1991 US Testarossa

you may have a look in the WSM please

 

There isn't a good single figure for this IMO -- even in the TR WSM, they mangled things a bit.

For the US TR vacuum lines:

1. There is a single small vacuum fitting on the front end of the 1-6 intake manifold plenum -- this supplies vacuum to the differential pressure switch and to the electrovalve for the air injection system. See Fig 53 of the air injection system on page 72 of the TR OM 634/90.

2. There are two small vacuum fittings on the front end of the 7-12 intake manifold plenum -- one goes to the Microplex ignition ECU over the LH rear wheel well; the other goes to the vacuum reservoir for the AC pushbuttons over/at the back end of the LH rear wheel well.

3. There is a single small vacuum fitting at the rear of the 1-6 intake manifold plenum -- this goes to one of the charcoal canisters behind the RH rear wheel well. See Fig 57 on page 77 of the TR OM.

4. There is a single small vacuum fitting at the rear of the 7-12 intake manifold plenum -- this goes to the other charcoal canister behind the RH rear wheel well; and a large vacuum fitting that goes to the brake booster.

For other air lines, see Fig 48 on page 67 of the TR OM or Fig 49 on page D68 of the TR WSM -- both correctly show the large air lines going from the bottom of the airflow metering units to the AAVs and then on to the fittings on the intake manifold plenums where the cold start injectors mount. What they mangled is that both of these figures wrongly show bypass valves (aka vacuum limiting valves), item 16, and their associated plumbing which are not used on US version TR.

With all that said, unless there is some very serious error somewhere, it shouldn't prevent you from being able to adjust idle -- can you be more specific about the trouble you are having adjusting idle?

 

None of that sounds too good. Are you saying that if you unplug the O2 sensors wire single output wires (label things before unplugging!), forcing open-loop operation, then the warm idle is smooth (even if the power is down)? People often (wrongly) remove the differential pressure switch when they remove/disable the air injection system, but this would only affect acceleration during cold-running. Even if a lot of things are wrong with the vacuum system, getting a smooth warm idle should still be possible. Can you indicate:

1. What elevation above sea level are you at (i.e., what is the typical barometric pressure)?

2. What are the vacuum levels in the intake plenums when you are at 1000 RPM warm idle?

The Microplex ECU uses this vacuum level to determine the engine load and then sets the ignition timing based on this load and engine RPM. See page D63 in the TR WSM (or page D5 for another example, but not really for the US version TR) -- this is the ignition map for the Microplex ECU. If you have no vacuum hose going to the Microplex ECU, the vacuum level "A" would be 0 millibars = the curve "1" in the graph would be used. This would retard the ignition timing a little at idle, some at mid RPM, and a lot at high RPM. This would make the engine feel sluggish, but idle should still be smooth.