Vacuum testing to diagnose fast idle

[alexiskai]

OK, we are back to discuss my fast idle problem in a clean new thread. Previous thread is here. At the end of that thread, it was recommended that I attach a vacuum gauge to help diagnose the problem.

I'm going to start by describing how I set up the vacuum test, because it took me about a week to get all the parts together. The pictures attached here show the individual parts and then what they look like fully assembled.

The vacuum port in most intake manifolds uses a 3/8-fine thread. A vacuum gauge that you can buy in an auto parts store uses a barbed fitting. The challenge is to mate the two. I was able to find the brass fittings I needed in the plumbing section of Home Depot, but it was a challenge because the measuring convention is different (plumbing measures the internal diameter, automotive measures the external) and they didn't have exactly the right adapter.

What you see here is:

• Vacuum gauge from O'Reilly Auto Parts
• 1/8" brass hex nipple - this fits the intake manifold
• 1/4" female to 1/8" female coupling
• 3/16" barb to 1/4" male adapter

If you can find a 3/16" barb to 1/8" male adapter, that would also work, but I couldn't find that so I had to use an intermediate coupling to reduce the size.

Second picture shows what it all looks like fitted together and ready to go on the car.