I have a 05 Fxt with a stage 3 setup and a pro tune through AP. The car have been like this for a while and has worked well. However lately it has had rough idel and has been a tough one for me to figure out.
At idel is the only time it does this, the rpm are steady within about 50rpm either way. But monitoring the afr I see it is jumping around a fair bit. It will fluctuate from 14 to around 15.5 and anywhere in between and when it jumps around it is causing a roughness felt through out the car. Once the car is rolling it has no issues and works great and even seems to improve a bit when the AC is on and has no idel issue when it is cold warning up on high idel.
I was having some surging issues at part throttle so I replaced my front o2 which did solve that issues but did not fix the idel. At least I can narrow it down to know that sensor is not at fault.
If any one has any suggestions of where to look for causes to this problem it would be a great help. The only ideas I have at the moment are perhaps a leaking bpv as it is stock or maybe a bad maf sensor. Both of which I can switch from my wifes car to rule those out.
One again any one with experience with this some help would be awesome.