Mysterious engine issue

**Nerevar22g** · 12-10-2019,02:32 PM

Hello people, I have been recommended this forum for any technical help so here it goes.
I have a B6 S4 and in the last year I had a very annoying issue that nobody can figure out. Its a random hesitation at low rpm when engine is hot, runs fine when cold or if I rev up over 2500 rpm. What happens is when I press the accelerator, there is no power, car accelerates in a very uneven and jerky way until it reaches high rpm and then its fine. Usually if I feel that loss of power, I llift off the throttle, wait for a couple seconds, press the pedal again and its fine, pulls like a train. Its hit or miss. Also I noticed that RPM sticks to whatever range it was when I lift off the throttle or press on the clutch, then after 2 seconds rpm drops. Its so frustrating because its very noticable in city traffic. I have gunned the engine at full throttle up to 6000 rpm on a motorway and after that, it felt very responsive and powerful even at low rpm for a couple minutes, then it started happening again. I had diagnostics done several times, got nothing other than engine mount fault and abs sensor fault. Yes i got ESP and ABS lights on. I have replaced clutch and brake switches, spark plugs, decat, changed oil and all filters twice. Car runs beautifully when it works right. But nobody has solved this issue in a year now. Maybe some of you had similar thing and know how to fix it?
Thanks for reading

**jonathanfenton** · 12-10-2019,02:34 PM

Cam sensor?

**Nerevar22g** · 12-10-2019,04:08 PM

Thats a new one, wouldnt it show up on vcds as a fault code? How do I test it?

**jonathanfenton** · 12-10-2019,04:09 PM

Random hesitation and poor starting when hot could be a cam sensor. For the sake of £50 I’d pop one in especially on a car of that my age.

**Nerevar22g** · 12-10-2019,04:18 PM

as soon as I find where it is on the engine i will do it asap

**Crasher** · 13-10-2019,12:03 AM

What was/is the ABS code? If a sensor sends an incorrect signal to the ABS ECU this can lead to the engine ECU being instructed to reduce power whilst the ABS pump carries out individual caliper modulation in an effort to restore the cars driving line BUT this can happen when there is no problem, just because a wheel speed sensor ring is corroded and sending erroneous signals.

**Nerevar22g** · 13-10-2019,07:17 AM

the code is "00287 ABS wheel speed sensor rear right G44 30-00 - open or short to plus"
I was thinking that might be affecting the engine, but why only when hot and only on low rpm...

**Crasher** · 13-10-2019,12:00 PM

Firstly you need to get the sensor fault fixed as your car is unroadworthy at the moment. I think there will be more going on in the ABS than will actually generate a fault code, so the low speed wheel sensor readings need to be studied. For some stupid reason, the Bosch ECU cuts out and rips comms with the diagnostic system over approx 30kph but it is the values below this you are interested in.

**Nerevar22g** · 13-10-2019,09:45 PM

Unroadworthy

Its only abs
the engine problem happens regardless of the speed, could be driving in 1st or 6th gear as long as the rpm is under 2000, so I dont think its that. Even when stopped in neutral and reving i can feel the slugishness sometimes. Will see what happens after cam sensors are replaced, but will go back to the mechanic to check out the abs issue too

**Crasher** · 13-10-2019,10:32 PM

Originally Posted by Nerevar22g

Unroadworthy

Its only abs

With the ABS light on the car would fail the MOT under a major defect, do not drive notice... unroadworthy. If you had an accident where someone died, the ABS was found to be defective and was judged to have been able to prevent the accident, you would be up **** creek without the proverbial paddle. ABS has been deemed to have saved more lives than the three point seat belt...