When at a stop or going up hills it pulses from first to second gears

2001 CHEVROLET MALIBU
254,000 MILES • 3.1L • 6 CYL • 2WD • AUTOMATIC
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MATTSTER76
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I have replaced the transmission filter and flushed the system twice. I changed the plugs, TPS, ECT, MAF, MAP, cleaned the throttle body, intake pipe and upper intake, cleaned the PCV and got a newer EGR from the scrap yard and replaced the front wheel bearings. Needless to say, a bunch of money and time. So, any help or Ideas would help. I also checked the cat am getting 3 PSI replaced the fuel pump and regulator. I'm getting 55 PSI at idle and when I turn it off it doesn't go down at all. Also, have replaced up and down stream o2 sensors.
May 9, 2022 at 1:57 AM
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JACOBANDNICKOLAS
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Hi,

I need a better understanding. What happens at a stop? Does the idle speed fluctuate? It can't shift from first to second, so I'm trying to get a better understanding.

If that is the case, you may want to check the idle air control valve (IAC). The IAC is responsible for maintaining idle speed. It is located on the throttle body.

I would check there first. I attached a pic of it below. Pic 1

Here is a link that explains how to service one. Try this and let me know if it helps.

Take care,

Joe

See pic below.
Image (Click to enlarge)
Attached Media
May 9, 2022 at 7:21 PM
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MATTSTER76
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No, the idle is good 800 RPMs it's when it's in first and between 2,500 RPMs and 3,000 RPMs it's like it shutters or surges between shifts but when on a hill from a slow start it's worse. It seems to up and down shift properly if you floor it. But I have also noticed in 2nd or 3rd if you're trying to pass someone there's like a big blank spot in the gas pedal where it doesn't do much and then it will shift down to 5,000 RPMs . Hope this helps, thanks.
May 12, 2022 at 2:31 AM
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JACOBANDNICKOLAS
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Hi,

If you have a live data scanner, could you check the short-term fuel trims and let me know what they are?

Let me know if this is something you can do or have done.

Joe
May 12, 2022 at 7:14 PM
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MATTSTER76
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Okay, will do.
May 15, 2022 at 3:09 AM
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MATTSTER76
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hi, i figured it out. i cut the cat out and now i have all kinds of power and it's shifting better. thanks for all your help and time.
May 18, 2022 at 6:47 AM
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JACOBANDNICKOLAS
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Hi,

Thanks for the update. A converter can certainly do that. I'm glad to know you got it fixed.

Take care and please feel free to come back anytime in the future.

Joe
May 18, 2022 at 6:49 PM