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Discussion Starter · #1 ·
So quick back story. I bought my 2009 S5 4.2 back in 2017. It had motor mount problems and a rough cold start and few other things I figure I could tackle. Fast forward its almost 2022 and I cannot get this car to start correctly. I'm going to throw out a list of what has been done and I'm curious if anyone well versed in the early V8s has any suggestions for me as I'm out of directions to go.

Let's me start by saying:

I've had the car compression tested and it's perfect. I've also had it smoke tested and it's sealed up tight.

I've had 3 carbon cleans in 25 thousand miles.

The following have been replaced:

Motor Mounts (034Motorsports)
SAI System Entirely (Pump, Hoses, EGRs)
PCV Valve
All 8 Fuel Injectors
Low Pressure Fuel Sensor
Left and Right HPFPs
VVT Sensors (Both)
Camshaft Position Sensors (Both)
Intake Manifold Gasket
Manfold Flaps
Manifold Flap Position Sensors (Both)
Throttle Body
Valve Cover Gaskets
Rear Main Seals
New Plugs (All NGK)
New MAF Sensor
New Coils (All NGK)
New O2 Sensors
Coolant Temp Sensor
Oil Lever Sensor
N80 Valve
New Alternator
New Battery
Air Filter
Catalytic Converter Recall Completed

The remaining issues are when I start the car it fires right up then dips down to around 600rpm and misses there until it slowly works its way up to the 1200 rpm cold start threshold. At this point you can smell the fuel dump at the exhaust. It lowers down to a very rough 700rpm for another 90-120 seconds and then runs fine except vcds shows a rich running condition at idle that can be felt as a small miss and smelled. Weirdly it doesn't always run badly, but it is always running rich at idle. Lots of water seems to be pouring out of my exhaust at cold start along with a black carbon/soot substance I'm guessing from the rich condition.

At this point I am going to check my fuel pressure numbers again and also consider replacing my crankshaft position sensor. Leaky injectors are possible but unlikely as they're new and replacing them had 0 effect.

If anyone can suggest a direction to go I'm truly at a loss. At this point just driving it around hoping for an insurance claim to get some money back and try on another S5 馃槶

Premium Member
3,824 Posts
Mate just a thought. In the murky world of electronics, even after a reset not everything will be as before. It could be that one sensor or chip or something has stayed "chippped" and therefore does not sing the same song as the rest of the system. I would not replace any other hardware before going thro the software and "starting again".
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