Slight Throttle Surging / Rough Running - Fixed

[walky_talky20]

Hi guys, this may be my first post on the B7 forum. I just had something I wanted to share that may help another B7 owner in the future.

Quick background: my father owns an import repair shop specializing in Audi/VW and Toyota/Lexus. I am not a mechanic, but sometimes consult with him on VCDS, diagnostics, research on pattern failures, etc.

We recently had a 2005 B7 A4 3.2 FSI Quattro Tiptronic roll in with a tricky problem.
- Engine RPM will "surge" moderately, along with a very soft misfire, especially with engine at operating temp
- Surging happens at idle, when creeping, when cruising at light load - pretty much anything other than hard accel
- Usually worse with A/C on
- Not super dangerous really, but it does pull against the brakes slightly in a parking lot or at a stop sign for example. Could lead to a mishap.
- No codes whatsoever - scanned with VCDS

Ruled out: Carbon deposits on valves
- Car accelerates extremely well and issue does not occur when cold

Ruled out: Timing issue
- No timing codes, all cam advance values in VCDS are spot on

Ruled out: Mixture issue
- Instant and Long Term Fuel trims are perfect


Initial Diagnosis: Vacuum leak or PCV issue
- Checked all the stuff, no leaks could be identified
- Crankcase vacuum is normal

Second Diagnosis: ECU Software issue possibly related to TSB 240857 2010890/8 (engine runs rough with no codes)
- Sent the customer to the nearest Audi dealer for a possible software update.
- They charged the customer $55 to tell her there were no codes (this was known) and they were unable to even attempt to fix the issue until it throws a code.

Car comes back for me to look at more in depth. Test drive reproduces problem and I'm able to park it and watch it surge and stumble.
- Can hear a weird tapping/rattling noise in the engine bay at the exact moment the revs jump around and the soft misfire occurs
- Listened with a mechanics stethoscope - tapping comes from the throttle body
- Logged throttle body with VCDS. It does seem to have erratic movement during the surging.

New Diagnosis: Faulty Throttle body
- Really not sure, though
- Re-adapt throttle body several times. Always adapts just fine.
- Find THIS THREAD with video online:


- This is EXACTLY what this customer's A4 3.2 was doing.
- I now feel better about faulty throttle body diagnosis
- Replace throttle body with used unit from a C5 A6 2.7T (shares same part number)
- Re-adapt TB, All fixed!

This one was pretty tricky to figure out due to zero codes from the ECU. It is amazing that the idle could surge like it did (sometimes 400 rpm more than it should be) without throwing any codes. Not even an "idle RPM higher than expected" code. I believe this is due to Audi significantly loosening the misfire and idle roughness thresholds in response to their issues with the FSI intake valve clogging.

Anyway, I just thought I would make a post in case somebody else runs into this. Also, I'm a little disappointed in Roth Audi in Erie PA for not taking care of this customer's concern. The throttle control on the car was acting up (a potential safety issue) and they didn't really do anything other than a $55 "thanks for stopping by" fee. I expected a little more from them.

[GearHead7]

Wow, that does sound tricky.

I have the same issue, however mine is a 2.0T FSI 6MT, I've noticed that when I do a pull or quick accelerating through 2nd-4th gear, in between my shifts my RPM will continue for a second. So if I'm at the top of 2nd gear at 4500 RPM and go to throw the clutch in and my foot is released from the gas pedal my RPM will go from 4500 to 4800... Its kinda of weird.
Im caulking mine up too the previous owner who long story short through in a cone filter and I suspect that being the reason, I would change it over just cant find the right parts for the right price. but this is good to know.

[Pillow]

Great tip! We have the same going on for my daughters A4 3.2 M6. Surges when cold in the morning and now has progressed to uneven throttle articulation going down the road. I suspect the ultra cold air temps (sub 30 last evening) are exacerbating the problem.

Ordered a used TB off Gar-Bay from a dismantler... Lets see what happens.

[lumberwood]

Wow, that does sound tricky.

I have the same issue, however mine is a 2.0T FSI 6MT, I've noticed that when I do a pull or quick accelerating through 2nd-4th gear, in between my shifts my RPM will continue for a second. So if I'm at the top of 2nd gear at 4500 RPM and go to throw the clutch in and my foot is released from the gas pedal my RPM will go from 4500 to 4800... Its kinda of weird.
Im caulking mine up too the previous owner who long story short through in a cone filter and I suspect that being the reason, I would change it over just cant find the right parts for the right price. but this is good to know.

Not sure if this is relevant anymore (been a while!) but was wondering if your clutch switch was bad... Sounds like when mine went and the rpm's would hang between shifts. Cruise stopped working too.

The OP's issue sounds more like the rpm's are revving up and more of an increase than when the clutch switch goes bad though.

Sent from my Pixel 3a using Audizine mobile app

[lumberwood]

Great tip! We have the same going on for my daughters A4 3.2 M6. Surges when cold in the morning and now has progressed to uneven throttle articulation going down the road. I suspect the ultra cold air temps (sub 30 last evening) are exacerbating the problem.

Ordered a used TB off Gar-Bay from a dismantler... Lets see what happens.

Sub'd to hear how this goes.
Been having rough cold starts too on my B7 2.0 Tip, rough idle until it warms up and even better(best) once the tranny warms. PCV done, follower, cam and HPFP good, but need to change the fuel filter and check the TB next.

Sent from my Pixel 3a using Audizine mobile app

[Pillow]

Not sure if this is relevant anymore (been a while!) but was wondering if your clutch switch was bad... Sounds like when mine went and the rpm's would hang between shifts. Cruise stopped working too.

Replaced TB with used unit. Better but not 100%. We also have the dead Cruise, so I will look into the clutch switch (IDK what it is yet).

... Probably just going to replace parts until it is permafixed. Luckily the used parts are cheap enough not to cry too badly. More to come.

Here is the short list from forum research:
- TB
- Throttle pedal
- Clutch Sensor ?
- O2 Sensors intermittent throwing an EPC code.

[Pillow]

Interesting video on the front AND back clutch switched for the B7.
https://www.youtube.com/watch?v=MpHPj0zPkwE

[lumberwood]

Interesting video on the front AND back clutch switched for the B7.
https://www.youtube.com/watch?v=MpHPj0zPkwE

If the cruise is dead, likely that one of the clutch switches is bad - it's a known symptom. If the revs are hanging or rising a bit[couple hundred rpm], but not a lot, between shifts.
Though when this happened to me, I didn't have a surging issue. Just hanging revs and dead cruise.

My comment was directed at GearHead7's post specifically but if it helps w your situation too then right on. Hope you find the cause!