First, we checked for vacuum leaks and cleaned the idle stabilizer valve. Almost any hose under the hood is a good candidate for a leak. Pay particular attention to those on the back side of the engine, where things get hot. As a precaution we usually replace the factory cloth-covered rubber hoses with long-lasting silicon tubing. Ron stocks this good stuff, which seems to last forever. It's a nice shade of blue, too. A foot or too will replace all the little bits and pieces from the throttle body to ventilation system and to the spark computer.

      Cleaning the idle stabilizer valve was as simple as removing the hoses from the valve, and spraying carb cleaner in to remove any excess oil blow-by or gunk. We then replaced the hoses.

      We looked at the hoses that connect the brake booster, the breather hose, and idle stabilizer. It's especially important to check the rubber O-ring seals around the injectors, a common source ofleaks. We also checked out the boot connecting the metering unit and the throttle valve. This is especially a problem on the 8V A2 GTIs and Jettas, although it usually causes drivability problems instead of a bad idle. It can be caused by a bad motor mount, by the way.

      Ron used a professional trick that you can easily duplicate to help diagnose hard to find leaks. He sprayed carb cleaner on the idle stabilizer valve joints, and at each of the hoses, as well as in the injector sockets. Why? The carb cleaner is a fast burning hydrocarbon, and if there was a vacuum leak, we would know immediately by the idle speeding up as the carb cleaner is sucked in and burns. Keep carb cleaner away from the exhaust manifold, by the way, and only work in a well ventilated place.

      If everything checked out okay with the vacuum hoses and the idle is still bad, we're ready to proceed with the next step, checking the basic idle setting. CIS-E cars can have the idle accurately adjusted with a simpie duty cycle or dwell meter.

      You remember dwell meters, right? They used to be needed to adjust ignition points back in the dark ages. While they sell special duty cycle meters, you can buy an inexpensive dwell meter to do the job. You may even find one at a garage sale for a few bucks. The 90" scale on a dweli meter equals the 100% scale on a duty cycle meter. That means that 45" dwell = 50% duty cycle.

      You connect the test leads of the dwell meter to the duty cycle test connector. The connector is iocated in the harness by the ignition coil, two wires in a nylon connector with a plug.

 

      Uncover the connector, and insert the test leads from the dwell meter into the connector. Don't force too large a test lead as it could damage the connector. We've found it handy to insert a couple of finish nails or paper clips to make the connection easier.

      The test procedure requires a few changes. There is a charcoal canister "T" fitting in the air flow sensor boot. Remove the "T" and turn it to insert the side with the 1.5 mm restrictor hole. (See photo) The crankcase breather hoses can be either clamped shut, or disconnected. Start the engine (it's warm, right?) and check the duty cycle.

      The correct duty cycle setting for all cars we're discussing here is 26-30% duty cycle, or 23-27" dwell. Ifit's in the ball park, it's time to go on to the next step after unclamping the breather hose and returning the "T" fitting to its correct position.