3.0 Random misfires after timing belt replacement

[12GaugeRage]

I just did a timing belt replacement along with water pump, thermostat, front main seal, tensioners, two vacuum lines (the brittle plastic ones), and power steering hose. I drove it fine the first day about 3 miles round trip. Today after about 2 miles OBD threw a random misfire code along with misfires on 5 cylinders. It's idling a little rough around 760rpm when before it would sit around 800rpm. Still drives OK outside of idle.

Any ideas on what to check first? I have a VCDS cable coming in the mail as well, should I wait for that to arrive before doing anything else?

[2004a4b630QT]

Sounds like a vacuum leak. Check your vacuum lines. Make sure you didn't break any of the connection points or leave anything unplugged. Also try swapping ignition coils to see if the misfire is coil related or not. The 3.0 coils are a failure point. Check for oil in spark plug well too for cyl5.

[12GaugeRage]

It's 5 different cylinders, not just cyl5. I'll double check my vacuum work, maybe it worked loose after running. If it makes any difference I filled the gas tank with 93 Oct right before the check engine light. Does anyone know if I can use VCDS to narrow down the issue if my vacuum lines aren't the problem?

[2004a4b630QT]

Yeah you can use it check your timing. I'm not sure which measuring block but it's been mentioned more than once on the forum

[imnuts]

You can check the cam angle/phase with VCDS to see if timing is normal. You could also check the air/fuel ratio just to make sure it isn't running lean.

Sent from my Pixel 3 XL

[walky_talky20]

^ I second this. Check cam phase with VCDS. On the 3.0, I like to check it after I'm done with the t-belt regardless, just to make sure it's all in spec.

[jj94tt]

I had a random cylinder misfire problem that went away (knock on wood) when I replaced gaskets during an intake refresh. I don't remember if the intake manifold comes off during a t-belt job, but if so, I wouldn't reuse gaskets.

Also, this has been discussed before, but if the intake changeover valve is not working properly, maybe that could be contributing to your problem.

I am not exactly sure what fixed it for me because I did all of the following:
new changeover valve
new plugs
cleaned injectors with new o-rings
new tb gasket
new manifold gaskets
cleaned manifold ports
new valve cover gaskets

*note* did NOT replace any coils

[WerkzINC]

I just went through the same exact issue and drove me insane. couldn't figure it out for 2 months until literally this weekend found one of the vacuum lines that I believe went to the PCV and one of the brittle plastic tubing that go to the PCV off the back of valve cover cracked so slightly that you couldn't hear it or see it . Would cause a random misfire code that would only go flash when cruising in gear and letting off the gas. and when coming to a stop the idle would drop ever so slightly than go back up..Had the same symptoms and thought I had the timing off a tooth and didn't want to redo it . when removing the valve covers the lines are so brittle . So yeah hopefully that's your issue also..... good luck

[12GaugeRage]

I had a random cylinder misfire problem that went away (knock on wood) when I replaced gaskets during an intake refresh. I don't remember if the intake manifold comes off during a t-belt job, but if so, I wouldn't reuse gaskets.

Also, this has been discussed before, but if the intake changeover valve is not working properly, maybe that could be contributing to your problem.

I am not exactly sure what fixed it for me because I did all of the following:
new changeover valve
new plugs
cleaned injectors with new o-rings
new tb gasket
new manifold gaskets
cleaned manifold ports
new valve cover gaskets

*note* did NOT replace any coils

I did replace the gaskets on the timing covers, intake manifold didn't come off. I'll have to look into that intake manifold valve and how to tell if it's working correctly, thanks for the heads-up.

[12GaugeRage]

I just went through the same exact issue and drove me insane. couldn't figure it out for 2 months until literally this weekend found one of the vacuum lines that I believe went to the PCV and one of the brittle plastic tubing that go to the PCV off the back of valve cover cracked so slightly that you couldn't hear it or see it . Would cause a random misfire code that would only go flash when cruising in gear and letting off the gas. and when coming to a stop the idle would drop ever so slightly than go back up..Had the same symptoms and thought I had the timing off a tooth and didn't want to redo it . when removing the valve covers the lines are so brittle . So yeah hopefully that's your issue also..... good luck

I did replace two brittle plastic lines. The first ran from a T split next to the power steering pump and ran along between the intake manifold and the timing cover and came up underneath the vacuum system tray and connected to a T fitting between the check valve and another part. The second one I replaced ran from the same T fitting by the power steering pump and behind a plate that attaches to the block underneath the camshaft gears. That one connected to a line near the power steering reservoir behind the driver side headlight. I double checked both of those replacements, I'll make sure to triple check them again.

It seems to drive fine whenever I'm moving. I noticed today that it was having a bit of trouble starting, though I don't remember if it was from a cold start or not. I'm planning on dropping by a parts store and having the battery checked.

[Turbo510]

When I bought my 3.0 used, right away it had a couple of driveability problems; one was a sudden temporary lessening of torque, as if I was letting up on the throttle when I wasn't doing that. That was the brake light switch going bad.

The second was similar to what the OP describes; I would call it a surging, which may have resulted in misfire codes. I'm not sure because away from my notebook now. That was caused by a failing crankcase pressure control valve.

[euronyc]

codes?

[12GaugeRage]

codes?

The first time was p0300, p0301, p0302, p0303, p0304, p0306. That was the second start after reassembling the engine, engine was warm. After clearing codes it came back as p0300, p0301, p0302, p0303. That was the 4th start, engine was warm. I haven't driven it since. I suspect it's on startup since the first time it would detect a random misfire it wouldn't throw a CEL, but it would the second time. I'm planning on driving it around some more later today and setup my VCDS cable and get more detailed info, I'll post here when I have more information.

[12GaugeRage]

When I bought my 3.0 used, right away it had a couple of driveability problems; one was a sudden temporary lessening of torque, as if I was letting up on the throttle when I wasn't doing that. That was the brake light switch going bad.

The second was similar to what the OP describes; I would call it a surging, which may have resulted in misfire codes. I'm not sure because away from my notebook now. That was caused by a failing crankcase pressure control valve.

I'm not having any driveability issues, i did a few 2nd gear pulls and it felt good. I had planned to getting around to checking the PCV in the future anyways in an effort to reduce oil consumption, maybe I should bump that up in priority.

[12GaugeRage]

Sunday,28,April,2019,00:10:02:32302
VCDS -- Windows Based VAG/VAS Emulator Running on Windows 10 x64
VCDS Version: 18.9.1.0 (x64) HEX-V2 CB: 0.4437.4
Data version: 20190114 DS296.0
www.Ross-Tech.com


VIN: X License Plate:


Chassis Type: 8E (8E - Audi A4/S4/RS4 B6/B7 (2001 > 2008))
Scan: 01 02 03 08 09 0F 11 15 16 17 18 25 36 37 45 46 55 56 57 65
67 69 75 76 77

VIN: X Mileage: 262300km-162985miles
-------------------------------------------------------------------------------
Address 01: Engine Labels: 06C-909-559-ASN.lbl
Part No SW: 8E1 909 559 B HW: 8E0 909 059 A
Component: 3.0L V6/5V G 0030
Revision: 00000000 Serial number: AUZ6Z0D0235028
Coding: 0013711
Shop #: WSC 63351 000 00000
VCID: 3537205BF956944F7DB-5160

7 Faults Found:
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 008 - - Intermittent - MIL ON
16685 - Cylinder 1
P0301 - 008 - Misfire Detected - Intermittent - MIL ON
16688 - Cylinder 4
P0304 - 008 - Misfire Detected - Intermittent - MIL ON
16687 - Cylinder 3
P0303 - 008 - Misfire Detected - Intermittent - MIL ON
16686 - Cylinder 2
P0302 - 008 - Misfire Detected - Intermittent - MIL ON
16690 - Cylinder 6
P0306 - 008 - Misfire Detected - Intermittent
16689 - Cylinder 5
P0305 - 008 - Misfire Detected - Intermittent
Readiness: 0010 0001

-------------------------------------------------------------------------------
Address 03: ABS Brakes Labels: 8E0-614-517.lbl
Part No: 8E0 614 517 A
Component: ABS/ESP allrad 4529
Coding: 04495
Shop #: WSC 06435
VCID: 2615F71731F0EFD7C41-51CE

1 Fault Found:
01826 - Sensor for Steering Angle (G85); Supply Voltage Terminal 30
35-10 - - - Intermittent

-------------------------------------------------------------------------------
Address 08: Auto HVAC Labels: 8E0-820-043.lbl
Part No: 8E0 820 043 AD
Component: A4 Klimaautomat 1424
Coding: 00000
Shop #: WSC 63351
VCID: 6393AE0302425AFFE3F-513C

1 Fault Found:
00819 - High Pressure Sensor (G65)
30-00 - Open or Short to Plus

-------------------------------------------------------------------------------
Address 09: Cent. Elect. Labels: 8E0-907-279-8E2.lbl
Part No: 8E0 907 279 F
Component: int. Lastmodul RDW 0517
Coding: 00011
Shop #: WSC 00000
VCID: 3537205BFC56944F7DB-4B00

1 Fault Found:
01800 - Light Switch (E1)
27-00 - Implausible Signal

-------------------------------------------------------------------------------
Address 0F: Digital Radio Labels: 8E0-035-593-XM.lbl
Part No: 8E0 035 593 A
Component: SDAR XM 0010
VCID: 270BFA1336CAF6DFFF7-5066

1 Fault Found:
02635 - Tuner Not Enabled/Activated
35-00 - -

-------------------------------------------------------------------------------
Address 15: Airbags Labels: 8E0-959-655-84.lbl
Part No: 8E0 959 655 K
Component: Airbag 8.4EP 1001
Coding: 0010607
Shop #: WSC 63351 000 00000
VCID: 3FDB4273CB6A5E1FA77-5184

No fault code found.

-------------------------------------------------------------------------------
Address 16: Steering wheel Labels: 8E0-953-549.lbl
Part No: 8E0 953 549 N
Component: Lenksáulenmodul 0611
Coding: 02041
Shop #: WSC 63351
VCID: 3E253F77C9605717AC1-4B00

No fault code found.

-------------------------------------------------------------------------------
Address 17: Instruments Labels: 8E0-920-9xx-8E2.lbl
Part No: 8E0 920 950 P
Component: KOMBI+WEGFAHRS. RB4 D42
Coding: 01231
Shop #: WSC 11264
VCID: 36352757E1509F57741-5160
WAULT68E95A043287 AUZ6Z0D0235028

No fault code found.

-------------------------------------------------------------------------------
Address 36: Seat Mem. Drvr Labels: 8E0-959-760.lbl
Part No: 8E0 959 760
Component: Sitzmemory R2 F 0F04
Coding: 00002
Shop #: WSC 63351
VCID: 71BFD44BC88EF86F613-4B3C

No fault code found.

-------------------------------------------------------------------------------
Address 46: Central Conv. Labels:. 8E0-959-433-MAX.clb
Part No: 8E0 959 433 BB
Component: Komfortgerát T7B 1612
Coding: 11788
Shop #: WSC 63351
VCID: 72BDDB47CDB8C377989-4B00

Subsystem 1 - Part No: 8E1959801
Component: Tõrsteuer.FS BRM 0205

Subsystem 2 - Part No: 8E1959802E
Component: Tõrsteuer.BF BRM 0205

Subsystem 3 - Part No: 8E0959801A
Component: Tõrsteuer.HL BRM 0205

Subsystem 4 - Part No: 8E0959802A
Component: Tõrsteuer.HR BRM 0205

2 Faults Found:
00962 - Alarm via. Tilt Sensor
35-00 - -
00955 - Key 1
35-10 - - - Intermittent

-------------------------------------------------------------------------------
Address 55: Headlight Range Labels: 4Z7-907-357.lbl
Part No: 4Z7 907 357
Component: dynamische LWR D09
Coding: 00060
Shop #: WSC 63351
VCID: 04518D9FE73CFDC7BA5-4B3C

1 Fault Found:
00776 - Level Control System Sensor; Left Front (G78)
31-00 - Open or Short to Ground

-------------------------------------------------------------------------------
Address 56: Radio Labels: 8E0-035-1xx-56.lbl
Part No: 8E0 035 195 H
Component: symphony II PM6 0410
Coding: 01205
Shop #: WSC 26112
VCID: 2C01053F2F2CD587125-5066

No fault code found.

End----------(Elapsed Time: 05:15, VBatt start/end: 12.2V/12.1V)-----------

This is what VCDS gave me. I drove it about an hour total today with no performance problems. I'm still in the process of learning how to check my timing using VCDS, if anyone knows of quick how to for the 3.0 that would be awesome.

[12GaugeRage]

I took the car on a road trip yesterday to go see a race, 4.5 hours each way. Before I left I cleared the codes using a bluetooth OBD-2. After 9 hours of driving and multiple stops for gas and food it didn't throw a CEL once. Maybe the issue resolved itself? The only things I did to prepare for the trip is to double check that the vacuum lines were attached and added a half quart of oil.