I am looking for a diagram of the full intake manifold for an '85 12A.

In trying to sort out the idle issues and having read everything I can find online about all the valves, hoses, switches, etc on this engine I have yet to find a diagram of the complete intake manifold. It seem there are diagrams of the emission bits and other things but was hoping to find an assembly or section drawing. Does such a drawing exist? I was hoping to see what composes the intake assembly before pulling it off the engine.

Yes. I have the Haynes manual.
Yes I have downloaded the FSM from Sgt Fox website.

There are lots diagrams and such but not what I was hoping to see.

The idle problem has an odd sound. The engine will idle at about 1100-1300 rpm. Any lower and it dies. At lower idle there is a consistent change in exhaust sound almost as if something in the intake or exhaust is opening and closing. Seems like a good time to pull the intake assembly and exhaust to clean, repair as needed and install again.

Thanks!

-Mike O.

 

Did you download the carburetor rebuild manual? There are some good diagrams and an exploded view of the entire assembly there.

Checked for vacuum leaks?

 

I have downloaded about everything I can find. There seem to be parts of the whole in the carb manual. Also each of many ancillary pieces in the emissions/fuel system part of the FSM but no cutaway/section or assembly that I can find of the whole manifold assembly.

So far the hoses are in remarkable condition on the car. The only anomaly found in testing is the vacuum side of the shutter valve. It is definitely leaking past the diaphragm. I suppose I should have checked this and other things while the carb was off.

 

I have read through the checklist in the FSM to verify the operation of each vacuum related components. I am thinking that to more quickly isolate what device is introducing the vacuum leak that maybe disconnecting and capping all vacuum (much like the Rat's Nest Delete) is a valid approach.

Of course before that I have to figure out why the instruments are progressively failing and the fuel pump stopped working.

 

Getting back to the idle problem. In the meantime instruments were fixed by removing the pod, re-soldering all components on the circuit board then using a small piece of crocus cloth to polish all contacts. After putting all the screws and nuts back all the gauges work. Well, the fuel gauge tests OK but no signal (or "empty") coming from the sender. That is now on the list. Still haven't figured out why the fuel pump is intermittent.

I've traced the idle problem to two places. The shutter valve is bad; failed diaphragm I am supposing. Also found that the trailing timing vacuum control is not cycling as it should and is leaving the vent side open to vacuum and the breather all the time. Now when at idle with the shutter valve and trailing timing vacuum closed off the idle will run stable at around 1000 RPM. Still a bit high but better than the 1500 we had before. I think we will make a trip to a couple of local yards that have '84 12A cars in inventory and see if we can't get some valves.

It also appears there may be some leakage of the [steel] vacuum piping itself. Found that by accident but maybe we can harvest one from one of the '84 cars. If not I guess it will get a good cleaning and solder the weak areas. Or maybe get some brake line tubing and just bend up replacement sections.

 

These engines being so small, any vacuum leak will wreak havoc on the idle. I chased problems for months, but now they are all fixed and she runs like a champ!

I had a pretty substantial leak on my f150, and it barely made any difference.

 

I appreciate the comment. In general it seems the electrical of the car is OK (except for the fuel pump shutting down occasionally). The vacuum valves seem to be stuck or failed. Hoses are in remarkably good condition but the vacuum hard lines appear to be corroded and weakened. If they are perforated that would add to the issue.