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82 zx, on the AFM adjustment screw (mixture), is there a cap screw covering the adjustment screw. The screw is see, is bottomed out and very hard to remove and I didn't want to break something. Any info would be great. Thanks is advance. Lee
 

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If you are talking about the idle enrichment screw, it should be located on the driver side rear of the AFM. From the factory they were set, and sealed with a cap. Most are now missing.

If yours is bottom out (fully clockwise), then you are probably running rich. CCW will lean it out, CW to richen it. You can try adjusting yourself, by ear and engine feel, but your results are not certain. The best way to set this is with the proper equipment (which most of us don't have at home). You can use an A/F ratio meter (stoichometer) to help you tune it. You want the car to be slightly rich at idle. Lean idle is bad for your engine, causing high engine temperature, and possibly engine failure. A rich condition usually just causes you to pay more for gas.

An alternate method is to tune by mileage. After getting it close to where you think it should be (by monitoring engine rpm, idle smoothness, etc), watch your gas mileage for the next tank or so. If mileage is poor (less than 15-16 mpg city) lean it out slightly (quarter to half turn). Then monitor the next tank. You should see the mileage improve. When you start seeing 17-19 mpg, you are probably close to where it should be set. Note that you might need to reset your idle after adjusting this screw, since you are changing the amount of air that flows during idle. In order for the above method to be used, you must keep the idle speed constant. If it was set at 800 for the first tank, it should be at 800 for all of them.

The best way to get this set is to take it to the shop, and have them set it for you. They have the equipment to set it right the first time, with no guess work.

Ideally, these things are set right at the factory, and don't need further adjustment. Unfortunately, many people like to tinker with every adjustment they can every time they have a problem. This one is a prime candidate. Remember that this adjustment only affects your idle performance, and shouldn't be tweaked to solve other runablity issues.
 
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