Originally Posted by JReed615
For about the past 6 months my RPMs will dip down to a couple hundred RPMs. It only happens when I'm decelerating (with or without clutch depressed) and sometimes when I'm stopped. I assume it's the IAC or something else in the throttle body but I'm not sure.. Any ideas? Will cleaning the assembly fix it? Or replacing the sensor(s)?
I'd bet a sticky/dirty IAC (Idle Air Control module) as well. When the IAC sticks, it doesn't let enough air into the engine which will cause unusually low RPMs. A vacuum leak would cause higher than normal rpms so I wouldn't expect that to be the cause of your abnormally low rpms.
Spraying a can of aerosol Throttle Body Cleaner through the throttle body while the engine is at idle rpms will normally clean an IAC that is malfunctioning from being dirty. At idle engine rpms, the IAC will suck the cleaning fluid into itself which will usually stall the engine. That's fine, restart the engine and let that happens several times. The IAC won't suck cleaner in through itself at higher than idle rpms so do this at idle rpms.
Once the IAC has received maybe a third of the can's contents, finish the rest of the can on the throttle body's interior at higher than idle rpms.
No guarantee the IAC is causing your low RPMs but cleaning it with throttle body cleaner is cheap and easy to do. If doing this job properly doesn't cure the idle issue, I'd then immediately suspect a bad TPS (Throttle Position Sensor) which is also mounted on the throttle body. Unfortunately, the TPS has to be replaced when it goes bad, it can't be cleaned like the IAC can.