Not Your Normal "Rev Hang"

[challenger]

Hello everyone,

I have recently noticed an issue with my car that I need some help with. I have read every forum on this possible and found no solution or anything that was exactly like my issue. If I am repeating a post I did not find or read then I appologies in advance. I do hope this will help others in the future if we can get to the bottom of this.

About 3 days ago when shifting gears, I have started to notice a "rpm hang->slow rpm drop->normal rpm drop" where the RPMs will stay at the point of shifting for a second or two, slowly decrease for a few more seconds (slower than normal), and then completely drop at the end of the RPMs as it should. This doesn't happen all the time and never on a cold start from what I have noticed. Additionally, at WOT, sometimes the RPMs jump 2-300 in-between shifts. I think this could be normal due to not releasing the gas fast enough while hard shifting but threw it in here. Now this only happens periodicly but once it starts it seems to continue happen through most gears mainly noticing it at 1-2, 2-3 and sometimes 3-4. I think its just more noticbale in the lower gears due to the larger RPM drop. Some driving sessons the car is completly normal.

Car background that could relate to the issue:
2013 Audi S4 B8.5 6MT
IE Stage 2 dual pulley e40 tune
stage 3 jhm clutch/flywheel combo (10k miles)
ecs clutch line

The only thing I changed recently are the two MAP sensors on the sides of the supercharger (https://www.fcpeuro.com/products/audi-vw-manifold-absolute-pressure-sensor-0261230234). Could this be the issue or is it more likely a faulty clutch position switch? I will be swapping the MAP sensors back to the OEM ones this weekend to see if it helps.

I have read other forums with similar issues, but my car responds differently than others:

- It does not happen just on corners
- Stability control off does not fix the issue
- I can start my car no problem with clutch depressed as usual
- I can't start my car unless clutch is depressed

I would really appreciate any insights or suggestions on what might be causing this issue and how to fix it. Thank you in advance!

I'll try to get a video of this if it helps.

[SwankPeRFection]

Why did you change out the MAP sensors? It’s possible you may have introduced a small vacuum leak if the new sensors weren’t installed properly or didn’t have tight enough seals or you weren’t careful to clean the surface before installing them. That’s pretty remote, but it is possible and it could surface as such an issue. If they are the correct part number for your car, aren’t malfunctioning and there was no install errors, it’s quite possible the ECU learning curves haven’t had time to adjust down to the new sensors, if your old ones had some readout inconsistency and the ECU was adjusting for it. If this is the case, if you have VCDS, then just go into auto scan, poll the gateway installation list and if there’s no module errors listed in red on the right, simply hit Clear Codes and confirm. This will clear the learned values and the ECU will self-adjust after that. If you don’t have VCDS, you can use your 034 flasher to clear codes (if it has this function) or if it doesn’t, simply flash back to stock and then back to your staged tune fine and it’ll do the clear as part of that process.

If none of this clears up the issue, put your old MAP sensors back in and see if the behavior is still the same. If it’s back to normal, something is up with the new sensors.

[challenger]

Why did you change out the MAP sensors? It’s possible you may have introduced a small vacuum leak if the new sensors weren’t installed properly or didn’t have tight enough seals or you weren’t careful to clean the surface before installing them. That’s pretty remote, but it is possible and it could surface as such an issue. If they are the correct part number for your car, aren’t malfunctioning and there was no install errors, it’s quite possible the ECU learning curves haven’t had time to adjust down to the new sensors, if your old ones had some readout inconsistency and the ECU was adjusting for it. If this is the case, if you have VCDS, then just go into auto scan, poll the gateway installation list and if there’s no module errors listed in red on the right, simply hit Clear Codes and confirm. This will clear the learned values and the ECU will self-adjust after that. If you don’t have VCDS, you can use your 034 flasher to clear codes (if it has this function) or if it doesn’t, simply flash back to stock and then back to your staged tune fine and it’ll do the clear as part of that process.

If none of this clears up the issue, put your old MAP sensors back in and see if the behavior is still the same. If it’s back to normal, something is up with the new sensors.

Sorry for the delay, I have experienced some other issues with my car. My motor mount must of went and lead to a cracked o2 sensor weld on the driver side. I started to hear a loud broken flex pipe sound a few weeks ago (thinking it was just my flex pipe since I know they are on there way out) and didnt have a chance to take a look at it until the other day, just assumed. I am wondering if this is causing my issue? My mount has some fluid leaking out on the driver side so this is deffinitly the reason for the crack in my test pipe. I took your advice to narrow down the issue and cleared the gateway installation list. I know you mentioned if it isnt red maybe not to but almost every one of them were read so I bit the bullet and tried it. Nothing changed. I then swapped out the MAP sensors with the orgional ones and I still have the same issuse. My last step, as you mentioned, to load my stock tune and then reload my current tune to see if this clears anything up. Same issue still persists. I am currently waiting on the test pipes to come in along with motor mounts and will swap out the o2 sensor for the sake of elimination since I will have it all apart. I will keep you posted. Thank you for your help so far!

[SwankPeRFection]

OK, if you’ve got a ton of modules listed in red on the gateway installation list, then you need to do a full auto scan and post here what the codes are. It would be extremely strange for you to have so many errors without major drivability issues. If they are however “Communication errors with module” type errors but the module still responds, then it’s a low/dying battery messing with you. It gets low while the car sits and causes problems with modules staying clear. You’d have to replace the battery, clear all your codes and then see what codes come back, if any to get a proper fresh start with trusting the VCDS scan and not chase ghosts.

Also, voltage issues could also contribute to some minor drivability issues as well, so your hang could be related to that, if the battery is to blame for all your other codes.

[challenger]

OK, if you’ve got a ton of modules listed in red on the gateway installation list, then you need to do a full auto scan and post here what the codes are. It would be extremely strange for you to have so many errors without major drivability issues. If they are however “Communication errors with module” type errors but the module still responds, then it’s a low/dying battery messing with you. It gets low while the car sits and causes problems with modules staying clear. You’d have to replace the battery, clear all your codes and then see what codes come back, if any to get a proper fresh start with trusting the VCDS scan and not chase ghosts.

Also, voltage issues could also contribute to some minor drivability issues as well, so your hang could be related to that, if the battery is to blame for all your other codes.

So I just finished my motor mounts, test pipes and PVC replacement. I decided to just install the new MAP sensors along with the third one in the back of the motor. I drove the car after all was done and I have yet to feel any rev hang. It must have been from the giant hole by my o2 sensor that I thought was a flex pipe leak. I guess I didnt think a leak in the exhaust would cause a rev hang but it seems if close enough to the o2 sensor it could trigger something odd to happen. I really appreciate your help in trying to narrow down the search. I have cleared the gateway errors and will give it some time to see what codes come back and will post my results. I just want to make sure these wont lead to other issues in the future if I have continuous faults showing up in this area.

[SwankPeRFection]

Just FYI, any errors that aren’t triggered due to driving conditions (ie chassis or defective/misbehaving sensors, etc) usually come back almost immediately after a clear and key cycle. Generally, you can clear all your DTCs, key cycle the car and start it and then do another Gateway List poll to see if anything has popped back up in any modules.