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Old 06-04-2015, 01:17 AM
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mgordon18
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Default Mild "bucking" under mild acceleration

While driving last week, my 2006 S 6MT started mildly bucking under acceleration. It's the kind of bucking that happens when you're first learning to drive stick, you know, and you don't let the clutch out exactly right? It's like that but much milder, but you could definitely feel it. Another way to describe it is it's like coming off and on the throttle a touch.

The car would do this not only coming off the line, but out on the highway as well. I'm in 5th gear, 3200rpm, and give it a little gas to speed up a bit, and the bucking would start. As soon as I let up off the accelerator, it would smooth out. Back on the accelerator and it would start again.

As I drove the 60 minutes to my destination it went away completely, and didn't show up again on the way home. The drive home was 4 hours later, so the engine started off cold.

Any idea what this could have been? Scared the crap out of me when it was happening, but then it disappeared...

Thanks in advance,

Last edited by mgordon18; 06-04-2015 at 04:08 PM.
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Old 06-04-2015, 02:04 AM
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Pho King Fast
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Could be fuel pump, ignition wires, coils, MAF, injectors, or maybe just bad fuel.
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Old 06-04-2015, 02:31 AM
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Alexandrius
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Originally Posted by Pho King Fast View Post
Could be fuel pump, ignition wires, coils, MAF, injectors, or maybe just bad fuel.
Wouldn't those throw codes?
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Old 06-04-2015, 07:47 AM
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TommyV44
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Let the dealer (or your mechanic) look at it. I had the same issue many years ago with a 2006 and it was a huge issue (nor saying yours is at all).

Mine was intermittent as well….just check it out.

Tom
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Old 06-04-2015, 09:01 AM
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mgordon18
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Tommy - what did yours end up being? I want to make sure I know all the possibilities. I'm planning on doing some "spirited driving" at the end of this month, so if it's something, I want to get it rectified ASAP.
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Old 06-04-2015, 09:50 AM
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Originally Posted by mgordon18 View Post
Tommy - what did yours end up being? I want to make sure I know all the possibilities. I'm planning on doing some "spirited driving" at the end of this month, so if it's something, I want to get it rectified ASAP.
Man, you sure do plan ahead.
How do you not do some spirited driving every day?
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Old 06-04-2015, 10:38 AM
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Originally Posted by Hella-Buggin' View Post
Man, you sure do plan ahead.
How do you not do some spirited driving every day?
Note the quotes. I do some spirited driving all the time. But a few times a year, I do some "spirited driving."
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Old 06-04-2015, 02:36 PM
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Please let us know what happens I'm curious.
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Old 06-04-2015, 03:24 PM
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MMK110464
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Originally Posted by mgordon18 View Post
While driving last week, my 2006 S 6MT started mildly bucking under acceleration. It's the kind of bucking that happens when you're first learning to drive stick, you know, and you don't let the clutch out exactly right? It's like that but much milder, but you could definitely feel it. Another way to describe it is it's like coming off and on the throttle a touch.

The car would do this not only coming off the line, but out on the highway as well. I'm in 5th gear, 3200rpm, and give it a little gas to speed up a bit, and the bucking would start. As soon as I let up off the accelerator, it would smooth out. Back on the accelerator and it would start again.

As I drove the 60 minutes to my destination it went away completely, and didn't show up again on the way home. The drive home was 4 hours later, so the engine started off cold.

Any idea what this could have been? Scared the crap out of me when it was happening, but the it disappeared...

Thanks in advance,
Mike:
take a look at this 2 discussions:

https://rennlist.com/forums/991/7072...1-base-mt.html

http://www.6speedonline.com/forums/9...-2500-rpm.html

I hope this helps.
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Old 06-04-2015, 04:00 PM
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Originally Posted by MMK110464 View Post
Thanks for the links MMK, but I think what I have is different. Those links describe a single "dead-spot" hesitation on the way up the RPM range. My issue was happening all over the rev range whenever I gave it gas. And it wasn't a single hesitation, it was multiple surge/relax/surge/relax until I lifted my foot to let the car coast. I tried it in different gears and different speeds.

Those threads seem similar in that none of the hesitations were violent, but they were definitely noticeable. They started off feeling similar to the bucking that happens when a novice clutch user cannot modulate the clutch and throttle properly at startup, but over the course of about 10 minutes, slowly eased up and went away. There was no noticeable RPM drop and no audible changes that I could discern.

I'm headed to my mechanic tomorrow morning for an oil/brake fluid change. I'll ask him his thoughts. Not sure it will be repeatable, but we'll see.
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Old 06-04-2015, 04:33 PM
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Did the bucking only happen under mild acceleration but go away under either normal cruise *you said "yes") or heavy acceleration (you didn't say)? My son's Audi has a somewhat similar phenomena happening only under mild acceleration. It turned out to be a loose motor or transmission mount (I forget which). With no significant acceleration there wasn't enough torque to move the engine/tranny away from its resting position. Under heavy acceleration it would peg all of the way to the other end of the mount or bolt. Only under mild acceleration would it find a sweet spot where it would oscillate back and forth.

Could it be the engine mounts at the back of the engine carrier? If you remove the air box you can visually inspect them fairly easily. Even without removing the airbox you can get someone to gun the engine at idle while you watch with the deck lid open and see if it appears you are getting excessive play. The transmission also has mounts but I don't know how hard it is to inspect them.

This is all just a wild-*** guess in the absence of other suggestions, so sorry if it sends you on a wild goose hunt.
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Old 06-04-2015, 06:52 PM
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Mike,

I'm not sure what the final verdict was but they replaced my engine no questions asked in about 3 days.

Your problem sounds exactly like mine….exactly!

I would keep noticing this hesitation that came and went and it happened at speed (highway too) but not always and at all different speeds. They started by telling me it must be the gas but I knew that wasn't it. My tech took my car home for the weekend and told me he noticed that one side of the car was very sooty above the exhaust and there was some kind of a valve problem.

They replaced that engine immediately and the car only had 4,000 miles on it.

That's what happened to me Mike and it might not be at all what's going on with yours but see what they say. If you want to call me you can and I'll send you a PM with my number just let me know. I can probably get my tech to speak with you as well but I'm in Florida now n to NJ so I'd have to coordinate that.

I'm sure he'd remember exactly what it was.

Good Luck.

Tom
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Old 06-04-2015, 07:08 PM
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mileage ? everyday driver? old gas? any work done on the car lately ? was it raining that day ? put a pro scan tool on it .it sounds like a miss fire issue which can be caused by many problems ......fuel,ignition ,sensors etc. i would hold off on replacing the engine just yet lol
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Old 06-04-2015, 07:17 PM
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Originally Posted by extanker View Post
mileage ? everyday driver? old gas? any work done on the car lately ? was it raining that day ? put a pro scan tool on it .it sounds like a miss fire issue which can be caused by many problems ......fuel,ignition ,sensors etc. i would hold off on replacing the engine just yet lol
Brilliant!
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Old 06-04-2015, 09:17 PM
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Mgordon18.

Did you experience the check engine light sometimes would turn on during warm up at idle? Mine did that about every 2 weeks. I would check the engine fault codes and it would be misfire on all cylinders. I changed the spark plugs. and all OEM spark plug could. That was at 57000 miles.
The problem of misfires stopped for a while and are now back, only if you let it idle and not giving car a little gas.
Now I have noticed the same condition you are experiencing and while driving in sport mode, it is more noticeable. I also know that it happens when I shift from 2nd to 3rd,but am being lite on the gas pedal. When I am getting on it, and not lite of gas, it does not happen.
I would make sure you are not driving it too casual or as I caught myself as being lazy..
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