E39 540 - low idle & poor gear change when hot

[yrshaik]

Greetings.

I have noticed the following on my late 98 540 auto. The gear down change when comming to a stop is jerky, when the car is hot - having been driven at least 50km. I have posted a question regarding this in a previous thread and following advice had the gear box serviced - no difference.

However, I now notice that the idle is also quite low, a little under the line, when the car is hot. Switching on the aircon raises the idle and the poor downshift problem disappears! This low idle only occurrs after driving for at least 50km. The engine reaches normal temp from cold within the first few Km, so I wonder what could influence the idle. I have also replaced the MAF with no change. HELP!

[darkhorse737]

when was last change of air filter? what other service history have you for the car? Last tune up? Current mileage?

If you have access to a scanner, maybe you can obtain the values, and I can decipher for you what could be wrong.

If none, dirty throttle body, ICV, TPS, and possible vacuum leak will be the next possible causes.

[marti5]

Most of the V8’s suffer from this at some time or other and the symptoms are very similar to Nikasil wear in that the car rocks at tick-over. There often is a pronounced lack of power that can be intermittent, getting worse in damp conditions. It differs from Nikasil wear in that the power loss is evident at all revs whereas Nikasil has a pronounced lack of power at low revs and is less significant at higher revs. This fault and a split PCV valve (aka bellows) are quite simple faults to fix on the V8 and you can often pick up a rocking V8 for next to nothing because it is perceived as Nikasil wear.


Oil down the sparkplug holes on V8's is quite common, just a small leak from the rocker cover bolts or gaskets and the oil has no-where to go except for around the plugs. Although oil is an insulator, it damages the stub HT leads eventually causing the rubber to disintegrate and allowing the spark to travel through the rubber and straight to the head. Before the complete failure of the rubber it becomes loose on the sparkplug and sparks can travel down the side of the insulator. With the high compression ratio (10:1) on the V8 the spark likes to go anywhere except across the electrodes of the plug!

The oil tends to accumulate on the rear pair of cylinders initially due to the backwards cant of the engine but after a while they will all get filled up and certain gasket failures will fill up odd plugs rather than travel all the way to the rear cylinders.

Repair can be as simple as clearing the oil from the apertures and fitting 'O' rings to the stub HT leads that have been damaged. Where the stub HT leads are disintegrating they can be replaced as separate items from BMW for around $5 per coil, there is no need to replace the whole assembly

As for the jerky change on your box, I would get the fluid level checked as some box service technicians dont fill it correctly, here is the correct procedure, please take attention regarding the Air-con must be on at the last fill:

How to:

> car up minimum 400mm, must be dead level.

> Start up.. 10mins turn off

> remove bottom plug and drain fluid / BEWARE HOT FLUID BURNS !! / safety goggles required

> replace pan plug

> remove all pan screws / clips that hold wires to the pan/ be careful there will be fluid still in the pan!!

> remove the 2 filter screws / there will be fluid left in the filter !!

> clean out pan and the four magnets/ lint free cloth / degreaser or brake cleaner

> clean surfaces for gasket

> screw in new filter / make sure its in flat and take care to get the 'O' ring in correct

> replace the four magnets

> place gasket on pan with a little fluid / replace pan

> Undo fill plug / drivers side rear

> start filling until fluid dribbles out / replace plug finger tight

> start car... go through all gear selections slowly 3 times keeping foot on brake / then in 'P' turn off after 10 mins

> undo filler plug fill some more until dribble comes out / plug back in finger tight

> Start car put in 'N' ....now be careful not to burn yourself!! whilst car running (Air-con on full blast) undo filler plug put more fluid in until it dribbles out again, put filler plug in and tighten.

[yrshaik]

Thanks for the response guys.

The idle problem seems to be just that. Low idle. The engine still runs smooth and no noticeable loss of power.

I replaced the MAF and air filter myself a few weeks back. Also took the motorised throttle body out and cleaned it out. I checked the rubbers/seals/gaskets from the air filter to the engine ie. the complete air path. All ok.

Spark plugs and oil was replaced about two months back. I did find traces of oil on one spark plug, but nothing significant.

As for the gearbox, I was present when the oil was filled, and it was done in the described manner.

Any other ideas?

[darkhorse737]

that leaves TPS calibration or possible intake manifold leak...