Thermo valve in 1988 911 Turbo

[DP935CAB]

Can someone tell me if the thermo valve(brass threaded plug with 2 vacuum lines attached to it) is suppose to be open when cold or closed and which side of the distributer pot it is connected to, advance(farthest from the distributer) or retard(closest to the distributer). It seems like if closed when cold it would have to be hooked up to the retard side so the engine would idle up for the start, but mine is hooked up to the advance side and I believe the schematic also shows it hooked to the advanced side also. Can anyone shed some light on how it is hooked up and its operation? Thank you......

[TurboBert]

The thermo valve connects to the distributor pot closest to the rear of the car (its the tube that is most visible).

It's closed on a cold engine. It takes 15 to 20 seconds to open after you start the car. When it opens, it allows a vacuum to retard the ignition 15 degrees.

[DP935CAB]

Thats what puzzles me. The side closest to the rear of the car seems to advance the timing and increase the idle. With the car running I put a hose on it and applied vacuum and the idle increases. Do I have it backwards? Does the idle increase when the timing is retarded and decrease when the timing is advanced?
I pulled out the thermo valve because the car would only idle at 850 rpms on a cold start and then slowly increase to 1000rpms when warmed up. I replaced the aux. air valve and no change. The thermo valve was closed and the only way to get it to open was using a torch and heating it up until it was almost to hot to handle. It seems it should open up quicker than that. Help....
Thanks.....

[DP935CAB]

One other thing I don't understand is, if the thermo valve opens when the engine gets hot and applies vacuum to the advance side of the distributer pot, how would the the timing retard at full load if the same amount of vacuum is applied to the advance and retard sides of the distributer? I have one vacuum line from the retard side going directly to the throttle body and the other vacuum line from the advance side to the thermo valve and then to the throttle body. Thanks again....

[TurboRuf]

DP935,

Lots of information on this in the archives...

Try:
Any 930 Turbo Owner.. Please Read!

...or doing a search on Thermo Valve.

[DP935CAB]

Thanks, I read that post and all the others and it is still unclear to me which vacuum line is retard and which one is advance. The post says the inner one closest to the distributer is advance but when I connected a hose to the other port facing the rear of the car and created suction, the idle increased leading me to believe that one is the advance port. If the thermo valve is suppose to be closed when cold I would tend to think it would be connected to the retard side so you get the retarded timing when under load when the engine is hot, but that would mean the advance side would have vacuum all the time being connected to the throttle body if I were to switch the lines. I'm still confused...

[TurboRuf]

I think it depends on the vehicle year, but the front upper port on the canister should be advance and the rear lower, backside, should be retard.

The front upper port connects to the Thermo Valve then back to the upper right side of the throttle body. This is the red vacuum hose shown in the link above. The Thermo Valve opens as the engine warms up. The lower rear should connect to the upper left side of the throttle body.

Hope that helps...

[DP935CAB]

Ok, this is the way my car is hooked up. But if the advance line is connected to the thermo valve and the thermo valve is closed until the motor warms up, that means the distributer is retarded until the thermo valve opens up and vacuum at that point would advance the distributer. The retard line is hooked, as you mentioned, directly to the throttle body and would have vacuum all the time. I thought the distributer would be advanced for start with a higher idle until the motor warms up? It seems to me like the 2 lines at the distributer are reversed. I would think you would want to block retard, and when the thermo valve opens, the idle would fall due to vacuum. Its confusing because the earlier cars had the therm valve hooked to the warm up regulater. I believe from 1985 onwards they went with the heat operated threaded plug with the 2 vacuum nipples. Great discussion. Any other ideas?