S4 B5 cold start problems and rough idle after warmup

[rnagy86]

Hello,

After I've spent several hours on the forum trying to find a fix for my issue and after throwing a lot of money into it I decided to open a new topic so that it might help finding the fix for my problem.
My current setup is an APB engine, K04s, Aeromotive 340 FP (stock one went bad and my friend had this) , 4bar FPR, stock injectors, Forge FMDV008 DVs, K&N air filter.

I've two ECUs, one running the stock program and the second one is modified for my setup, but that does not really seem to matter because the issue that I am going to describe happens with _both_.

So on cold startup (not all the time) my RPM goes up to 1800-2000 rpm then drops down to 1200, and then after 2 seconds the engine starts to splutter really bad like I have serious misfires. It seems to me that
the mixture is really crap at this point. While this is happening, the rpm is jumpoing between 1300 and 700 and that makes the turbos to spool up which makes the issue even worse and the car is shaking really bad.

After about 15-20 seconds the issue starts to slow down and the rpm sticks to 1200 rpm and from there everything is as usual, it takes about 5 minutes for the car to warm up properly and then
the rpm drops down the the normal warm level, and from there it only jumps between 780-830 rpm.
According to my logs I have about 5-8 misfires a minute randomly on all 6 cylinders, but it does not happen on more than one at the same time.
Other than that, the car drives totally fine and it pulls as hard as it should without stalling or misfiring.
The other thing that I noticed is that If i shut the engine down right when the rpm starts to jump around, and then I restart it, the issue does not happen.

I only use 95 or 100 oct. fuel.

What we have tried already to fix the issue:
- replaced spark plugs gapped to 0.7 mm with the ones it had in it already (FR7KPP33+)
- replaced spark plugs gapped to 0.7 mm with a different one (NGK PFR7Q)
- replaced all six coil packs
- replaced both of the ICMs
- replaced engine coolant temperature sensor
- replaced FPR (fuel pressure is 4.0-4.1 bar)
- replaced fuel pump relay
- checked for boost and vacuum leaks with a leak tester (no leaks at all)
- replaced the Bosch MAF with a new one
- checked all O2 sensor values and they are all in range
- checked EGT sensors

I would love if someone could throw some ideas before I light the car up on fire.

Thank you

[JoBuNY]

I had the same issue when I had my S4 and mine was the Coolant Temp Senor (Green top) at the back of the motor. I replaced that and my cold start sputtering immediately went away.

The part was like $35 from the dealer and then I got a new O Ring for it as well (like $2). Pretty easy to replace, and if you need help this is a write up on these forums with pictures.

[rnagy86]

As i said, i replaced that with the green top one (the original was green top already) :)

[rnagy86]

Here is a small video that I managed to shoot today while starting the car:

http://www.youtube.com/watch?v=wbfLz71Hbc0

[mrandersons4man]

Just an idea but maybe a really clogged fuel filter? Pretty cheap and not too difficult to replace.

[goquattro12]

get a new maf...i had similar problems

[rnagy86]

Guys, these have all been replaced already.

[goquattro12]

try 91 or 93 octane

i duno i had b5 stage 3 a4 that did this, i just sold it.
dude who bought it said there was sumthing wih the valves and lifters

[rnagy86]

You can't get 91 or 93 octane here. The minimum you can get is 95 which I tried already. Better fuel should not fuck with the engine like this. Mh so you think it's a mechanical issue?

[goquattro12]

yea he was a mechanic and he wanted his money back so it was probably a pretty bad problem

[rnagy86]

So after doing even more logging it turns out that with my tuned ECU i am getting totally different O2 sensor voltages on bank1 that i do with my stock ECU. With my tuned ecu I always get around 0.100V or even less, but with the stock ECU I get aroun 0.600-0.800V.
The other strange thing that happens is that my idle issues start to happen at the same time when the ECU can't read any O2 sensor values from bank 1 (100 according to vag-com instead of 111 in block 030/031).
Then I go and do a full throttle in 2nd and my O2 readings comes back.
Since this does not happen with the stock ECU at all, I was wondering if there can be a wiring issue or a PIN getting loose on the ECU?

Thanks

[car_guy81]

I sent you a PM. Did you figure this out? I'm the same place you were at back in April. So frustrating! Thanks