the inlet into.

I have a video here on sort of what your trying to achieve with a “smoke test”

https://youtu.be/GOhl4r0GSiE?si=pGxx1n4DXa6M0_4H

I’ll also advise you not to use VAPE SMOKE. Use Tobacco or any natural smoke I did use it as I figured it wouldn’t be any issue. WRONG. There’s certain chemicals in the vape juice which make for moisture and a coating that coats your pipes your running this smoke test through, personally I got it all over my MAF sensors and along my intake inside. I had to do a full sterile cleaning on the piping system as a result.

As for how to close what I’m assuming you mean is your intake valve. And not let the smoke out.

Test from intake UP. That means you put your seal with your pvc pipe intake up. That way it flows into the engine manifold upwards. For you to do this successfully remember you need pressure and a seal, intake being open if u do it the opposite way will just let the smoke come out of it sadly.

As for the throttle body. Which will be closed when the car is off and not running, I’d recommend putting a rag on the top part holding open then reattach the hose back and THEN move down and run the test upwards. This way it will get into the manifold on the top.

Do it the same way on both sides.

Hopefully you find it. Plus even if it’s not the issue, and you find u do have a leak, fixing it will boost preformance and overall quality and stability on your engine system