1981 911 SC Vac Hose Routing

[Rick Dreher]

Hi Gang,
First time here. I have an 81 911 SC that was running like a champ but had vac leaks at the intake runner boots from 214k miles and age. I dropped the engine and replaced the boots and gaskets. O rings at the injectors, air box gasket,and anything that looked like it was a potential oil or air leaker. Car starts right up cold and idles down and runs great driving but failed smog for high CO and high HC. I may have my vac hoses to the advance and retard part of my distributor backwards or have the deceleration vac hose plugged in the wrong port. The car passed smog fine before I dropped the engine so I know I screwed something up. The temp gauge barely moves and does not move into the normal range. After driving the car on the freeway for 1/2 hour and then into local traffic the engine will race and not idle down although the throttle plate seems closed (off the gas pedal). If I shut the car off and restart, it starts and idles fine. It takes the heat soak of freeway to make this problem occur but yet the temp gauge seems to stay low. I have an infra-red temp gun and would like to know where a good place to shoot it would be to check the operating temp. I have a 75 anniversary 911S that runs great but the 2.7 hoses are different than the 3.0. The 2.7 only has one hose to the distributor and no deceleration valve so referencing ol faithful helps me none

[L8apex32]

The "engine will race" after highway use issue is the larger issue, I'd think, and you should start there.

As far as vacuum lines to the WUR and distributor, in both cases, the vacuum at low RPM conditions allows the car to run in a more eco friendly manner. For the WUR, it raises control pressure and for the distributor, it retards the timing. (At open throttle conditions, there is less vacuum and the WUR goes to more rich and the distributor goes to more advance.)

These don't have anything to do with "engine racing at idle" as far as I know, although they certainly could affect your emissions problem.

The AAR is a simple "when hot is closed" device so, while it controls air and could lead to racing... it doesn't seem likely. You could take it off, heat it up and see how closed the valve goes. It should go fully closed when "warm" and stay closed when hot. Maybe yours goes past closed to open somehow? Doesn't make sense to me.

Engine "racing" requires too much air getting in so start with "air getting in" causes.

The fact that the problem stops after a stop/start procedure doesn't make sense to me, but I have a euro so I don't have lambda/frequency valve. I'm sure others will have better ideas.