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In Reply to: What key words, I've tried several searches... posted by Pat H. on February 25, 2001 at 11:09:46:
Theory:
The amount of fuel fed to the engine is determined by the 1)FUEL PRES and 2)PULSE WIDTH (length time wise) to the injector.
The pulse width is affected by several factors (inc. but not limited to PROM, Temp Sensor, O2 Sensor, AFM Flap Position*...)
*Up to about 3500 rpm only
We are going to modify the Flap Pos'n Sensor by making LESS air open the flap WIDER (Wider=More Fuel). Usually these engines are set at the edge of leanness when new, and as they age, they go leaner, making for poor performance and idle. By "calibrating" we are simply maximizing the engine output for the other parameters using the AFM to "tune" the system.
Doing the Job:
1)Unhook the air cleaner elbow from the AFM.
2) Rotate the AFM 180 deg (M30) so the black plastic rounded-corner plastic cap is on the top (watch the wires).While the AFM is upside down, center the idle CO screw (count turns) in its range.
3) CAREFULLY cut the sealant (RTV) and pry the cap off.
4) Notice the screw holding pressure on the toothed wheel (looks like a gear).
5) Paint a mark on the wheel and the post as a reference mark for future re-setting if desired.
6) Disconnect O2 Sensor at firewall, start car and warm to operating temp.
7) Set RPM to above idle (1500-1800 rpm is fine)and hold it there mechanically.
8) Loosen clamp screw and rotate to maximize rpm.
9) Tighten screw.
10)Check idle smoothness. If it is rough, note present toothed wheel position and try moving 1 to 2 teeth either direction until idle smoothes out.
11)Adjust idle CO screw for edge-of-lean smooth idle. (remember screw works backwards from carb idle adj.) (i.e. CW=Richer)
As an alternative, you can simply adjust the toothed wheel for the smoothest idle (at idle rpm of course) in step "8" above and have done with it. You probably won't notice a big difference at running speeds anyway.
Hope this is fairly clear. If not, ask and I'll modify or try again.
Bob
P.S. You'll notice I didn't mention the O2 sensor again. You can reconnect it, but remember it may TRY to drive the system leaner than you just set. Most "enthusiasts" run open loop w/o the sensor (see disclaimer below).
Another way of doing it to retain closed loop system would be to
1)Replace O2 sensor with a new one (just to be sure)and run it 100 miles (burn it in)before step "2" below
2)Perform steps above (1-11) (except do not disconnect O2 sensor). This will maximize calibration using the Closed Loop mode for emissions. If the engine runs poorly after this method, check ALL the other sensors in the system. If they check good, and you have no air leaks, you may have a computer that is out of calibration. Buy a new $$$ computer (Or run the open loop method above).
Disclaimer: Understand that you MAY be in violation of Federal Law by operating open loop on the street.
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