2002 Sunfire 2.4 bucks under load and on highway when trying to accelerate. Why?


Asked by Apr 20, 2013 at 11:17 AM about the 2002 Pontiac Sunfire GT

Question type: Maintenance & Repair

I have changed the ignition coils, fuel filter, plugs and idle air controller, but the car will
still buck when I accelerate in 5th gear at 65 or just accelerating in 2nd thru 5th at low
RPMs.  What could it be?  If I try to accelerate at high RPMs (2500+), it will accelerate
fine.  It only happens at lower RPMs.

13 Answers


Not an expert on these at all but I'll throw out my 2 cents. You very well could have a sensor issue of some sort. But the first thing that came to mind was the tourqe converter clutch may be locking and unlocking. Assuming its an automatic? That would cause the precieved "bucking" and the fact it does it at low rpm's, thats when the clutch would lock if it were trying to.


Thank you for your quick response. I should have added this bit of information. It is a manual 5 speed trans.


well then. maybe a vacuum leak or egr issue? hard to say. wish I could help more. maybe someone else will chime in wit some better ideas!

Only at low rpm's. I was thinking maybe you are lugging it, shifting too soon, but then it does it at 65?..so I guess probably not.

2 out of 2 people think this is helpful.

motor mount. transmission mount, the delivery of axial forces is getting interrupted, ~shakin' it down (as it were)~

1 out of 1 people think this is helpful.

Thank you all. I will investigate the mounts to make sure they are not worn. This is helping me shake out possible issues and forcing me to think of other important information to help shake out this problem. I can shift normally ( with the shift light ) with no issues at all. If I shift as if I wanted to move moderately fast, RPMs up to 3500 - 4000 before I shift from 1st to 2nd, then the same 2nd to 3rd, etc. I have no problems either. I run into the issue when I am cruising at < 2000 to 2500 RPMs and then hit the gas very hard at all to speed up, to pass for example without down shifting which I should not have to do while cruising at these RPMs. If I down shift, I am ok. However, I still run into this issue when I am at 65 and want to pass that slow moving vehicle. Thank you again for your help so far.

as a front wheel drive vehicle, you'll be experiencing "torque steer", probably isn't noticeable at slower speeds but take it up higher and will swim left on accelleation, and swim right on decel, not much but enough to make you keep your hands on the steering wheel, but axial play will start making sounds if the transmission mounts are degraded. 2002 may stll have okay rubber supports, but would raise an eyebrow when looking at them, not that this is relative to your performance issue, but will "tighten up the show" as it were~ I'd check the timing advance to the rpm's in question~

1 out of 1 people think this is helpful.

I don't think it would cause bucking but the 2.4L has a small hose from the engine to the intake. It's down and behind the intake. Look for it. See if it's clogged or leaking.

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Yeah i was gonna say mounts wouldnt cause this issue but i didnt want judge to get mad at me :(


You can take your car to the parts store to get the codes read. Sometimes there are pending codes that have not caused the CEL to come on. If you have a code, write the number down and post it here.

1 out of 1 people think this is helpful.

kbro, sir- I don't get mad at things that can make sense, yes perhaps the mounts are just fine but when she's rockin' and rollin', buckin' and fussin' loose things can get looser, not tighter....considering the age of the rubber, and complaint thought it might be advisable to have a looksee down there....with a prybar to check for separation...just a thought...must learn to control my thoughts....sometimes they are good ones though~


No codes. I'm going to look into the MAP sensor. There is no EGR system on this engine, or I would be looking at the EGR valve.


I just replaced the coil housing this morning and that fixed the problem. I replaced the coils, fuel filter, MAP sensor, TPS, ICM, plugs, plug boots, cleaned the fuel injectors and tested them, cleaned the throttle body, and finally replaced the COIL HOUSING. This is what finally fixed my problem. The housing looked brand new, no burn spots, no carbon buildup, after a very mild cleaning, there was no grease nor dirt on the thing, but it was apparently bad.

1 out of 1 people think this is helpful.

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