AO

I mean the throttle position switch - specifically the idle conact. I'm sorry I don't know exactly where it is located on an 85, but you should hear a distinct "click" when the throttle returns to idle. If you hear it, then you need to check at the LH to ensure you're getting the signal there. If no click... you may need to adjust the throttle cable or replace the switch.

Dan87951

Does the car have to be running to hear this click?

AO

No... in fact, it would be near impossible to hear it while running.

Jim bailey - 928 International

there is a throttle position switch mounted to the butterfly shaft way down under the intake. part # 928 606 157 00 throttle-valve switch in Porschespeak. The switch however when the idle speed contact has an open failure there is no fuel cut off during coasting but the car runs O K , if the full load contact shorts the car goes over rich and burns a lot more gas. However if the idle speed contact has a short (constant contact) it will cut out at high idle speed.

Jim bailey - 928 International

If the temp ll sensor is unplugged ( infinite ohms ) the car goes excessively rich and will not run when warm.

Dan87951

Isn't the temp II the one that is connected on the water bridge? If so that one is hooked up. The one on the front of the intake manifold is not. I will post a picture later tonight clarify. Honestly we don't know what goes there, there is a threaded hole like a sensor plugs in and I have two more wires so I figure something goes there?

cold_beer839

Cheapo Test: Pull the vac line off the brake booster and plug it with your finger tip and see if the engine will idle better. If it does, your brake booster is bad (as long as you KNOW the line is good).

Jim bailey - 928 International

Correct temp II is on the crossover thermostat housing ..what year car are you working on ??

Adam Geist

If the car you're working on is an '85/'86, the sensor mounted horizontally in the front intake tube (above the water bridge) is the intake temp sensor for the condenser fan. This sensor is wired through a resistor and runs the fans at a lower speed if the under the hood temps are high when the engine is turned off and the key is out of the ignition.

This is not the same as the condenser temp switch mounted in the driver's side radiator tank that turns the condenser fan based upon coolant temps.

The TPS switch is mounted on the passenger-side of the throttle body. There is a short wiring harness with a 3-pin connector on each end that connects the TPS to the main harness. If this is disconnected, expect the engine not to run properly at idle and above idle.

If the vacuum system and TPS check out OK, I suggest you check the ISV as well.

Dan87951

Update:

First problem is solved. The car idles on its own now. The problem ended up being one of the intake hoses that hold the intake end caps on was flopped in. However my second problem is still there. The brake booster does not seem to be working. All the vacuum lines are hooked up properly and there is plenty of fluid in there. When I disconnect one of the lines from the booster it does not make a difference in how the car idles. Also I do not feel any suction on the vacuum line at all.

Below are the pictures hopefully they help? The car I'm working on is a 1985 928S.

Dan87951

Also want to mention that I cannot press the brake pedal to the floor its stops about 3" down and is hard like a rock. Maybe a stuck caliper?

My stupid self was messing with the check valve and broke the thing from the 4 way T and also where it connects to the nipple which I believe is on the booster? Why are the 4 way T's stupid money? Is there aftermarket source that is cheaper? Can I fix the nipple part as well?

Dan87951

Did some searching sounds like a brake booster might be bad? Is this common from the car sitting for so long? When I have my foot on the brake and start the car there is no difference in pedal feel.

Jim bailey - 928 International

The larger braided cover hose MUST be showing vacuum or the booster has NOTHING to boost with...find some vacuum ! The parts prices are what they are because Porsche management and owners (Porsche and Pieche families ) take great pride in being the "most profitable car company" . The annual report makes that very clear

ew928

Brakes are vacuum assisted.
When my vacuum check valve went flakey, I lost brake boost and the pedal was really hard to push with little corresponding braking.

Back to chasing for the missing vac.