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i have a 92 mx-3 4 cyl 16v sohc when i put my headlights on and the car is in gear (drive or reverse) my idle drops too about 650rpm's when the fan kicks on it bounces between 200-650? why?

I have the same problem with my car it is a 94 4 cylinder. It usually occurs when I am stopped at a red light or stop sign. I noticed that when I turned off my heater that the bouncing seemed to sloww down a bit. "gorman"

i would suggest forst resetting the ecu by removing the battery cable(positive for 15 mins)..if that doesn't work open the idle screw a bit....my car was worse than yours it would almost turn of in reverse when the lights were on and increasing the idle fixed it ..it never fluctuated once in the last year and a half..oh and our cars idle is designed this way to fluctuate when u come to a stop sign so mazda tells me and all 4 cylinders i have seen r like this so don't worry too much

Hey my 92 SOHC 4 cylinder does similar things. At times it goes crazy, and bounces back and forth between almost 0 to about 1000, and eventually levels out at about 500-600. I have done a complete tune up (synthetic oil, double guard oil filter, brand new spark plugs and wires, and a new cone intake filter). After doing all of this, the idle is basically back to normal. I think this is just an mx-3 problem, and is for the most part harmless, although it is very annoying.

do a test on your alternators.....<P>Mine has been doing that for a while now...and I know it's my alternator going on me....Too much electrical load.

thanx i did the battery terminal and now it idles fine lights on or off!

good job man..i wish i had known this when my car was doing it before i played with the idle screw and messed things up... [img]shrug.gif"%20border="0[/img]

i wouldn't dismiss it so easily, mine did that, although with the lights on and off, i gave it a tune-up and it started working fine, but a couple months later (now) i am paying 800-1000 for my new transmission