BMW M50 Idle Shake Help!!!

[edgemar]

Pelican Braintrust:

This has been driving me crazy and I've not found a solution after weeks of searching all the BMW forums. Please help!!! it's a 93 325i bmw.

I've spent a bunch of money to catch up with all the deferred maintenance on this car and it drive greats except the engine shakes at idle. It has a rock steady idle but you can see the engine shaking in the engine bay and the car vibrates. It hasn't always done this...only in the past month or two. It idles at about 550 rpm...

I'm thinking now that the car has a low idle for some reason...any additional rpms and the engine seems to smooth out. The engine performs fine while driving along.


Here is what I've done so far to try and fix the issue:

1. checked each coil for operation
2. checked resistance at each coil per bentley with multimeter
3. checked visually for vacuum leaks.
4. replaced fuel filter in june.
5. replaced spark plugs with NGK BKR6EK
6. Running premium chevron gas and put techron last fillup.
7. unplugged map sensor to see if there was any change. = no change
8. replaced motor mounts
9. replaced fan clutch
10. bled coolant system
11. clean air filter installed
12. no arcing of ignition components observed
13. no or very little oil in the spark plug holes.
14. replaced all coils.
15. cleaned idle control valve.
16. no codes it's OBDI

- replaced the vanos a few months back with dr. vanos rebuilt unit.

Any thoughts would be greatly appreciated!!! This thing is driving me crazy. I bought some new Bosch plugs but i don't think it will make a difference.

I'm also willing to take it to an expert. If anyone knows someone that's really good with old BMW's please chime in!

Thanks so much for your help!!!

[Scott Douglas]

Just as a point of interest, my old '85 325e wouldn't run on platinum plugs at all. Put in silver tips and it ran fine.

[widebody911]

You can still pull codes on an OBDI car. Find a friend with Peake RC5 reader.

[Heel n Toe]

I would recheck everything about the motor mounts replacement. Depending on the placement of the transmission mount/s, maybe that/those, too.

[Jim Richards]

edgemar, I think your idle speed is too low. This web page says the idle speed should be 800 ± 30/min. M50 Engine (E36) - BMW 3 Series

Have you checked the engine timing? The dizzy might be off.

[Rick V]

Are you missing a blade on the fan?

[nikita76]

I had similar problems and changed a lot of similar items that you have. Changed the O2 sensor and all is well. $76.00.....how does such a small part have such a huge impact?

Good luck!

[edgemar]

Originally Posted by Jim Richards

edgemar, I think your idle speed is too low. This web page says the idle speed should be 800 ± 30/min. M50 Engine (E36) - BMW 3 Series

Have you checked the engine timing? The dizzy might be off.

The engine has coil on plugs so i'm not sure how to adjust timing...is it in the dme? Thanks for the link to that site!

Originally Posted by Rick V

Are you missing a blade on the fan?

Fan Blade is good. Checked it carefully when i did the fan clutch a few weeks ago.

Originally Posted by Heel n Toe

I would recheck everything about the motor mounts replacement. *Depending on the placement of the transmission mount/s, maybe that/those, too.

It acts the same with the new motor mounts as before

Originally Posted by nikita76

I had similar problems and changed a lot of similar items that you have. Changed the O2 sensor and all is well. $76.00.....how does such a small part have such a huge impact?

Good luck!

did a a bad 02 sensor throw a code?

Something is causing this low idle....

[Jim Richards]

Check timing first to see if it's right. If so, it's another thing to eliminate.

[fastfredracing]

The pvc systems in these cars go wonky, and makes what is basically a large vacum leak that is not to atmosphere ,but into the crankcase. You should have a slight, vacum at the oil cap when you take it off. If there is a really strong vacum present here, that sucks your hand down on it, a faulty pcv valve is your likely culprit.
Is it running smooth on all 6 holes, or is it a missfire? Have you tried to kill one cylinder at a time to see if this is a problem isolated to one cylinder, or the whole motor.
These are the first few things I would be looking at if it rolled in here.

[asphaltgambler]

Originally Posted by fastfredracing

The pvc systems in these cars go wonky, and makes what is basically a large vacum leak that is not to atmosphere ,but into the crankcase. You should have a slight, vacum at the oil cap when you take it off. If there is a really strong vacum present here, that sucks your hand down on it, a faulty pcv valve is your likely culprit.
Is it running smooth on all 6 holes, or is it a missfire? Have you tried to kill one cylinder at a time to see if this is a problem isolated to one cylinder, or the whole motor.
These are the first few things I would be looking at if it rolled in here.

Exactly where I was going........................

[Tim Hancock]

Dirty/malfunctioning idle control valve or cracked hose/vacuum leak is my "guess".

[edgemar]

Originally Posted by fastfredracing

The pvc systems in these cars go wonky, and makes what is basically a large vacum leak that is not to atmosphere ,but into the crankcase. You should have a slight, vacum at the oil cap when you take it off. If there is a really strong vacum present here, that sucks your hand down on it, a faulty pcv valve is your likely culprit.
Is it running smooth on all 6 holes, or is it a missfire? Have you tried to kill one cylinder at a time to see if this is a problem isolated to one cylinder, or the whole motor.
These are the first few things I would be looking at if it rolled in here.

I pulled the oil cap and there is a slight vacuum and you can hear the engine sound just a bit different...no real sucking going on though.

I pulled each coil while the car is running and there is no change from one to the other.

I also cleaned the ICV valve last weekend with no difference.

[Scott Douglas]

After re-reading your first post, did replacing the vanos unit involve the throttle linkage at all?
If so, I'd guess you just need to make an adjustment to the stop so it idles a tad higher. 550 is pretty low.

[Flat Six]

*** My best guess is PCV ***

However, no substitute for good diagnostics. Is your CEL operating properly? If so, these are the 2 must-do diagnostic steps for your situation, IMHO:

1) Check for trouble codes. Borrow or buy a Peake reader, or count flash codes (one explanation of the process is here: BMW Diagnostic Flash Codes: Bimmerzone.com)

2) Check vacuum readings. Use a gauge, don't just visually check for apparent leaks. Diagnosing via vacuum gauge is a wholly underappreciated skill. Shame, because it's simple, cheap, and very informative.

Good luck.

P.S. Quick question -- does this happen w/engine warm, cold, or both?

[edgemar]

Originally Posted by Flat Six

*** My best guess is PCV ***

However, no substitute for good diagnostics. Is your CEL operating properly? If so, these are the 2 must-do diagnostic steps for your situation, IMHO:

1) Check for trouble codes. Borrow or buy a Peake reader, or count flash codes (one explanation of the process is here: BMW Diagnostic Flash Codes: Bimmerzone.com)

2) Check vacuum readings. Use a gauge, don't just visually check for apparent leaks. Diagnosing via vacuum gauge is a wholly underappreciated skill. Shame, because it's simple, cheap, and very informative.

Good luck.

P.S. Quick question -- does this happen w/engine warm, cold, or both?

1) no trouble codes when using the flash method.

2) do not have a vac gauge.

it seems to shake most of the time. maybe no so much when cold.

[Flat Six]

Originally Posted by edgemar

2) do not have a vac gauge.

$15 at your local FLAPs.

If problem persists whether cold or hot, then nothing to do w/O2 sensor (open v. closed loop).

Still sounds vacuum/ventilation-related. Scott also points out additional source -- throttle body/linkage. Is there a separate idle switch on the M50 or is it part of the TPS?

[Nostril Cheese]

I also think this is a PCV related vacuum leak. Ran into this on a car a while back.

[dewolf]

Get some maf cleaner and spray around the throttle body and associatted hoses etc. If your idle speed changes something is amiss. Wifes 540 did this and turned out to be a leaky throttle body gasket. When I removed it, it literally fell apart.

[onewhippedpuppy]

You said unplugged MAP sensor on #7, but do you mean the MAF sensor after the air filter and prior to the throttle body? If you removed the connector and nothing changed then the MAF is probably bad.