Erratic Idle "Driving me CRAZY"

mountainbikextremist · 10-25-2008, 11:31 PM

My swiftie is having idle troubles. With many hours spent online and trying this and that I cant figure out what the problem is

, so any ideas would be GREATLY appreciated. First here are my car's specs:
1999 Suzuki Swift
1.3 Liter
4 Cylinder
3 Speed Automatic

This is what she is doing:
It will idle beautifully in in park or neutral but once it is in drive or reverse, the idle speed will erratically drop 50 rpms or so "enough to significantly dim the headlights" and then immediately go back to normal idle. Often times it will do this numerious times in a row and then hold a normal idle for a few mins. Other times it might do it once, and go back to normal idle. It doesnt seem to do it when the car is completely cold, but the engine doenst have to be close to operating temp for this to happen. It will do the same thing in idle in neutral but with the A/C on. "It is related to engine load in idle." I am experiencing no other symptoms besides the errtic idle. Here is the trouble shooting i have done thus far, with no avail:
-Vacuum specs:
*In Park/Neutral: 17.2 in HG
*In Drive: 15.2 in Hg is where it holds steady at "when it does" and will errtically drop to 13 in HG and the immediately back to 15.2.
-Fuel Pressure
*ign on: 39 PSI
*dle- 36 PSI
-Overhauled Throttle Body and cleaned the MAP and IAT sensors
-Checked for vacuum leaks, using propane teachnique, and replaced any worn looking lines.
-No loss of power, and not running rich- so I dont suspect an O2 sensor.
-Un-plugged EVAP purge valve and erratic idle contnues. There is no vacuum bypassing it unplugged. "Eliminating any vacuum leaks between it and the fuel tank."
-The vacuum drops ever so slightly when I push on the brakes.
-One thing that might be important: I have a rather large sterio "two 10 inch subs, powered at 150 watts" in my Swift with no copacitor. However, the erratic idle occures whether the music is on or not. My battery is staying charged, so i dont suspect that the alternator is going out, but I could be wrong.

Thanks!