Vacuum Leaks

[dc914guy]

Well, I pulled the motor together this weekend, and cranked it over. My goal was to be out on the road that afternoon driving :-), it’s never that easy!

All of the vacuum hoses are brand new, and properly installed in the car, however when I went to start the car the RPM’s shot up to 3000 as soon as it turned over. I did the typical things, checked hoses, checked around air box with carb cleaner, etc. Later on in the day I was starting to get desperate for an answer, so I tried something radical. With the engine running at 3000RPM’s, I placed a sheet of hard plastic over the throttle body, restricting ALL airflow into the engine, the RPM’s dropped down to 2000 RPM’s and the engine continued to run without skipping a beat !

I’m stuck here, does anyone have any ideas??

~Eric

[Dave at Pelican Parts]

It's obvious that you have a pretty sizeable vacuum leak. Check to make sure that there are no fittings that don't have hoses on them, with the possible exception of the vacuum advance fitting on the distributor (the one pointing away from the distributor body). Also make sure that there is no hose going directly from the air cleaner to the manifold--there should always be some "component" (like the decel valve or the aux air regulator) in the middle.

Plug the large hose going from the air cleaner to the decel valve. If the idle drops, the DV is leaking. Plug the large hose from the air cleaner to the AAR. The idle should drop if the engine is cold--that is what the AAR is, a "programmed" air leak.

Check for leaks where the "manifold boots" (the large rubber hoses between the manifold and the intake runner pipes) are. Check for leaks around the seam of the manifold. Check on the top where the reinforcements are--look for two round dimples in the top of the manifold. Check the bottom of those reinforcements as well if you can.

--DD

[chrisreale]

Timing? TPS switch properly adjusted?

[hardflex]

i'd take each hose attached to the intake air distributor, one at a time, and see if pulling and and blocking the port brings the idle down. do that to all except the one to the MPS, because the car may not run without that one.

i'd suspect either the Aux air regulator or a pcv valve may not be closing.

[Bleyseng]

Timing and vacuum leaks are the supects here. Look at the hose chart here on PP and verify that the hoses are hooked up right.
Or plug all the hoses and openings on the plenum except the MPS and then run it.
Geoff

[John Rogers]

If your throttle body has just 1 vacuum fitting, it goes to the "retard" side of the distributor. Check the distributor to see if the advance weights have the springs attached and will advance and snap back to the retard position. There are very few actual vacuum connections on the intake: the PCV line, the MPS line, the decel valve line and the AAR line (goes in the back). Try clamping each one with pliers to see if one makes a difference. Try feeling the bottom of the plenum with you fingers to see if there is a hole there, our 1974 had a hole in the bottom??!! Good luck.

[dc914guy]

Well I found the problem!!! Long story short, my 16 year old brother has taken an interest in helping me work on the car, he helped me put the injectors in the car, when I went to check them, one of the injectors was seated COMPLETELY OUTSIDE of the hole. And the worst part is it looked fine from the topside!

~Eric

[chrisreale]

That would do it