Weird idle

[Jonny3777]

Hi all,

Hoping for some help with an ongoing issue. My 2006 2.0 Z4 has been having idling issues, when sitting stationary the needle will hover between 600 - 1000 revs up and down. Its very random, I have two fault codes

Threshold efficiency low cat bank 1

Secondary air injection system insufficient flow bank 1

Im guessing these are linked, it was the cat bank 1 code for a long time then the secondary air which I've noticed only recently. Possible air leak, air pump or valve issue.

Also when driving at 100kph/60mph my revs in 6th gear are about 2,100 - 2,200 and driving at 120kpm/70mph I'm at 3,000 revs, is this normal?

She's burning oil also and I'm not sure why. Some said it maybe the valve stems, others said the O2 sensor but I don't know.

Its driving me mad I've been to 2 different garages to find out but no answer as of yet.

Anyone have any ideas?

 

[colb]

Need to have a look at what the exhaust sensors are doing in live data and a look at the fuel trims, bad idle could be down to air leaks in the vacuum system across the engine, check for split or holed rubber vacuum pipes. If you can’t find any leaks a smoke test will find them. If it is down to unmetered air that hasn’t been measured by the Maf the exhaust sensors will see it and think the car is running lean, it will increase fuel at the injectors to riches the mixture hence a look at the fuel trims in live data with diagnostics plugged in is a good check. When viewing the exhaust sensors the pre cat sensors should be cycling up and down their voltage range in graph form you should see a rising and falling trace line if they are performing. A good clean of the idle control valve and throttle body would also be worthwhile doing.