WHY DOES THE CAR BUCK AND SHUDDER?

1995 Pontiac Grand Am

Tiny

Grand Am

August, 16, 2012 AT 12:42 AM

The car works fine other than this one problem. It shifts beautifully and runs well until I get to a cruising speed on the highway. After letting up on the accelerator and coasting for awhile, when I try to re-accelerate the car bucks and shudders until I let off or punch it into passing gear, and then it is fine again until I cruise and re-accelerate again. It occurs most often in the 80 to 100 km/hr range. I am not quite sure if it has to do with the transmission and or controls, or the engine gas delivery or controls. I am aware that having codes checked would be a good place to start, but I was hoping to get an educated opinion first. The check engine light does come on but does not always stay on. What do you think, any ideas? Thanks!

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14 Answers

Tiny

racefan966

August, 16, 2012 AT 12:46 AM

Ok so do you have a digital multi meter? I am thinking of testing the TPS.

Tiny

Grand Am

August, 16, 2012 AT 12:59 AM

I do have a multimeter but It might be messed up. I can never seem to get it to read correctly. If I get a good tester, how would I do the check of the tps?

Btw, thanks for the lightning quick response! I wasn't expecting that. : O)

Tiny

racefan966

August, 16, 2012 AT 1:05 AM

Ok so you will back probe the green wire put the positive there and then ground the other lead. Now with the key on engine off slowly open the throttle. You should read with throttle closed about.8 volts and it should increase steadly with no drops or glitches to 4.5 or 5 volts. Let me know what you find and we will go from there.

Tiny

Grand Am

August, 16, 2012 AT 1:12 AM

Ok, thanks! I'll have to do that later when I get a decent multimeter and get back to you. Probably another day.

Tiny

racefan966

August, 16, 2012 AT 1:14 AM

Ok that works let me know what you find.

Tiny

Grand Am

August, 16, 2012 AT 4:44 PM

I get.6 closed up to 4.42 open. If I disconnect the sensor and test the wire I get.8 but it drops when connected to.61

Tiny

Grand Am

August, 18, 2012 AT 2:50 AM

So do these readings indicate a problem or would that be normal? What would be the next step?

Tiny

racefan966

August, 21, 2012 AT 2:42 PM

What engine does it have? The sensor readings are normal on that one. Sorry it took so long to get back to you.

Tiny

Grand Am

August, 21, 2012 AT 9:51 PM

It's a 3.1 litre v6.

Tiny

racefan966

August, 22, 2012 AT 3:00 PM

From what it shows you should have a mass air flow sensor. What I would like to have you do is get a can of mass air flow cleaner and clean it. Let me know if that helps.

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