HELP! "91" M5 QUESTION.

[highlander m5]

Hi, I`m New To This Forum, And Was Hoping Someone Could Help Me With This Problem.
I Have A 91 M5 3.6 With 118,000 Mls On The Clock. The Service Record Shows That It Had A New Engine Fitted At 60,000 Mls.(i`ve Had This Confirmed By The Dealer Who Carried Out The Work.) The Problem Is That It Runs Rough When Idling And Cruising. It Doesn`t Cough,missfire Or Want To Cut Out, It Just Sounds Lumpy.as Soon As You Let The Clutch Out And Start To Move Or Sit Still And Rev The Engine Its Fine.
Its Starting And Switching Off Ok.i Put It Into My Local Bmw Garage And Thay Checked The Valve Clearences, Injectors,exhaust Emissions,engine Management System Codes, All Ok. The Hoses From The Inlet Manifold To The Engine Were Checked And Some Replaced But Made No Difference.
It Was Also Suggested That When You Take The Oil Filler Cap Off With Engine Running That It Should Stop. Is This True Because I Tried That An Mine Doesn't Stop?
I Would Appreciate Any Suggestions On This Matter As I Don't Want A Small Problem To Turn Into A Big One!
Cheers

[mike wong]

have you done a service II inspection? check all the "normal" stuff: fuel pump, fuel filter, O2 sensor, distributor cap, rotor, spark plugs, wires, etc.
Since you mention the oil cap removal test, you should ckeck all your vacuum hoses, as one may be leaking...

also change your water pump if it hasn't been changed in 60K.

a great place for parts is BMA.

[highlander m5]

Thanks For The Info Mike .
The Water Pump And The Radiator Look New.
I`ll Book It In For A Service Ii Inspection And See What Happens.

Cheers.

[highlander m5]

Thanks For The Info Mike .
The Water Pump And The Radiator Look New.
I`ll Book It In For A Service II Inspection And See What Happens.

Cheers.

[MotoMan]

Hey there Highlander. U mentioned that your vehicle shows no change when you remove the oil filler cap. It is supposed to at least run as though it were missfiring. This is because the eng sucks air from the filler and the dme cannot understand the additional air. I would assume from what you say that there may be an air "sucktion" problem. IE your eng is sucking air that is not being measured. Mabe an airmass failure ???

[632 Regal]

not "stop" there should be a noticable change as soon as you take the oil cap off compared to with it on. If there is NO change than it's usually a vacumm leak.

[highlander m5]

Had Service Ii Inspection Done.all Ok. Vacuum Test Was Done On Inlet Manifold And Showed No Fault. Hoses Checked Ok.
It Was Mentioned That It Could Be Something To Do With The Auxilliary Air Pump.does Anybody Have Any Info On This ?

Thanks For The Replys So Far.

[632 Regal]

yes that could be messed up and either not letting in enough bypass air or sticking and letting in too much air.

[mike wong]

let's make sure we are describing the same part. the aux air pump that is near the alternator normally only runs for about 10-15 minutes when the engine is "cold". It makes noticable noise when running. After the enigne and CAT are at normal op temp, the pump is turned off. So there should be no effect after 15 minutes of driving.

Is the engine running rough a new problem, or has it always been occuring; as the 'normal' idle for the M5 has never been 'smooth' (due to the cam timing).