Has anybody ever tried the chips they sell on Ebay? Here is an example Ebay
The chis is supposed to change the air/fuel ratio to increase horsepower. It's really cheap so I'm skeptical. Just wanted to know if anybody tried this. Thanks
Yes it can work, not the easy way they claim and instruct, but it is possible.
Here is a link where BMW does a resistor installation to make the mixture richer.
Of course it is on a OBD, pre 1996, and not a OBD III, post 1995, car.
OBD II will find the reading faulty and use a different means to set the AFM.
Now for the information:
install an external resistor in the wire for the temperature sensor that feeds the Motronics (should be the one with the light grey connector) Resistor type is 270 ohm, 1/2 watt, "Gold Band" metal film resistor for Motronics Control Units with a Bosch code date of 342 or higher (production date after 9/83) and for Motronics 341 and lower (9/81-9/83 production dates), it is a 560 ohm, 1/2 watt "Gold Band" metal film resistor .
This upgrade was performed at no charge, but may not have been done on your vehicle. If you have the slip on rotor instead of the bolt on type, the full upgrade was not done, but you may still have the external resistor installed under TSB 11 11 84 (920), which was only added to address a complaint of "hesitation/poor throttle response" during several minutes of operation after starting a cold or warm engine at an ambient temp above 75 degrees F.
Second, if your car is not running right and you have questions, make sure to specifiy whether your car has had the upgrades.
Third, the external resistor may be the source of a "no run" condition, if the solder connection breaks from handling the temperature sensor connector. This resistor is usually soldered just behind the connector and may be concealed under the rubber boot. A broken or bad solder connection will mean that your car will not start or run, and this could be an intermittent problem because of engine vibration. In an emergency, you can disconnect a wire to the short 2 prong temperature sensor that feeds the idle control module, and the car will run, but the idle will surge hard. It may be better to carry a short wire with small insulated alligator clips on both ends in your tool kit to do a roadside repair.