Hello everyone, this is my first post. Glad to be here and I hope this forum is more helpful compared to the other forum i was posted on for help, never got any decent replies. Anyway, here is my issue. I purchased my car in April of this year, never had an issue except for the fact that when I had the A/C running the car once idled so low it stalled. This caused me to never really use the A/C during the summer. Aside from that, over the past few months the idling issue became a problem with just daily driving with NO accessories on. The problem is about 30-50% of the time I depress the clutch to slow down, the rpms will slowly drop down to 500 or lower, sometimes when i come to a complete stop it will hesitate and shoot back up to 800 rpms and about 10% of the time it drops so low the car stalls out, and then when I try to restart it from that point it hesitates very badly to fire up. This problem happened maybe once a month, then once a week and new it happens just about everyday and i'm sick of it, and my mpg is pretty bad, i'm getting under 200 miles on a full tank, i'd say about 160. I also am pretty sure the car doesn't have the low end power it used to have. When I bought the car the only mods it had were a new intake manifold, lowering springs, MRT H pipe and a short shifter. Since I've had the car I added a K&N intake, SLP LM1 catback exhaust and a trickflow throttle body and upper intake. Like i said earlier this idling issues persisted before I did any work to this car, although over a period of 6 months the issue got worse. By the way, the car is a 2000 GT with 120k. Anyway to combat this issue I have tried multiple solutions. I cleaned the IAC and even replaced it, but the replacement made the car run really bad so i put the stock one back on and just cleaned it up real good, I replaced the TPS and EGR valve, cleaned the MAF sensor with CRC MAF cleaner, i checked the PVC and that's good and i'm pretty sure there are no vacuum leaks. I took it to a mechanic and he replaced the ECT and Oil Temp sensors, and cleaned my air filter and claimed he adjusted some things to richen up the engine because i was running very lean, which really didn't fix the issue, he said i should get bigger injectors and a tune but I don't think that would be causing my issue with the car stumbling while slowing down. I have disconnected my battery multiple times to reset the idle and the car will run better for a few days but then starts to act very bad again. I have also experienced times were the car will backfire shifting gears. Also, this problem usually likes to start when the engine is warmed up to normal operating temperature. I'm running out of ideas, i was going to try the fuel filter next but I really don't think that would be the solution, and i'm really tried of spending money on parts that aren't fixing this issue. Also, to add one more thing, I don't know if this would really matter to my issue but when i'm driving, you can hear a chirping nosing coming from the engine, mostly at idle but sometimes when i'm on the gas could just be a squeaky belt or something not relevant to this issue. If anyone has any idea what to try or do next I would really appreciate it. Thanks for reading my post.