99 Buick sputters between 45-60 mph

Hello, my grandma left me her 1999 Buick Century. Runs and looks great, but it kicks and sputters between 45-60 mph, then is fine otherwise. I’ve changed the plugs, wires, coil packs, fuel filter, fuel pump, and I’ve cleaned the MAF sensor. All to no avail. It has 143,000 miles on it.

What engine? Is the check engine light on? If it is, what are the codes… in the form P1234, please.

Have you done a compression test on the engine?

Engine is the 3100, no check engine light. No I haven’t done a compression test, because I don’t have the equipment, unfortunately.

Not sure if it applies to you, but a friend had to have a torque converter replaced for similar issues on a Malibu. Your car is shuddering: A faulty torque converter can cause a shudder just before or after it locks up at cruising speed. You might feel the car shudder while driving about 30 to 45 MPH.

You might consider going over the intake tract between the throttle body and the MAF sensor. An air leak of any sort between those 2 points can lead to a problem like this.
Also check the PCV hose for cracks, loose fit, etc.

And sometimes cleaning a MAF just might not work.

Does the check engine light work ? Does it turn on when starting engine and then turn off once started?

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Yeah it seems to work fine, just no codes being sent I suppose.

Has the transmission fluid ever been changed? That’s where I’d start.

Now that you have spent a lot of money on unnecessary parts, it might be time to spend some money on a diagnosis. When you take it to a mechanic, ask how he will diagnose it. If he tells you what tests he will run, leave it with him. If he tells you what parts he will replace next to try and solve the problem, try another shop.

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Funny you say that, I actually scheduled one yesterday… Have to wait 2 weeks but hopefully it will pinpoint the issue… I didn’t mind giving the old girl a tune up and a new fuel filter… The pump is disappointing though. Not to mention I’ve had to do all these repairs while having a broken hand. I do appreciate everyone’s comments, I really hope it’s not the torque converter. I’ll update after the diagnostic.


Unfortunately, a lot of shops throw parts at a vehicle rather than diagnosing it. Maybe not “a lot of shops”, but that is what I ran in to, and the worst offender happened to be a dealer. It’s cheaper for me to throw educated guess parts at a problem than it is for me to pay a shop to throw educated guess parts at a problem, so I generally try to avoid taking a vehicle in to a shop unless it’s a last resort (or a transmission issue, as I’m lost other than replacing fluid and filter). May be that the poster has had similar experiences. I would’ve stopped short of replacing all of the coils without a misfire code and I wouldn’t change the fuel pump without having the fuel pressure checked. The rest of what he replaced, I’d go along with that.

Any chance this could be an issue with the fuel pressure regulator? I’ve never had an issue with one, but is that something he could easily check before it goes to the shop?

OP, you might try driving the car in 3rd gear at that same rpm range you’d normally be in when the car is in overdrive at the speeds you mentioned. If the sputter persists in 3rd, it’s most likely not the torque converter.

Did the car sit for any length of time, How old is the gas ?