2000 Buick Century 3100 engine, it bucks at idle or in park
 

I have a 2000 Buick Century with 3.1 3100 engine has roughly 128k miles the car will sometime buck a little, it only last for a few seconds, then goes away it helps if you feather the gas pedal it does not do it while driving it only after you start it and its in Park or if you pull it down into Drive and it will buck some like the idle is going up and down, I replaced the IAC, TPS and its still present I also cleaned the throttle body, car does not miss, runs great when driving it, I dont know what to look for please help! I also scanned the car for codes and no codes, thanks!

Check for vacuum leaks. There a line going from the intake to the back of the motor called the breather tube. Your might be leaking, or have come out of the back of the motor. Mine came off a few months ago, and caused a real erratic idle every now and then. Also, check your PCV valve. It could be plugged. Its only $5 for a new one, so even if it hasn't been replaced in a long time, its worth it to get a new one.

*When was the last time the Trans fluid and filter been serviced? Buick said it's a 1000,000 mile fluid when it's only a 30K mile fluid.
*PCV could be one of those things. It's $2 part and only requires a level 1 in difficulty.
*Next could be the EGR. There are a few videos on how to clean that out with cab/throttle body cleaner(If you still have some left from the Throttle body cleaning you did.
*Fuel Filter could be it
*You do spark plugs and or wires?
*Worse case Fuel Pressure regulator or Injectors.

thanks for the responce!
I just recently replaced the tranny with a low mile 40k unit all fluids seals and filter were changed, I also put a new egr and cleaned out the passage because it was blocked, its the original plugs and wires, and original fuel filter, original pcv valve I will have to ck it out thanks

Yeah they said the spark plugs were a 10K mile item too. Scratch that as well as the orange Dexcool antifreeze. PCV is the cheapest easies item on that list. I haven't done the plugs yet but I have rotated the engine forward on a 3400 to part it out. Not as scary/heavy as I thought it would be.

this is the line 2k2cse is referring to

https://www.buickforum.com/forum/att...3&d=1320249477

I will have too ck that line out! thanks!!!

Make sure your engine is cold when you change the PCV valve. They can get pretty hot. I learned that the hard way lol

Ok, changed out the Pcv valve and the little rubber elbow on it it had a split in it, unfortunetely it still does it, I checked the plastic tube it is connected in the spot in rear valve cover, I am still trying to figure it out, any help appreciated!

Try changing the fuel filter next. You can try cleaning the MAF sensor too.

And the plugs.