D jetronic problems Options

[Edchina]

Hi,
I have been troubleshooting the D jetronic on my 914-4 1975, 2 liter engine.
Bought a fine car, but the previous owners messed the D jetronic system up.
Vacuum hoses were missing, throttle switch was new but not adjusted, fuel lines clogged up and temperature sensors not connected.
Here is what I have done so far:

-Overhauled fuel tank.
-Installed new fuel pump and filter.
-Checked fuel pressure at the regulator (2 bar)
-Changed all vacuum hoses (no leaks)
-Adjusted valves
-Checked trigger contacts (looked like new)
-Checked dwell angle (46 deg.) and breaker points
-Adjusted timing
-Adjusted throttle switch
-Compression test showed 121 Psi on all cylinders
-Installed new pressure sensor after the old one failed during vacuum test (membrane cracked)
-checked electric system with Bosch tester
-checked electric system manually

Problem:

Engine is running rich and the idle is high (around 1200 RPM).
By installing a vacuum gage between pressure Manifold and pressure sensor the vacuum changes (-0.65 ~ -0.5 Bar) rather than being constant. Adjusting the bypass screw at the trottle does not change the idle much. The CO value is around 4% and does not change much when adjusting the potentiometer at the control unit.

My question is what is causing the vacuum to rise and fall causing the RPM's to increase and decrease by 400 RPM.

Thanks

[JawjaPorsche]

If the intake hoses are 40 years old, they probably need changing. Don't forget the Intake Manifold Gaskets too. Pelican Parts sells both. At least you will eliminate this potential vacuum leak source. Sounds like you are on the hunt. Keep it up, you will eventually find the leak.

While you have the air intakes off, sand and spray paint them. It will really dress up your engine. See picture.