Bucking when OFF THROTTLE in 4th gear

[Terrorist 5.0]

Just want to come back and mention that the issue was solved. Sometime between when I started doing my clutch and when I finished, the tiny plastic vacuum line that controls the vents broke, and the car went through its relearn process when I reconnected the battery with the tiniest of vacuum leaks. That little leak was enough to send the computer nuts. After fixing it I noticed the issue was getting a little better day by day, so I decided to clear any KAM and disconnected the battery. I relearned the car the next day and the issue is gone. Thanks everyone. Go over stuff twice, I thought I was still vacuum leak free.

 

[GTamas]

What is the KAM? I'm having bucking in first gear when off throttle rolling and getting close to idle speeds.

 

[Terrorist 5.0]

What is the KAM? I'm having bucking in first gear when off throttle rolling and getting close to idle speeds.

KAM stands for Keep Alive Memory. The ECU has some degree of adaptation to the environment that the car is in and the way it is driven, so it can provide more suitable fuel trims and ignition settings. With the vacuum line broken during my clutch replacement from the engine rocking back and forth with the transmission mount disconnected, and the battery reconnected after I was finished, the car learned its fuel trims and ignition settings with the vacuum leak present, which explains why when I fixed it, the car was still “confused” causing the bucking.

 

[Terrorist 5.0]

What is the KAM? I'm having bucking in first gear when off throttle rolling and getting close to idle speeds.

In your case though, I would say this has more to do with drivetrain slop. If your idle is solid, then most likely this is the slop travelling back and forth throughout the drivetrain at low speeds as it goes from loaded to unloaded as the car tries to maintain idle. My car does this too, and every car does to some extent. Mine feels like it wants to leap off the ground when it does it lol

 

[GTamas]

In your case though, I would say this has more to do with drivetrain slop. If your idle is solid, then most likely this is the slop travelling back and forth throughout the drivetrain at low speeds as it goes from loaded to unloaded as the car tries to maintain idle. My car does this too, and every car does to some extent. Mine feels like it wants to leap off the ground when it does it lol

This bucking is quite strong, to the point of uncomfortable. I don't know if it is normal to these cars, I never drove another SN95. Since I have my car as far as I can remember it always didi this bucking in 1st. I did not experience this with any other modern manual/auto car and my previous 79 auto TransAm didn't do it.
Shall I shoot a video, can you say if it is normal behaviour?
Or what is worth checking? I think I eliminated all vacuum leaks last year and I also changed the EGR, spark plugs and wires and O2-sensors last year.

 

[Terrorist 5.0]

This bucking is quite strong, to the point of uncomfortable. I don't know if it is normal to these cars, I never drove another SN95. Since I have my car as far as I can remember it always didi this bucking in 1st. I did not experience this with any other modern manual/auto car and my previous 79 auto TransAm didn't do it.
Shall I shoot a video, can you say if it is normal behaviour?
Or what is worth checking? I think I eliminated all vacuum leaks last year and I also changed the EGR, spark plugs and wires and O2-sensors last year.

Put a video up, couldn’t hurt to get some opinions.

 

[RAU03MACH]

Check mass air flow and cold air sensor

 

[GTamas]

I tried to catch it on video today, but it wasn't doing it, only very slightly which I would consider normal and acceptable. Strange, either Murphy's Law, or the ECU is learning it and I need to force it a few times to learn that condition.
Anyways, I'll let you know some time later if it is gone for good or it comes back.
While I was at it filming, I shot a pull from idle rolling in first, enjoy, have a good start to the week!

 

[Terrorist 5.0]

Im glad i have 3.08’s because 2.73’s look miserable haha, clean car

 

[GTamas]

Im glad i have 3.08’s because 2.73’s look miserable haha, clean car

Yes, it's stock gears and engine. For cruising I'm happy with the performance for now. Don't have big modification plans. Gears I would only change if I have to do something in the diff anyways. Or if it gets boring in the future

 

[Terrorist 5.0]

Yes, it's stock gears and engine. For cruising I'm happy with the performance for now. Don't have big modification plans. Gears I would only change if I have to do something in the diff anyways. Or if it gets boring in the future

I like 2.73's, just not the crawling at low speeds and accelerating hard. If these cars came with a 351, 2.73's wouldn't be an issue. They are great for around town IMO.

 

[badass98svt]

I had a similar bucking issue on an old 97 I had. It would buck when off the gas in 4th and 5th gear. Turned out I left the MAFS unplugged. D'oh.
Doesn't sound like your solution though.