1995 540i, Rough running at Idle????

[balboaislandbob]

Hi all, we just bought a 1995 540i at auction with 105,000 miles on it. My better half Sophia loves the car. It runs rough at idle (shows 750 +/- RPM). We put new spark plugs in, it passed the smog check real clean, and the compression checked out fine. Yet, it still runs rough at idle. Any thoughts out there?

[JPower]

Hi all, we just bought a 1995 540i at auction with 105,000 miles on it. My better half Sophia loves the car. It runs rough at idle (shows 750 +/- RPM). We put new spark plugs in, it passed the smog check real clean, and the compression checked out fine. Yet, it still runs rough at idle. Any thoughts out there?
:cry: most likely the engine is bad , you need to do a leak down test on the engine .
BMW V8 engines between 1993 and 1995 devolped this problem because the sulfer content in the fuel was damaging the cylinder wall coating.
Do not install a used engine most likely it will be the same, you need to buy the block from the dealer, the new blocks have been improved from BMW. Good luck

[Bob in San Jose]

The first thing to check is if the block is Alusil or Nikasil. Go to koalasport.com, there is a good writeup there on this problem and how to check the engine block casting number to determine the block type. Even if the block is Nikasil, "The Bad Block", there is a good chance it is OK.
The problems with these engines occurred after 30K miles not 100K.
The more likely problems for erratic idle are vacuum leaks. At 100K the intake gaskets, vacuum hoses, and EGR device at the back of the engine have probably developed leaks.
I have a 95 540iA with the Alusil block, replaced the Nikasil block at 39K, that was exhibiting the same problem and I had the above gaskets and hoses replaced to fix it.
A leak down test is a good thing to do if the block is Nikasil but I would check/do the gaskets/hoses if they have never been done.

Bob
1995 540iA

[Qamar]

Hi

I have 1995 model, V-8 automatic. I had the similar problem. I had changed the 02 Sensor. Now the car is perfect. Before you change the 02 sensor pl get it checked weather it is working or not. If you know the procedure of checking it is good, otherwise let me know, i will write it back to you.

Qamar

[LozinOz]

My 540i had a rough idle on cold starts when I bought it. Not severe at first but got worse over 12 mths. An open front door would shake severely for a minute or more after startup and then it would smooth out quite quickly, but still miss quite a bit. I was confident from BMW dealer leakdown test/compression test etc that the engine was in very good order.

Early on I replaced the cover/oil separator at back of intake manifold (without taking the manifold off) on advice from BMW that it was a common point of failure. This didn't fix the problem.

More recently, when it got too severe to leave, I replaced the intake manifold gaskets, front cover gasket, a couple of rubber seals, and had the injectors cleaned. Two injectors were slightly down on delivery and one was down 40% before they were cleaned. About a day's work all-up.

Result was outstanding - engine just purrs and idle is brilliant hot and cold. Fuel consumption went from 13.5 l/100km on a trip to 9.6.

[ThoreauHD]

02 sensor. Intake manifold gasket. Valve cover gasket. Air filter. Oil filter. 0w-40 Mobil 1 oil. Injector clean. Later- Transmission fluid/filter/seal.

Do a idle check at a BMW service center. They'll spot it quick. I bet the thing has a bit of erratic acceleration/shifting too yes? Pretty much all your rubber parts go to hell at that mileage. Don't go to a dealer for this, but a BMW independent service center. 60 and hour vs 100 an hour makes a big difference, since it'll be all labor. The parts don't cost anything.

[junoon0977]

I have a 1993 525i that idled rough. Mechanic found an air leak underneath the intake manifold due to a missing O ring on the pipe that runs from Idle Valve Controller to the intake manifold. Air leaks are usually the most common reason for rough or irregular idling.