Vacuum leak under the fuel distributor

[bfloyd]

Help me pinpoint a supposed vacuum leak.

My car has always had a high idle since got it running last summer. Not that big of deal, as it's just another annoying thing on my list of things to work on on the car.

Cruising down the highway, the engine performs like a dream, however starting from a dead stop at a red light, I'm always the last to get through. It hesitates a little, sputters a little bit and then takes off.

I found a mechanic that works solely on European cars, and was familiar with the K-JETRONIC fuel injection system so I took the car to him to get my fuel air mixture ratio set correctly. He did a vacuum leak smoke test and told me there was smoke coming from somewhere under the fuel distributor. Would I be correct in assuming that it's probably coming from the air mixture unit, and more particularly the connection between the air mixture unit and the auxiliary air pipe?

I've got all new silicone vacuum hoses run to everything, so surely it wouldn't be that?

Where else could leak down there?

[sdg3205]

Yes, quite possibly. You can use a good flashlight too - take off the air filter box, shine the light down around the idle speed motor and push in the metering plate and look for light on the left where the POA enters. If you see light, you have a leak. There are three other vacuum lines that originate under the metering unit on a thermistor on the y-pipe. If one is split, it could cause a leak and fail to provide vacuum for the WUR, spark advance, etc.

[David T]

Yes, quite possibly. You can use a good flashlight too - take off the air filter box, shine the light down around the idle speed motor and push in the metering plate and look for light on the left where the POA enters. If you see light, you have a leak. There are three other vacuum lines that originate under the metering unit on a thermistor on the y-pipe. If one is split, it could cause a leak and fail to provide vacuum for the WUR, spark advance, etc.

The leak he saw was most likely the "O" ring for the tube that goes to the idle motor. It fits into the bottom of the mixture unit.

[DMCMW Dave]

There is an O-ring where the fuel distributor is attached to the air metering assembly. It's often missing. I've never seen that cause a significant problem, but it should be there. It's more likely the brass tube. BTW this isn't a vacuum leak, its an unmetered air leak. Subtle but different, and will cause different symptoms.