99 chevy lumina idling very irregular
Hello all, hope all is well- i have a 1999 Chevy Lumina 3800 model, with 254k miles on it. Ive recently been having problems with the idle- basically, whenever i would come to a stop, with the car in drive, the RPM's would slip from 800-1000 sharply down to 400, then back up to 900-1000. My lights would dim, and the engine would sound as if its about to stall out. that occured for about a week. also, when i would come to a stop, then go to accelerate, the engine would buck and the RPM's would ruise and fall quickly. When i would shift into park, the rev would go to 1500, then fall all the way down and stall the car out.
I took my car to my mechanic, and he replaced my fuel filter and fuel pump, saying i had no pressure. ($600 total to repair) i get the car back the other day, and its still doing the EXACT same thing.
I am just wondering if anyone has any advice (besides junk it lol) or has similar experiences as to what could be causing this.
Thanks in advance for any and all help!