lumpy idle, stumbling engine

[SwissCheeseHead]

Last week I started a thread about a lumpy idle, and ticking sound. Did the oil pumps bolts, which hadn't fallen out but were a bit loose, and the ticking went away but the lumpy idle is still present. During cruising, the engine stumbles and runs rough at 55mph, around 1800 rpms. Throughout the rest of the range, the engine runs lumpy, I guess is the best way to describe it. It feels very much like one of the cylinders isn't firing. I haven't pulled any of the plugs yet. Any thoughts as to what it might be? What is the best way to test?

The valve cover gaskets and plugs were replaced about 4 years ago. Since then, I've only put on about 25K miles. There is an exhaust leak, but I don't think it's related since the leak has been there for quite some time, at least a year.

[AHenry014]

Mind changing your details so your "My Cars" is accurate? I dont know what engine a three legged pony has.

Using context clues, valve cover gasketS was stated, so im assuming its an m60. Have you done the intake gaskets? I would always suggest to fix the known issues (exhaust leak) prior to moving onto anything else. How is the fuel pressure? I will say that the m60 is very sensitive to the MAF, and a bad MAF can lead to stumbling idle and running.

[SwissCheeseHead]

Changed. It's a 94 530i. I'm sure the exhaust leak is unrelated since it's been there for such a long time and this lumpy idle has only come up in the last week.

What's the best way to check the MAF? Should I disconnect it and see if it runs the same?

[AHenry014]

yes, I would start with disconnecting it and seeing if it runs any different. If it runs wildly different, aka stalls, then i would suspect it isnt the MAF. Have you done the intake gaskets? A large vac leak would have an effect like this.

[SwissCheeseHead]

You're talking about the intake manifold gaskets right? Is there a DIY somewhere. Is it a difficult job? I'll post results of disconnecting the MAF.

[SwissCheeseHead]

Stupid question. Is there a way to remove the security bolts holding the MAF in? I disconnected plug going into the MAF and there was little, if any change, but not sure if that was the same as physically take the MAF out of the intake hose.

[Tre0Tre34]

If you unplugged the MAF and there was no change, that is a good indicator that the MAF is either not operating correctly or the wiring is damaged.

Fully Removing the MAF itself is not part of this testing method.

Now to find a replacement (or a buddy who has a known good unit for further investigation)

[AHenry014]

If you unplugged the MAF and there was no change, that is a good indicator that the MAF is either not operating correctly or the wiring is damaged.

Fully Removing the MAF itself is not part of this testing method.

Now to find a replacement (or a buddy who has a known good unit for further investigation)

This.
The intake gaskets on the m60 are a commonly done maintenance item. Stumbling idle and general bad running can be caused by them. I recommend also doing the PCV plate, its gasket, and the throttle body gasket while you are in there. Also, stronly consider new knock sensors, as they are under the manifold and are likely extremely dry cracked and falling apart. Job is not difficult, just time consuming.
http://www.e38.org/intake/bmw740_intake.html

[SwissCheeseHead]

This.
The intake gaskets on the m60 are a commonly done maintenance item. Stumbling idle and general bad running can be caused by them. I recommend also doing the PCV plate, its gasket, and the throttle body gasket while you are in there. Also, stronly consider new knock sensors, as they are under the manifold and are likely extremely dry cracked and falling apart. Job is not difficult, just time consuming.
http://www.e38.org/intake/bmw740_intake.html

I did the PVC plate and gasket a couple years ago also. I don't know if I can source a MAF for testing purposes. If I were it get one, it would be replaced by a suitable, known working part. The wiring looked ok from what I could see, but I'll take a closer look. Thanks for the link to the intake gaskets. I'll try the MAF first.

[AHenry014]

I would certainly try with a known good working sensor. If that pans out, FWIW, I bought a brand new Bosch MAF sensor from BMA a couple years back for around 150. If you choose to buy from them, coupon code "bmwcca" is good for 5% off last i tried it.

[SwissCheeseHead]

I know it'll be frowned upon but I'm going to replace it with a cheaper aftermarket part. I'm kinda sorta planning on selling it once it starts running smoothly again. I just can't keep up with all the maintenance items that's needed. I don't have as much time as I use to.

[AHenry014]

Oh! just noticing this is a b30 car. They use the same exact MAF as a M50TU FYI.

[SwissCheeseHead]

Yes, it is a B30. Do you think cleaning the MAF will do anything? There wasn't too much of a change when I disconnected it but thought maybe a cleaning might be worth a shot.

[AHenry014]

cant hurt. I wouldnt bother with the expensive specific MAF cleaner for a potentially failing MAF. From my VW days, plastic bag with 91% isopropyl alcohol. Shake it in the bag to get the alcohol over the sensor. Do not touch the sensor with anything.

[SwissCheeseHead]

So just a gallon ziplock with 91% ISO and shake it up? I have both!

[AHenry014]

Yessir.

[SwissCheeseHead]

Cleaned with 91% ISO and that didn't help, so I ordered a new MAF. Should be arriving tomorrow.

[Sir Montalbon]

I just bit the bullet and got a new Bosch MAF to try on both my cars. So far I've only had it on the automatic sedan, but it made a very noticeable improvement in idle and all around smoothness of acceleration and shifts. And before that, I thought it was idling and shifting pretty good. Hope you get the same result.

[SwissCheeseHead]

I replaced the MAF about a week and a half ago. It does seem to have more pep, but the idle and lumpiness is still the same. It is most pronounced at 55mph cruising speed. I also noticed that my power steering pump squeals if parked for a couple days, until it can pump fluid through it. Wondering if these two things are related? A bad PS pump causing a lumpy idle? The PS pump does leak, and I have to refill it Pentosin every 6 months or so, but it's been leaking since I've had the car for 5 years.

[kouks]

Does the lumpiness appear to be sporadic or harmonic? If its sporadic, then it may be a general air leak, if it is harmonic (happens at the same time every time as the engine rotates), then its one of the cylinders.

For sporadic lumpiness: Have you checked the entire intake system for cracks or loose fitting hoses? The oil filler cap secure? VCG recent? Most likely an air leak in the system.

For harmonic lumpiness: Check each spark plug for condition, then go from there. If one of them is not like the others, you have your culprit. You may even have a bad or failing coil, which may not affect the condition of the plug, or create a very sooted plug due to inefficient burn.

Basically, this is a very general issue until you can start to describe the lumpiness in detail.

[SwissCheeseHead]

The lumpiness is definitely harmonic. It happens at normal intervals when idling and while driving. It is most pronounced at 55mph. Almost never fails to be "extra lumpy" at 55. At anything slower, it is bearable and doesn't feel like anything is going to explode. At 55, it is very much pronounced. I will check each of the plugs in the next coming days. Hopefully just a spark plug change to fix it...

Thanks for posting

[AHenry014]

how bout them intake gaskets

[SwissCheeseHead]

Not going to go there yet, but they could probably use a refresh. I'm not driving the car much these days so I'm probably going to sell in the next couple months. Just want it to run well before selling. If it's going to become too much of a time commitment from me, then I'll sell as is, but would rather not.

[SwissCheeseHead]

Still chasing this problem down. So far, I've replaced the MAF, replaced plugs, replaced the valve cover gaskets (there was oil in the spark plug wells), replaced one coil that looked blown out. The car runs smoother and the lumpiness is not as apparent, but it is still there and it still stumbles at 55 mph. Any other thoughts?

[Billyj]

Does it feel like power surges on the highway at partial throttle?