Pulsating Idle

Hi. I have these pulsating idle problem. my RPM goes up, down,up,down. I first noticed this on while on stop with the AC on. I tried turning off the AC and it still pulsating.And when I drove without AC the idle seems ok, and then I stopped again, it starts to pulsate again. I cleaned the throttle body thoroughly coz i thought this is whats causing it. I started it, at first the idle is ok then when i run the car and when i stop the pulsating starts again. I remember the day before it acts like this, while inspecting under the hood, I noticed a disconnected plug or a prong(or whatever you might call it) and I connected it thinking it was accidentally disconnected and it fits anyway no doubt about it. this plug is located on the firewall (wiper side).what is this plug? eversince I connected this, the idle becomes pulsating. when I unplugged it, the idle rises up without pulsation! when plugged, the idle goes down with pulsations! i have to adjust it up just to make it stable! please anyone help please. I dont know what to check next. thanks

I forgot, My ride is a 1994 galant

spark plugs ??? how old r they mine 99' G did the pulsating idle and it was the plugs

thanks for the reply. I was thinking of the sparkplugs too. my sparkplugs are almost 4 months old. But what confuses me is that the idle runs ok when this 3 prong triangular (switch?plug?connector?) thing attached to the firewall on the wiperside is disconnected. I dont know if this is connected to a sensor.if this is disconnected its normal idle. but when i connect it, idle screw up. I want everything in the car to be standard thats why i want this thing connected. Im also afraid it might cause or create any other trouble unknown to me if this is disconnected. I will change the sparkplugs for now and I will post whatever the outcome is.

can you tell me the year and model of your car and i can look it up for you and try and figure out what this plug is.

take a pic of the thing.

i have the same prob as with your 7g.There were even times when the idle just goes wild over 3K RPM.I think its the serbo. Here in the philippines, theyre selling a surplus for 3.5k pesos, its kinda cheap.But no guarantee on how long it will last.

check the servo. the servo has everything to do with idle. mine got broken several times -the servo's magnet and gears. not sure though what plug u r referring to.

Mine does the same thing sometimes. Only at a stop and it'll drop rpm's every once in a while. Died once or twice because of it. Mine doesn't spike up though only drops and then goes back to normal.

https://www.thegalantcenter.org/showthread.php?t=42787

looks like IAC motor is going bad.

sounds like the god awful IAC/FIAV is going bad, which is it's job, to go bad

I have this problem which is perfect now I can slip a 60mm TB under the ever inquiring eyes of ...dunh dunh ..the wife this is lovely
She is always suspecting me of tryna make my cars faster

Well I never ;-)