Fluctuating Idle

[brad.210]

Hello all

I have a Z4 3.0si e86 (N52) approx 52k on the clock, and it appears to have developed a consistent fault whereby when I start the car regardless of the engine being from cold start or at normal tempreture the idle fluctuates between (estimate 650-900) and then after setting off settles down.

This morning was particularly colder (1-2'c) and the fault persisted after setting off (although it drove normally and appeared to disappear and return to the above behaviour after the engine had reached operating temperature)

I plugged in my ODB and it had a pending fault p0017, although it didn't throw it and it went on its own after restarting the engine. So I don't think that's related

The MAF sensor has been changed already.

Does anyone have an ideas?

 

[firebobby]

Have a read up about the Vanos valve, I think these can make the engine idle a bit weird

 

[Toe-side]

Could be MAF, coil packs, Vanos.
Any fault codes?

 

[brad.210]

No fault codes being thrown.

Only that p0017 which was pending but then wasn't thrown on the next engine restart. So I discounted that in regards to this issue.

Replaced MAF already.

Could a bad coil cause this kind of problem, wouldn't it just mis-fire completely?

Don't have any knowledge over Vanos, will look into it.

 

[Talksthetorque]

Google tells us that P0017 is exhaust side crank position sensor.
www.bimmerfest.com/forums/showthread.php?t=514883
Apologies for link to other site.

 

[brad.210]

Thanks for link, the problem I'm describing has been happening for weeks, I haven't had any permanent codes stored.

Could that sensor being faulty (in a transient sense) potentially cause the fluttery idle or would you edge your money on coil packs/something else?

Don't suppose you know the part number for that potentially problematic sensor?

 

[ba3bas]

Hello mate, unplug your maf and see if the issue happens when you start the car.

It probably wont

Get your maf swapped out and should be fine.
Check the intake has no air leaks if you have fiddled with anything as that causes the same issue.

Basically the car seems to be hunting for the correct air/fuel mixture and then balances out.

Last thing to swap are the primary lambda probes in the exhaust manifolds.

 

[brad.210]

Ok thanks, I'll try unplugging it. I've actually had that replaced (or so I thought), so hadn't expected it to be that.

 

[Smartbear]

Our mini was recently exhibiting the same symptoms & was cured by purging the vanos solonoids.
Regards

 

[Toe-side]

If MAF has been changed and no codes (apart from those discussed) then Vanos solenoids

 

[ba3bas]

Our mini was recently exhibiting the same symptoms & was cured by purging the vanos solonoids.
Regards

How do you do that then?

 

[GreyZed]

I had an erratic idle a while ago. Seemed to drop a cylinder every few seconds on tickover but no probs on the move. Turned out to be a coil pack.

 

[Wildfire]

Our mini was recently exhibiting the same symptoms & was cured by purging the vanos solonoids.
Regards

How do you do that then?

I had that code it hasn't resurfaced since I cleaned the VANOS solenoids. It's pretty easy. They are right on the front of the engine opposite the rad/AC condenser. You just need to unplug them, then one at a time, unscrew the retaining bolt. Take each one out, give it a good clean and reinstall.

 

[Roundozo]

Tempted to do this to mine just for good measure. What did you clean the solenoids with and did you replace any of the O rings?

 

[brad.210]

Interestingly got the engine to temperature, And unplugged the MAF, it noticeably runs higher idle revs, and doesn't appear to be fluctuating.

Plugged it back in, fluctuating again.

Beginning to wonder if this is a new MAF after all? Or could it be that when I take out the sensor it is potentially hiding the real issue?

 

[Roundozo]

Is it a genuine MAF. What I mean by that is that I know my old E46 would suffer if aftermarket sensors were put in. I know that BMW's can be temperamental with non oem electronics.

 

[brad.210]

Funny you say that because just been out thier thinking the same, and its made by continental.

Im sure thats incorrect for this model?

It reads on the face of it.
Continental
5WK97502Z
PBT-GF30
050073384
0001148

 

[Wildfire]

Tempted to do this to mine just for good measure. What did you clean the solenoids with and did you replace any of the O rings?

I used petrol and some compressed air. I took the o-rings off first. they were still sealing well and wee soft so I just reused them.

 

[Wildfire]

Tempted to do this to mine just for good measure. What did you clean the solenoids with and did you replace any of the O rings?

I used petrol and some compressed air. I took the o-rings off first. they were still sealing well and were soft so I just reused them.

 

[Smartbear]

Our mini was recently exhibiting the same symptoms & was cured by purging the vanos solonoids.
Regards

How do you do that then?

It's done via the obd port & the diagnostic kit, the idle speed is increased for a couple of minutes & I think the solonoids are both switched on to purge the system-it seems similar to bleeding.
Idle was rock steady after this procedure.
Regards