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2003 Buick Century car stutters at low RPM when warm

Tiny
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  • MEMBER
  • 2003 BUICK CENTURY
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 102,000 MILES
When the engine is cold it runs & accelerates fine. Once the engine is warm it stutters / hesitates at low rpm. The head gasket was recently done & I had to replace the emitions (sp?) Valve because they left it on the manifold. Prior to replacing it I noticed the stuttering. I since have replaced the ignition module & the spark plug wires with little to no improvement. I was about to replace the distributor coils (there are 3) but since it runs fine in the morning before the engine warms up im thinking it's something else.
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Monday, October 13th, 2008 AT 7:09 PM

18 Replies

Tiny
JAMES W.
  • MECHANIC
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Do you have a "check engine" light? If yes, you need to pull the fault code(s) out of memory. This will help diagnoss the problem.
Does it run ok above an idle going down the road?
My first thought is a gross vacuum leak somewhere. You may want to check the lines for disconnects or leaks.
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Monday, October 13th, 2008 AT 7:37 PM
Tiny
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No check engine light is on. It was one prior to replacing the emissions valve and the code was for fuel vapor leak but Ive driven over 100 miles since resetting it and it hasnt come back on.
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Tuesday, October 14th, 2008 AT 4:18 AM
Tiny
JAMES W.
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It doesn't sound to me like ignition (coil). If it were, it should stumble under load. I'm still leaning towards vacuum leak. We can try an old "indian trick" here. Take a can of O2 sensor approved carb cleaner and spray around the intake area while the engine is at a warm idle. If you hit the area of a vacuum leak the rpms will increase and the motor will smoothen out.
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Tuesday, October 14th, 2008 AT 9:02 AM
Tiny
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I'll try that tonight when I get home.
FYI
When sitting in the driveway it idles & rev's up smooth. Will the rpm still increase if I hit a vacumm leak?
When driving the hesitation/loss of power is around 25 mph to about 35mph unliess I step hard on the gas & kick it into overdrive. If I'm going up hill it's really noticable until about 40-45mph
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Tuesday, October 14th, 2008 AT 12:15 PM
Tiny
JAMES W.
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I stand corrected. If your idle and rev-up is smooth, it's not a vacuum leak. Let me do a little research and I'll get back to you, Jim
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Tuesday, October 14th, 2008 AT 1:17 PM
Tiny
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Also I noticed tonight that even when I get on it and the hesitation stops it still seems to lack power.
Thanks for any help you can offer.
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Tuesday, October 14th, 2008 AT 10:53 PM
Tiny
JAMES W.
  • MECHANIC
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This bugger is keeping me awake at night.
There are 4 things in the fuel system that could cause this problem. #'S 2-3 & 4 are supposed to be monitored by the computer and "should" trip a check engine light if they fault. I'll list them by "order of suspicion".
1- fuel pressure regulator (checking this comes later)
2- mass airflow sensor (MAF)
3- throttle position sensor (TPS)
4- crankshaft position sensor (CPS)
Suspects in the electrical system
1- an ignition coil
2- crankshaft position sensor (controls both injector pulse and spark)
3- Computer itself (ECM or PCM) same thing.
Let's unplug the vacuum line to the fuel pressure regulator and plug it. Also, looking for raw fuel in the vac line or at the regulator port. Take the car for a little spin, I wish I could ride along, and see how it runs. I'm not a parts replacer like, "change this part, oh well, that didn't work, let's change this." It cost too much and I like to be reasonably sure that what I recommend is going to solve the problem. Worse coming to worse, you may have to take it in and have it "hooked up" to a diag. Unit that can test the range position of all the sensors and the ign.
I printed a set of computer engine diagrams for your car. If you have acess to a fax machine, I can send them to you. They are more detailed than you get in most books. Let me know on the regulator test, Jim.
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Wednesday, October 15th, 2008 AT 1:45 AM
Tiny
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My fax # is 714-459-7373 if you want to fax it. I'll have to go to the auto store and get me a book since I'm not sure where most of that stuff is on this car & let you know on the regulator test once I try it.
Thanks
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Wednesday, October 15th, 2008 AT 9:19 AM
Tiny
JAMES W.
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Fax was sent today.
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Thursday, October 16th, 2008 AT 4:04 AM
Tiny
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I plugged both the vacumm line & the regulator & t seemed to run smoother. Does that mean the regulator needs to be replaced?
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Thursday, October 16th, 2008 AT 1:31 PM
Tiny
JAMES W.
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If going down the road, normal driving, and you have lost the hesitation, I would say yes.
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Thursday, October 16th, 2008 AT 4:14 PM
Tiny
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Thanks, I'll hopefully replace it this weekend & let you know. The hesitation is definitly gone. It still seems to lack a little power but I'm assuming because it's disconnected right now.
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Thursday, October 16th, 2008 AT 4:23 PM
Tiny
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***sigh*** I replaced the fuel pressure regulator & it seems a little bit better but it's still there.

Wierd thing is before I replaced it, on Saturday night the check engine light came on for a little bit then on Sunday morning it was off. The check engine light does work & come on before I start the car so I know the bulb works.
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Tuesday, October 21st, 2008 AT 8:44 PM
Tiny
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Well tonight it felt even worse then before. I'm at a loss, once I hit 25 or 30 mph the bottom falls out & I feel like a dying horse is trying to pull it. What test can I possibly do to check the other stuff? Still no check engine light comes on. If it is a coil would a light come on?
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Friday, October 24th, 2008 AT 12:29 AM
Tiny
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Finally the light came on. I think the code was p3000 & the message was multiple random misfires. Is there a way to check the crankshaft position sensor? Or is it the coil?
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Sunday, October 26th, 2008 AT 8:37 PM
Tiny
JAMES W.
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The only way you can check a CPS unit is to have it hooked up to a diagnostic unit. They can check the coils at the same time.
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Tuesday, October 28th, 2008 AT 1:56 AM
Tiny
DYOUNG81
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I'm having the same problem. Did you figure out what was causing it!
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Friday, January 16th, 2009 AT 2:53 PM
Tiny
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It ends up that the catalytic convertor is clogged. I havent been able to afford to fix it yet so I can't say for sure but it makes sense. I finally ended up taking it to a friends shop who spent about 2 full days looking at it & running diagnostics
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Friday, January 16th, 2009 AT 3:32 PM

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