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MVP Tech Tips

Setting base idle specs. on cars with K-Jetronic fuel injection and CIS

Many driveability and running problems can be traced to improper base engine settings. Setting your base idle specifications is always the first step when trouble shooting any runability problem. By following the steps below the source of most problems can be identified

1) Check for air leaks by spraying carburetor cleaner on all intake hoses and gaskets including the injector seals. Any fluctuation in idle while an area is being sprayed means a leak. Repair any leaks you find. Don't spray carburetor cleaner on hot manifolds as it may cause a fire.

2) Remove and clean the throttle body, then reinstall it using new gaskets. Make sure the throttle switch clicks as soon as you crack the throttle (adjust as needed).

3) Start your engine and let it warm up fully.

4) Set ignition timing to the manufacturer's specs.

5) Now use a voltmeter to verify that your 02 sensor is working properly. Connect the red probe from the voltmeter to the 02 sensor wire where it is connected to the large green wire. Connect the black probe from the voltmeter to ground. A good 02 sensor will fluctuate between .2 and .7 volts if your mixture is anywhere close. Replace the 02 sensor if needed.

6) Go to the left inner fender well and find the blue and white pigtail that sits besides the ignition ECU. This is your CIS test point. Ground this connector and adjust the throttle plate to 750 RPMs. Readjust the throttle micro switch as needed. Remove the ground from your test point, the idle should be close to 850 RPMs or 950 RPMs on turbos.

7) Next to the blue and white wire is a red pigtail. This is your CO test point. Using a DVOM that measures duty cycle connect the red probe to the red pigtail and connect the black probe to ground. The proper duty cycle is around 50%. Adjust the base CO through the small hole in the air flow meter using a long 3mm Allen wrench. Adjust it to 50% duty cycle. A dwell meter may also be used to set the CO. With a dwell meter adjust the CO to 45 degrees.

Congratulations! You have just set your engine's base idle specs.

Note: With CI fuel injection the lower the duty cycle or dwell, the richer the idle fuel mixture. Factory specification for base CO is a duty cycle of 54%-65% translated to a dwell reading of 49-59 degrees. In our experience we've found that a slightly richer idle CO provides the best idle and the best starting.

Don't disconnect the O2 sensor for any of this.

If your dwell meter doesn't have a 4 cylinder scale use the 8 cylinder scale and multiply the reading by 2. 22.5 degrees on the 8 cylinder = 45 degrees for your 4 cylinder engine.

If you don't know how to use the volt meter post back.


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'80 DL 2 door, '89 DL Wagon, '15 XC70 T6