Low, rough idle - whats the cause?

[entscheidend 0]

Car is a 96 540i

When stationary and AC off, idle dips below 500RPM and appears to be rough with vibrations through the cabin. When you turn the AC on it jumps to 600/700RPM which seems ok but then after 60 seconds of remaining idle it drops again and seems rough with vibrations.

What I have done: Cleaned the ICV, Air temp sensor, MAF and checked for vacuum leaks.

I have disconnected the MAF, Air temp sensor and makes no difference. Driving her is no problem, she gets up and goes with no hesitation.

Could it be that she needs an update with the DME to increase the idle?

Or could the ICV be shot?

MAF?

Air temp sensor?

Cats plugged?

Ideas fellas??

[*Glenn* 854]

Get it scanned first....identicle problem here at work on a 740. CCV valve faulty & 1 ignition coil...all fixed now

[entscheidend 0]

Get it scanned first....identicle problem here at work on a 740. CCV valve faulty & 1 ignition coil...all fixed now

Had it scanned - no faults except for a continuous voltage from the DME???

[*Glenn* 854]

Had it scanned - no faults except for a continuous voltage from the DME???

Who scanned it ??

Maybe bring it over and let me take a look

[entscheidend 0]

Who scanned it ??

Maybe bring it over and let me take a look

ok - Ill pop in early afternoonish (1pm)

Thanks Glen

The intake gaskets have been done so I presume the CCV has been done. The PCV hasnt been done though

[*Glenn* 854]

ok - Ill pop in early afternoonish (1pm)

Thanks Glen

The intake gaskets have been done so I presume the CCV has been done. The PCV hasnt been done though

PCV & CCV the same

CCV= Crankcase ventilator valve

[entscheidend 0]

PCV & CCV the same

CCV= Crankcase ventilator valve

Woops I meant the oil separator

[*Glenn* 854]

About 1.00 is fine

[entscheidend 0]

About 1.00 is fine

Glen, I will swing around tomorrow morning. No time today with Month end crap at work ...

[*Glenn* 854]

Glen, I will swing around tomorrow morning. No time today with Month end crap at work ...

No problem.... were doing the same here Edited March 31, 2009 by *Glenn*

[BreakMyWindow 1870]

Just a question, it may not be related, but when u rev the engine from this low idle up to around 6 - 700 rpm and let the engine come back down to idle, does the engine stall, or almost stall? if so then its more than likely one or both of the cam position sensors.

Edited April 2, 2009 by BreakMyWindow

[*Glenn* 854]

Just a question, it may not be related, but when u rev the engine from this low idle up to around 6 - 700 rpm and let the engine come back down to idle, does the engine stall, or almost stall? if so then its more than likely one or both of the cam position sensors.

Checked it today...had a historical air mass sensor fault. Cleared fault codes, road tested, checked AMS readings....all ok and no more fault codes. Owner is fitting new plugs and we go from there

[entscheidend 0]

Glen, put new spark plugs in.

Has made a difference performance wise and has made it less "shakey" on idle. The problem is still there, just not as bad.

Could it be the thermostat? this hasnt been replaced at all. Or should I bring the revs up a bit? (sits at 400RPM with AC off)

Smoke test?

[entscheidend 0]

I am deciding on which to replace next - should I go PCV (Oil Valve ar rear of manifold... what ever it is called) of change the MAF??

[rjac001 0]

what about dizzy cap and rotor may have a crack or just need a clean?

[*Glenn* 854]

what about dizzy cap and rotor may have a crack or just need a clean?

This is an M60/M62 not a M20

Edited April 12, 2009 by *Glenn*

[*Glenn* 854]

I am deciding on which to replace next - should I go PCV (Oil Valve ar rear of manifold... what ever it is called) of change the MAF??

Need to have another look now that youve done the plugs... give me a call

[martyyn 2]

A friend of mine had identical symptoms with his 97 540i/6, I'll ask him tomorrow what the solution was and let you know.

rjac001, you seriously need to take a step back and ask yourself if what your posting is relevant. At the moment most of it is just rubbish. Two people with 540's have similar issues and the only thing you have to say is to check the dizzy cap

[BM WORLD 1264]

what about dizzy cap and rotor may have a crack or just need a clean?

thanks for that can you tell me where the dizzy cap is ???

[Jamez 2147483647]

right next to the sidedraft carburetors

[rjac001 0]

Ok ok just trying to help Should have read the original post..

Maybe this Will help then:

M62 Misfire faults

Model:

E31 – 840iA produced from November 1995 to October 1996

E38 – 740i/iLA produced from December 1995 to October 1996

E39 – 540i/iA produced from March 1996 to October 1996

Complaint:

The check engine lamp is illuminated, and fault codes 50, 51, 52, 53, 54, 55, 56, 57 are set in the DME. The misfire faults may be caused by low or no fuel, poor fuel quality, high or low fuel pressure, ignition coil, faulty spark plugs, restricted or contaminated fuel injectors, crankshaft position sensor, poor combustion through low compression or high leakage, or a blocked or restricted catalyst.

Remedy:

Check the above possible causes for misfire, and rectify if necessary, then clear all faults. Or reprogram the DME using MODIC programming software P9.0 or higher. If the vehicle was produced between December 1995 and September 1996 the reprogramming is a necessity.

When testing the new software test the vehicle with the same conditions the misfire first occurred at. If the misfire continues then check the secondary voltage pattern, ensure there is no damage to the catalyst, check the above possible causes, then reprogram the DME.

[entscheidend 0]

It has to be the PCV Valve all clogged up, maybe the spring is stuck in it?? It doesnt have much in the Bentley Manual about this

Glen - Will try to find some time to come out your way

Martyn - Be good what you find out about that 97 model

Rjac001 - Dizzy Cap?? on a M62 the centre caps make you "dizzy" while the car is in motion if you stare at them; I checked all 4 and they were all good.

[entscheidend 0]

Glen - finally got time to do my PCV/CCV this weekend and I found my torque wrench.

I am changing the Oil tube (from block to diaphram), intake gaskets x 4, vent tube o rings (inside CCV), rear cover, gaskets both ends.

Will post Sunday to see if there was a difference

[darkwolf 0]

My 1998 540i is currently in getting an intake valve replaced. Failure sucks big time. You haven't noticed any oil out the exhaust or squealing from the engine when it happens?

[entscheidend 0]

My 1998 540i is currently in getting an intake valve replaced. Failure sucks big time. You haven't noticed any oil out the exhaust or squealing from the engine when it happens?

Na - no smoke, oil anything. When the car is cold you can hear the manifold whistle when you gun it - and is quite jerky under 1500RPM