Hunting at idle, only when cold, new performance chip in 3.2

[Greg White]

Recently pluged in new performance chip from Steve W. Performance is excellent (service and help from Steve also excellent) but the car hunts for idle at start-up. Drive a block or so and it is gone and everything is perfect. Is this a computer problem or an Idle speed issue? I switched chips just when it got cold here in Louisville. Thanks, Greg

[Steve W]

Greg, glad you like the performance. Hope the glitching problems you had with your original chip are now gone. If your car hunts idle when cold for the first minute, your idle fuel mixture probably needs fine tuning, because your O2 sensor is still cold and has not kicked in yet to adjust. You can adjust this by fine tuning the idle mixture screw on the air flow meter. Turn clockwise to richen, counterclockwise to lean. A half turn clockwise will probably do the trick. The mixture screw is located on the underside of the meter, and stock is usually covered with an aluminum plug. The diagram below shows it highlighted in red. By drilling two small holes in the plug and using a pair of needle nose pliers, you can pull it out. The mixture screw uses a fine 2.5 or 3 mm? allen wrench to rotate it. Since your car is a Euro 3.2 imported into the U.S. and previously altered to meet U.S. emissions, you may not have the plug there.



Best way to adjust the screw is to disconnect the black O2 sensor wire from the plug from the car, and connect a DVM to measure the output voltage of the sensor with the car at idle at normal operating temperature. Properly adjusted, the voltage should fluctuate evenly between 0.2 and 0.8 volts. Constant voltage below 0.2 is too lean, and constant voltage above 0.8 is too rich.

[Greg White]

Hi Steve, before I bothered you with this, I wanted to see if anyone else had this winter problem. This only occurs when the engine is below, say 40 degrees. Also remember I have no o2 sensor, the car is back to original Euro Spec. Do you still think it is the idle fuel mixture? Thanks, Greg

[Lucky]

Yup, my car does this when cold but only when ambient is below about 40 degrees. When temps are in the 20's it gets even worse and sometimes does this after the engine has warmed.

I've been living with the problem, but now armed with Steve W's plan of action I'm gonna try and eliminate this annoying characteristic. Oh, btw, I have a custom performance chip in my car as well.

[Steve W]

Greg, with or without the O2 sensor, a little fine adjustment of the idle air/fuel mixture screw should do the trick. Sub 40 temps with a cold engine makes fine atomization of fuel difficult, with a tendency for fuel to condense along port walls.

[Greg White]

Thanks Steve it's on my weekend list of things to do or at least try. greg