E85 Z4 Rough idle

W

WillB11

Member
Hi guys,
I bought a 2007 2.0l Z4 about a month ago. The guy I bought it from didn’t seem at all dishonest, but within a week or two it was in the garage for a couple of things; Valve actuator motor change, rocker cover gasket change for an oil leak, and also got the oil and filter changed for good measure ;).

The car ran amazingly straight out of the garage, pulled better than before and I didn’t notice anything odd during idle.

Yesterday however, I noticed at some traffic lights some mild shaking in the car and the gearstick was vibrating a lot more than I remember. I have read and seen that the 2.0ls are notorious for having “lumpy” idles, but it just seems odd as i don’t recall mine being particularly bad before taking it in to the garage.

It almost felt like a very small possibly intermittent misfire, so I plugged in my code reader and had a look. The revs were bouncing between 790-815rpm (seems low to me but not sure) . Code 29F4 also came up even though an engine light wasn’t on, relating to the cat efficiency.

Since then I have changed the air filter, cleaned the MAF sensor and checked for any obvious cracks in intake hoses, nothing.

The car drives pretty smoothly at higher revs but when you put your foot down it can sometimes hesitate.

Is it possible that this could be a spark plug issue where at low revs it is not working properly?

Any advice would be much appreciated because as you can tell I am pretty stumped and it could be a whole load of things. Also, pictures will be following up on this post when the weather decides to sort itself out :wink: .
Cheers!
 
Might be worth adding - the car has 101000 miles on the clock and the spark plugs were last changed at about 75k. From what I can see coil packs haven’t been changed, however I have experienced the misfire when a coil pack goes and it is no where near as bad as that!
 
Coil packs can fail to different degrees, sometimes the insulation breaks down inside them intermittently so i wouldn't rule them out. More likely though is oil contamination on the eccentric shaft sensor (remove the electrical connection and look is connector is wet). The cat efficiency thing is very very common on the 2.0l unfortunately and seem hard to resolve. They can sometimes be associated with cracked exhaust manifolds which again most 2.0l suffer from at some point in their lives.
 
I personally doubt it is the spark plugs.
I swapped mine out, hoping it would smooth out the idle, but it made no difference.
The car did run notably better but I suspect the ones I removed were original at 100k so that's not surprising.

Still a cheap shot in the dark at only 20 quid so maybe worth a go.

Replacing both mixture control 02 sensors actually did help a bit. My car only idles rough in open loop when hot so a sensor fault would make sense. Problem still not cured completely though.

My next items to check will be the exhaust manifold (for cracking at the welds) and the timing chain, guides and tensioner for wear or breakage.
I have already tried disabling the valvetronic system and saw no change so I am assuming the problem doesn't lie there.

Best of luck finding the cause. These engines do like to throw their toys out the pram every now and then.
If you get to the bottom of it, please let us know! It does bother me sometimes.
 
Cheers for the replies guys,

Coil packs i will have to look further into then and i agree spark plugs are cheap enough so I may as well swap them out to be sure.

I will look into the oil contamination on the eccentric shaft and see what comes of it! Also o2 sensors could be a cause but I saw on my code reader that the voltages coming from them meant they aren’t completely dead but whether or not that means they are working properly is another thing.

I called up the garage that did the valvetronic work and they said they’re happy to have a look into it for me tomorrow morning. He seems to think it could be a coil pack too although when I say “rough idle” it is pretty subtle. You can definitely hear something going on while the engine is idle - as I said its almost as if it’s about to misfire but then saves itself ...
 
I don't know about the 2.0i, but I have had loads of N52s over the years in various models.

One thing I have found that when you replace anything like disa valves, sort out vacuum leaks, replace injectors etc. etc. the car often needs all adaptions reset.
If you have had a sticking valve the car will do its best to adapt to keep it running as smooth and as close to spec. Suddenly swap out a failing part with a new one and the car needs to know to lose those adaptions it has done.

I would ask them to do an adaption reset and see how it goes.

I warn you now, when it resets and you restart the engine the idle tends to be all over the place as it tries to sort itself out. Restart it a couple of times and it should sort itself out, the engine management light will probably come on, but that will go out after 3 drives of 5 miles or so.

You may find that sorts it for you. :thumbsup:
 
gIzzE said:
I would ask them to do an adaption reset and see how it goes.
Click to expand...

Thanks, I have read that some people with 2.0ls ask their garage to reset the throttle mapping or something... I’m guessing this is something similar. I will mention this to them tomorrow if they don’t find anything obvious :thumbsup:
 
If it has not been set up, you can try the following to reset the valvetronic motor start/stop points.

Switch the ignition onto position 2 and within 15 seconds, press the accelerator pedal down to full throttle and off again 10 times and you should hear the valvetronic motor program itself back to factory spec.
 
Sorry I haven’t given an update! So, i’ve had the car back from the garage about a week ago and have been driving since!

So, the car had a knackered O ring near the rocker cover gasket (I think that’s what they said) that was leaking oil into one of the spark plugs, causing an intermittent misfire. They replaced the O ring and cleaned the spark plugs, and since then the car doesn’t hesitate at all which is awesome!

The car still idles a bit rough but as it is a common feat of the 2.0l’s i’ve sort of come to terms with it, however I will still be looking into it. Possibly I will look into a throttle reset map or o2 sensors...

Cheers for all the advice guys! Bloody 2.0l’s !!! :headbang:
 
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