Cagri

Hi everyone,

My car is Audi S5 4.2 V8 - 2010 with 160.000 km.

It's been months I'm trying to fix this issue but still car is not working smooth at idle. I've done all below maintenance but still the problem exists, please share if you've any experience on anything else and I can have a look;

* Ignition coils replaced,
* Spark plugs replaced,
* Injectors replaced,
* Engine mounts replaced,
* Transmission mounts replaced,
* Alternator bushes replaced,
* Compressor replaced,
* Radiator replaced,
* Catalytic converters removed,
* Transmission oil & filters replaced,
* Engine oil & filters replaced,
* Steering fluid replaced,
* EGR valve replaced,
* PCV valve replaced,
* Intake manifold cleaned,
* Smoke test is done, no leaks
* Valve cover gaskets are replaced,
* Intake gaskets are replaced,

There's no fault code in the engine, only P0036 H02S Heater Control Circuit Bank 1 Sensor 2, happened after cat delete process, probably an issue on wiring or mechanical fixation but since they're not working after cat delete anymore, shouldn't be an issue (open for comments)

Car is working under stress in idle, RPM is steady, only when both fans are working, second fan is opening and RPM goes to around 800 and shaking increases.
Also when I increase the RPM in idle, there's a vibration also at around 1900 RPM, below or above, it disappears.

I've some oil leak on the primary engine block, since it's a big job, I don't touch it. Every 10.000 km, max 2 liters oil I add, nothing more.

On top of everything, there's a constant coolant leak, we checked the car, there's no visible leaks. There's no bubbling in the coolant tank, no milky engine oil cap, no white smoke (considering if the issue is head gasket).

I don't really know what should be the next? What else I can check in this car? There's no misfiring, no RPM fluctuation, no stalling, no code, nothing. But the car is not working healthy and silent.

Fuel trims are normal (only around -7 at Bank1, Bank2 is almost 0).

MPG is normal, even better after injector replacement.

I'm thinking about torque converter because regardless the gear (P,D,N,R whatever), there's a ''whizzing sound" increasing/decreasing parallel with RPM. Mechanic told me it's normal, but maybe there's something wrong in transmission?

Gear shifting is not perfect but very smooth especially car gets warmer.

Acceleration: 0-100 km 5.5 secs, 0-200 is around 18 secs, looks very normal.

As soon as you accelerate, car smooths out but whenever I stop at signals or something, vibration starts. With AC on, it's worst as I mentioned above.

Kindly waiting for your comments and ideas, what can be the next? What can be the problem?

ecgarzone

It appears that you've covered all the bases, and several that in no way that would affect rough idle, like brushes in the alternator. Be advised, alternators do not have brushes. What I see, or don't see, in your completed list, short of a bad light bulb, (Sorry, I had to add some humor to your frustrating problem) is a compression test. My opinion is the problem may be attributed to a leaking or burnt valve or valves, or a blown head gasket, which would account for the loss of coolant. In addition, since the engine appears to smooth out as rpm increases, that's not unusual since the sympton is merely masked at higher RPMs. Recommend you do a compression check. There should be no more than 10% difference in the cylinders. If compression is low between two or more adjoining cylinders, generally the head gasket is blown. If the compression is low on only one or more non-adjoining cylinders, it's most likely a carbon/valve issue.

Cagri

Thanks for the reply and I agree with your humor, there was some processes which has nothing to do with rough idle but I just wanted to list all history.

First place told me that they've done the pressure test in the cylinders and there was nothing wrong, I relied on this answer and started checking other components but after finding out they did such a bad job on other parts, i will repeat the cylinder pressure test again.

Tomorrow I'll start checking coolant system first under pressure, to make sure there's no leak in hoses, and then cylinder pressure test will follow.

There was some carbon build up in the engine but wasn't too dramatic, so let's see. Failing head gasket doesn't sound pocket friendly unfortunately but if this is gonna fix the issue, I'll go for it.

Again thanks for your reply!