should i be worried? because i am...
 

ok guys, having some issues here and im stumped...here it goes
ps, sorry if im posting in thewrong section. thinking its a tb issue thats why im here

the car.... a 1998 z28 M6 car with 90000 miles

Driving during the day.....

While doing so, i noticed that when i pushed in the clutch and held it, the rpms would drop and stay at 1400 rpms instead of the regular 1000. ok no big deal. My check engine light did come on, but it has been on and off for a while no because of my right rear o2 sensor

Go to start it tonight, and this happens......
no check engine light anymore. I start it, and it starts, but kinda struggles to keep running. rpms are around 800ish and this has never ever happened before. start driving right away. as i go to shift from 1st to 2nd, rpms drop a lot quicker than usuall, and go straight down to 750-800. shift to second. drive, shift to third...does the same thing. I hold the clutch in for a little and it just stays all the way down at 750-800. everytime i push in the clutch, the rpms drop very quickly down below idle. i keep driving and even when warmed up it does the same thing. if i hold the clutch in, come to a complete stop, the rpms again drop to 700, then rise a little to the 750-800. also, i was going down a big long hill, and i put it in neutral for the hill. during my descent down, the rpms would go to 900, then 2-3 econds later drop to 750. then immediately goes back to 900. did this for the entire 3 seconds down the hill. i pull into a gas station, after ten minutes since startup and its fine. idling at 1000. rev it up, drops back to 1000. operating normal. let it sit for a few minutes whilepumping, start it up and its fine again. My idle oil pressure is normal at 30, not sure if relevent. any input is greatly appreciated. thanks

What all is done to the car? When was the last service done? Help us help you.

bone stock minus a flowmaster.... last time at the shop wqas 5000 ago for brakes. Started up today and it was fine all day. idk

Check every sparkplug and wire? Almost sounds like what mine did when I accidentally left a plug wire off of a coil (shh... haha)

Replace the o2 sensor, do a basic check-up. Air filter, MAF sensor, plugs, wires, etc. When was last fuel filter change, oil change, battery, etc. Original alternator? Do you experience really bad voltage drop? I had this issue in my A4, and I did the big 3 and 145amp alternator and it went away.

.there is nooooo performance loss at all. zilch. so that rules out ignition and possibly fue filter...won't hurt to check wires...hell maybe ones lose. I remember looking and the whole time my amp gauge was reading 14 so that's good. air filter isn't bad..... a buddy of mine said idler motor may b starting to go