weird idle

[98StangGT]

My car is idleing pretty rough, like a knock, but then when I turn my AC off, it idles smooth??

[SpectorV]

sounds like you might need to clean your MAF sensor and perhaps idle bypass valve (IAC) these control the idle and rpm's. If the MAF is dirty all sorts of issues can arise. This seems to surface with K&N equpied cars more as they have oil and the oil gets on the sensors. A bottle of No Residue ON contact electronics parts cleaner from autozone can do the job for the MAF. You may have to replace the IAC. It is on the upper intake almost always and is in the shape of a cylinder.

[98StangGT]

So i jus use that residue cleaner all around the MAF and where it connects to? and I cleaned my IAC the other day, I took it out, and sprayed some throttle body cleaner in it

[SpectorV]

You can remove the sensor from the maf housing (if its the oem air intake setup) else you can use a tamper proof torx bit to unbolt the MAF sensor and carefully lift it out and spray it down. Do not use any carb or brake cleaner use NO residue electronics parts cleaner on the MAF sensor.

[98StangGT]

I have a after market cold air intake, but I will try that no residue