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Car bucks around 2000 RPM. Transmission, spark plugs, or fuel?

2008 Buick LaCrosse intermittently does funny stuff around 2000 RPM. “Bucks,” “lurches,” and “revs” are some fitting words. When I give it gas to get above 2000 - or let off the pedal - it seems to do fine. Sometimes it’ll go a whole trip without any issues at all. Most consistent problem spots are under load (climbing a hill) at 40+ mph right around 2k rpm. It FEELS like its starved for fuel. That lurching feeling you get when you’ve completely run your car out of gas right before you roll to a stop, if any of you know what that feels like.

One guy thought it might be an issue with the Torque Converter Clutch Solenoid. There’s close to 98k miles on the transmission, so it’s not buttery smooth by any means, but it doesn’t seem to slip or “shudder” any notable amount. I also read someone else’s post on here saying a similar issue came down to a misfire and changing the spark plug and line cleared it up.

No check engine, no codes, nothing to go on right now but one guy’s opinion. I’m going to start with what I know; new fuel filter, replace spark plugs and wires, keep an eye on the tranny fluid. I was just wondering if anyone had any other ideas before I go ahead and drop out the transmission.

When mine did that it was the crank sensor. You can try going out of overdrive to 3rd gear and see if you have the same shudder to try and rule out the trans. Really though, a computer diagnosis plus testing the fuel pressure would be in order to try and determine fuel or spark. You have been changing the tranny fluid at 30K or so?

I ran it in 3rd and the shudder was still there. It’s more intense in overdrive, but I still had issues around 1500 to 2000 RPM in 3rd, especially when climbing a hill. Would this rule out the torque converter?

I don’t know the complete maintenance history. The fluid off the dip stick is clean and red.

If it does it in both gears IMHO it’s unlikely to be transmission related. OTOH, if it’s not there should be a code.

I did a stall test and the tach peaked around 2800 RPM, which seems a little out of bounds.

I am not a mechanic but AFAIK normal stall speed for a typical automatic transmission is 2300-2700 RPM. Your result of 2800 RPM is iffy but I still doubt it’s the cause of your bucking. Unfortunately I don’t have any other ideas.

Little late, I know. It’s been on my mind and I wanted to give you guys an update, though.

  • Brand new plugs and wires; no help.
  • '08 Buick LaCrosse has no fuel filter. Pfft.
  • Bonus problem: One of the crimps on the power steering lines started bleeding hydraulic fluid like a stuck pig.

I ended up getting another opinion in person on the transmission. It did end up being a slipping stator. I had a tranny rebuild done and they went ahead and threw in a new power steering fluid line and new sway bar for good measure. No more “bucking,” “lurching,” or “reving.” Plus, now I can steer safely. :smile:

You guys are great! Thanks for the ideas!!