Idle Misfire

[Ob3R]

Hey there Audizine, I've been around for a while but never post very much. I have searched for answers in various forums and I just don't get a clear answer so I thought I would ask.
I have a 2000 Audi S4 6 Speed. I have a problem with an Idle misfire. The misfire is ONLY at idle. WOT is strong and pulls as I believe it should.
I get the following codes: Multiple/Random Misfire, Cylinder 1, Cylinder 4, Cylinder 5 Misfires as well as Internal Resistance Too High: Sporadic on both Sensor 1 Oxygen Sensors on both Banks. Secondary O2 sensors are deleted as I am Stage 2.

I have also noticed that the RPM needle slightly moves up and down in idle as well and never sits in the same place.

The problem I am having is that I only get misfires on those cylinders. I also have replaced the O2 sensors once already. Could these also be bad? They are genuine O2 sensors. Could it possibly be a boost or vacuum leak because of the RPM needle moving around?
I have moved around the coils and plugs have only 1000 miles on them. I have a 2.0 Conversion as well. Compression is good as well as I tested that.

Any input in which direction I should go would be great. Thanks in advance!

[getslideways]

Is this a new problem, an old original problem? Did this appear only after changing something? I know you mentioned swapping plugs, what gapping are you running on them?

Boost leak test is a very good idea.

The primary O2 sensor needs to be addressed first and foremost, as without those being able to tell the ECU what is going on, it makes the ECU's job more difficult. (why were these originally replaced? Just age or were they throwing the same resistance codes?)

What 2.0 conversion harness are you using? Have you tried swapping adapters or harness sides? (if this problem existed prior to the 2.0 conversion then this likely wont uncover anything new)

Any change when unplugging the MAF? What are your long term fuel trims? You can also try swapping injectors to see if the problem follows if nothing else helps narrow down the suspects, however failing or clogged stock injectors seem to be pretty rare on this platform.

Did you have the problems prior to the "Koya Tune"?

[Ob3R]

Is this a new problem, an old original problem? Did this appear only after changing something? I know you mentioned swapping plugs, what gapping are you running on them?
They are the stock Copper NGK so whatever they come with is the gap that I kept.

Boost leak test is a very good idea.
Will do that this week then!


The primary O2 sensor needs to be addressed first and foremost, as without those being able to tell the ECU what is going on, it makes the ECU's job more difficult. (why were these originally replaced? Just age or were they throwing the same resistance codes?)
Just because of age and because I put in catless downpipes so though I might as well change them out. I guess I can salvage a used set that work and see if those work better without codes.

What 2.0 conversion harness are you using? Have you tried swapping adapters or harness sides? (if this problem existed prior to the 2.0 conversion then this likely wont uncover anything new)
I got it from a fellow member. It was a problem before this but though maybe changing to the conversion might fix it. I'll try to swap out the adapter just to see.

Any change when unplugging the MAF? What are your long term fuel trims? You can also try swapping injectors to see if the problem follows if nothing else helps narrow down the suspects, however failing or clogged stock injectors seem to be pretty rare on this platform.
Havent tried unplugging MAF, will do that today and see since I have the bosch one.
I'll also log and look at the fuel trims and post them up.
Are the injectors easy to get to in the 2.7? Never tried to do anything with them on this particular engine.

Did you have the problems prior to the "Koya Tune"?

Yes i did. I had it stock, it was the same. I had an APR tune, it was the same and still is the same with the custom tune now too.

[vavJETTAw36]

Injectors are easy to do if youre not using the same hose clamps in some areas. If you are using crimp oem hoses, it could take awhile.

Make sure you buy oem replacement injector seals as you will need them.

Pull off accordion, y pipe, unplug n75 and pull it and the rubber grommet off of the fuel rail assembly (grommet has the hose running to the spider passing through it. Grommet will pop out of its retaining hole). Then uhook the fuel lines. Unhook the f hose (if you have one), and then there is a sensor that's hooked to rubber on the ride side of the fuel rail. Pull it out of the rubber and swing it out of the way. You'll have to unhook it from another hose I cannot recall but it's obvious. Pull vac line off fuel regulator. Pull vac hoses from left and right side that run parallel to the inlet pipes. Now ready to unbolt rail. Unbolt rail. I recommend un clipping the injectors from the rail as it will make removal easier. Then pull up from the left side and ride side while being careful not to bend the rail. It's pretty strong but just be careful. Most of your time will be trying to release the rail from the injectors.

Tips:
Take a pic of injector harness and clip orientation. For that matter snap a picture of the whole vac setup just in case you forget.




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[Ob3R]

Awesome. If it comes to checking the injectors then i have a clear idea of what to do.
Many thanks to you, vavJETTAw36

Sent from my .:R32

[christianb5s4]

Does anyone have the part number for the OEM injector o-rings by chance?

[CtS4Driver]

I could use this info as well...


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[vavJETTAw36]

I always check Ecs tuning for this. They'll have part numbers in the listing.


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[christianb5s4]

Here's the part, part number is 035906149A:

https://www.ecstuning.com/Audi-B5_S4...ors/ES2765685/

[vavJETTAw36]

Here's the part, part number is 035906149A:

https://www.ecstuning.com/Audi-B5_S4...ors/ES2765685/

Thats it. Ive used the elring on two separate occasions with no leaks. the 12 pack is 11 bucks cannot beat it. I refuse to pay the 1.73 per bosch. or outrageous price of $6 for VW/AUDI

[christianb5s4]

Thats it. Ive used the elring on two separate occasions with no leaks. the 12 pack is 11 bucks cannot beat it. I refuse to pay the 1.73 per bosch. or outrageous price of $6 for VW/AUDI

Europaparts has them for $0.88 each (Bosch), I just posted ECS since they're a vendor!