weird revving and rough idle

[a4_boi]

It all happened while I almost arrived to work. And now it suffers really rough idle with no CEL.

If I press and release the gas pedal, sometimes the engine would just go back to rough idle or sometimes it wouldn't go back to idle and keep the revving upto 2000rpm for about 5~10 sec. And then back to rough idle mode

It started to act like this right after I got off the hwy. I also felt the engine lost the power.

Can anyone please tell me what's going on? or any similar experience?

coil pack issue?

[inaforest]

kinda sounds like it.

[wolfdog]

When's the lats time you checked the gap or replaced on your plugs?

[diagnosticator]

It's not possible to accurately predict what the problem is, without a diagnostic scan for the relevant trouble codes that will point to the cause of the symptoms. Get a scan and post back the codes.

[gear_head81]

its a mis-fire, check your plugs and or do a scan to find out which coil pack is miss firing.

[aaaudiprotein]

I think in 99% when the coilpack(s) goes bad you get a CEL
Spark Plugs- maybe
Running lean= vacuum leak- possibility + but with this kind of misfires you should've had a CEL, unless you drove with that for 5 min or so.
What about a bad throttle body?

[aaaudiprotein]

And yeah, better scan it to see what causes that

[a4_boi]

OK, here is the follow-up:

I went to the stealer (yeah, I shouldn't go there. But I am in a new neighborhood and all independent Audi shops are too far away from my place). Since there was no CEL, they took 3 hours to figure out the issue: 3 dead coilpacks.

But both me and stealer have the same question about my car..... how come there wasn't any CEL??? Anyone has a theory about this?

Moreover, the stealer is STEALER. They want to screw me over by claiming my rear coolant flange is bad and it needs to be replaced. They quote me: $630!

I paid for the CP fees but for coolant flange ..... forget the stealer, I am heading to indep. audi shop for dat. :(

[a4_boi]

sidenote: time to buy CP and store them in trunk :(

[aaaudiprotein]

Did u replace them yourself?

[inaforest]

Where in CA do you live? What dealership did you go to?

[diagnosticator]

OK, here is the follow-up:

I went to the stealer (yeah, I shouldn't go there. But I am in a new neighborhood and all independent Audi shops are too far away from my place). Since there was no CEL, they took 3 hours to figure out the issue: 3 dead coilpacks.

But both me and stealer have the same question about my car..... how come there wasn't any CEL??? Anyone has a theory about this?

Moreover, the stealer is STEALER. They want to screw me over by claiming my rear coolant flange is bad and it needs to be replaced. They quote me: $630!

I paid for the CP fees but for coolant flange ..... forget the stealer, I am heading to indep. audi shop for dat. :(

Couple of reasons for no CP related DTCs,
The coilpacks are not monitored directly by the ECU, The ECU only checks for +Batt VDC is present or too low. The detection of misfires is by the dip in crankshaft angular velocity coincident with the power stroke of the cylinder involved, and the misfire recognition will turn the CEL ON only after the number of misfires exceeds the threshold count.
The misfire recognition may also be disabled, if the ECU can't perform the Misfire recognition analysis accurately for some reason.

[wolfdog]

^^^ wow, awesome. I love learning.

The rear coolant flange is a DIY... a pain in the ars but a DIY nonetheless.