So the 73 2.0 I bought has no AAR

I have got it running and it starts almost immediately and slowly builds idle speed to around 1500-1750.

I will have to pass an emissions test, and of course, this is likely too high to pass the first time. Rumor has it, the previous owner couldn't get it to pass either (before it sat for 13 years).

So... it obviously runs without it, lines have been capped. The cold start valve end is capped too.

I did the "spray starting fluid about and listen for differences" and think that I may also have a leak by the intake manifold (just at the plenum, below the throttle body) on the passenger (right/battery) side.

I discovered this missing component (no circuit to a decel valve either). I think I do have the MPS (only one hose)

Also, there is only a vacuum line at the back of the distributor... instead of both sides. The front is capped. The additional input into the plenum is capped.

Questions/Advice:

So is there a replacement part, or do I need used?
Is it really necessary, or just a nice thing to have (meaning can it idle properly without it?)?
I have read the decel valve is not needed.

Is emissions really required? Quick google search says in Colorado it's for vehicles 1982 and newer, but admittedly I didn't do detailed analysis.

High idle is normally caused by vacuum leak or timing too far advanced.

Hard to know exactly what a PO did or did not do, but some distributors only used the retard vacuum line, not the advance, and at one point Porsche did away with advance on the distributor.

The retard line is supposed to help with emissions at idle. That's most likely what you have. If you don't have that attached properly to distributor you will get a high idle (your advance will be too high at idle). The vacuum advance was intended to help with transition acceleration from idle. It's not really necessary, and many of us don't have that. So review how those are hooked up (or not) to your throttle body. If you don't have the advance hose, cap it at the throttle body but NOT at the distributor.



Yes, MPS has one hose. Decel is not strictly necessary for car to run, but it protects your MPS from blowing the diaphragm on very high engine vacuum (high overrun or backfire or something). That cap on plenum was probably for the Decel valve.

Some good reading and resources:

https://bowlsby.net/914/Classic/TechNotebook.htm

https://members.rennlist.com/pbanders/DJetParts.htm

EDIT: I should add, you're going to want the AAR. Once you get all your vacuum stuff sorted out, you'll get pretty lousy cold start/performance without it. Put a WTB in the classifieds.

Thanks for the reply and links.

It was in reviewing those that I determined I was missing components.

The emissions check (2 speed Idle test) is the variation I have to pass as it is a transfer of ownership, necessary for title and plates. The car was not running when I bought her.

I am sourcing a AAR.

I will try to get the leaks found and addressed in the mean time. I have my suspects at on the right side of the plenum.

I misunderstood when I looked at the emissions site.

As she is a 73, (older than 75) in Larimer county, CO... I can simply request collector plates and not be tested. This was pointed out to me at the testing area by the tech. I excused myself from line and drove home.

Just adding this back to the conversation to possibly help another owner in the future.

Thanks again!

If you have two ports on your stock dizzy and the diaphram is good (check it) the dizzy advance will not work correctly with a cap on it.

My best advice is to put all the stock parts back on with known good components.

Sounds like you created a Vacuum leak. Start capping everything off. You will find with out a AAR you car will idle too slow at start up and konk out. Once it is warmed up it can idle properly.

That is what I am doing...

I replaced the injector seals, and my RPM dropped a little.

But she is still a little higher than the spec (1250).

I have replacement set of vacuum lines coming as well. I'll find the leak.

It is common to have the intake manifold under the the throttle body to form cracks. You mentioned there was a leak near the throttle body so I would start there.

It is also worth looking at teh bottom of the plenum for rust holes.

I have 1 plenum in my shed with rust holes in it and I have seen several others.

Not normally a problem for a car that is driven regularly but if it has been sitting for years, a little moisture can start the rust growing.

Jim