Faulty servo unit cruise control?
 

My first post so a short introduction: I have a '83 SC Cabriolet. Imported it from the States to the Netherlands 3 years ago. Since then I have brought back the 911 to its former glory. Now I'm just fine tuning little things.

One of those things is the cruise control. My control unit is fixed last year. It works (better) now, but it does not hold the speed. It drops 3-5 km's and then the cruise control restores the speed. This goes on and on. Very unpleasant to drive with.

Today, I performed the checks in the Bentley manual. The second check: "depress clutch pedal with ohmmeter connected to terminal 3 and ground" gives an infinite ohm reading. Probable cause: clutch pedal switch or servo unit faulty. The rest of the checks all went well.

I took out the clutch pedal switch and tested it with the multimeter: it works. My question: if it is the servo unit, what is wrong? Should I replace the whole unit? Your help is very much appreciated!

On my 3.2, I have a vacuum hose on top of the servo. There is a larger breather then right behind it a smaller diameter vacuum hose. Make sure it is tight and not cracked/worn & follow it down to the "T" fitting to insure it also tight at the clamps.

This controls set and speed and check the cable to the throttle body, it should only have 1-1.5MM play.

Thanks. All looks fine, although I was amazed that there is no clamp on the end of the vacuum hose. Same at your 3.2?

"It works (better) now, but it does not hold the speed. It drops 3-5 km's and then the cruise control restores the speed."

Common problem for the old vacuum actuated servo system, i.e. Most likely the cruise control
ECU is bad. That system was analog and the later 3.2 ('87) used a digital system with a motor
actuator.

Yes sir!

Check the cable too, the one attached to the throttle body, mine was too tight, once to spec all is well now.