random bucking/hesitation

[wstpride92]

So i have owned my 08 s4 for almost a year now. I've noticed over time that the car seems to buck when slowly accelerating at low RPM's. It sort of feels like a misfire. It happens under 3k rpm. It used to buck only once then clean up but now on occasion i can get it to do it a few times in a row. If i floor it i don't feel it happen, only seems to be a part throttle thing. If i am on the highway in 5th or 6th and want to speed up i will usually feel the hesitation then it start going. The annoying thing is the car wont throw a CEL. I changed the spark plugs this weekend but that hasnt helped. It is starting to drive me nuts. The car has 48k miles and mods are 2.25" miltek exhaust and K&N drop in filter. I've had a similar issue in a 1.8t jetta i had with hesitation at part throttle, turned out to be a bad MAF, but i am not convinced thats what it is in this car. What should i look at.

[verymickey]

lemme know what you find out.
mine does the same thing, but i just chalked it up to the car not wanting to go slow...

[JS4Avant]

Did you change the coil packs?


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[gaben2racin]

Vacuum leak

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[S4orgy]

Is your car an automatic?

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Maybe a mount

[wstpride92]

Car is manual. i have not changed coil packs. I don't want to buy 8 new ones if i am not positive it will fix the issue. maybe i can buy one and move it aorund to different cylinders to see if it makes a difference. ive looked for vacuum leaks but havent found any, but i'll check again.

[924Carrera]

I started a thread about this a while back since I am having the same issue, with brand new plugs and coil packs. Logging with VCDS showed the issue was the throttle plate rapidly opening and closing at the edge of the EPC pedal range. However, it seems unusual to have this kind of behavior. I suspect a vacuum leak on my car as well as I am having random shuddering at idle only, but haven't had a chance to try to track that down yet.

[wstpride92]

I started a thread about this a while back since I am having the same issue, with brand new plugs and coil packs. Logging with VCDS showed the issue was the throttle plate rapidly opening and closing at the edge of the EPC pedal range. However, it seems unusual to have this kind of behavior. I suspect a vacuum leak on my car as well as I am having random shuddering at idle only, but haven't had a chance to try to track that down yet.

Has your car thrown any CEL. I wish mine would so i would have a direction to investigate.

[924Carrera]

Has your car thrown any CEL. I wish mine would so i would have a direction to investigate.

Yeah, mine has not, which is why it's so weird. Based on the parameters I logged, it seemed like it was working correctly, but it feels extremely unrefined and I also don't remember it happening previously. Also, I have a B5 which also has EPC and it never does that.

[q_dubz]

mine does it too! especially around 2.5k in 2nd

[wstpride92]

i don't think its normal. I mean these are expensive luxury cars. For what they cost brand new i highly doubt this is normal.

[jakeoboy67]

have you tried resetting the throttle body ?

[JimmyBones]

Make sure that the 5 mm Allen bolts for the intake manifold are tight (11 Nm) and start in the middle then criss-cross your way towards the outside edges. Also make sure that the intake boot between the mass air flow sensor to the throttle body is on tight. Especially at the throttle body side because it likes to come loose.

[924Carrera]

Make sure that the 5 mm Allen bolts for the intake manifold are tight (11 Nm) and start in the middle then criss-cross your way towards the outside edges. Also make sure that the intake boot between the mass air flow sensor to the throttle body is on tight. Especially at the throttle body side because it likes to come loose.

Good tips that might help OP. However, my car was doing this thing before and after I did the valley pan job, in the process adding loc-tite to the IM bolts and definitely securing the MAF tubing. Made no difference, the car resumed the weird behavior immediately.

[kevinye77137]

Have you tried cleaning the MAF? Clean the throttle body end links maybe semi stuck?

[ImAudiHeree]

I'm going through this on my car as well still no resolution in sight driving me nuts going to take it into an indy shop and see if they can smoke test for vacuum leak.

[924Carrera]

Have you tried cleaning the MAF? Clean the throttle body end links maybe semi stuck?

Cleaned both the MAF and throttle body on mine, no difference.

[gaben2racin]

Bad fuel filter?
Or pump?

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[924Carrera]

Bad fuel filter?
Or pump?

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New fuel filter on mine. Haven't replaced the pump, but I find it odd that it would not exhibit any other typical failing pump symptoms.

[gaben2racin]

Have you checked your injectors?

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[924Carrera]

Have you checked your injectors?

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What kind of check would you suggest? They are all seated and the car isn't misfiring, but I suppose they could still have an issue of some kind.

[gaben2racin]

Plugs loose

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[924Carrera]

Plugs loose

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I do have 2 injectors that sheared their locking lugs off for the plug (wonderful design....). I assumed that if the car wasn't misfiring, then the plugs were seated correctly, but perhaps I should go buy a pair of new injectors.

[gaben2racin]

Well if I was working in Portland I would come n give you a hand.
Trying to help you trouble shoot on here doesn't really help much

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[924Carrera]

Yeah it's tough. I've delved into it and came up empty handed other than seeing the pedal input and throttle body response and the "flutter" happening at the edge of the pedal range.

[ladiesgod]

Mine was bucking. It ended up being a vacuum leak.

I still get the flat spots and loss of acceleration/power. I think it's pointing to clogged downpipes/cat