E34 ///M5 wetness.

[1st 5er]

Wednesday, late morning, in the rain, I left the house in the E34 ///M5.
I noticed a bit of rough idle after the noisy air pump thingy quieted down.
During the 3 miles I drove it, it stumbled a bit at a couple of stop lights and signs.
Actually at every low RPM point it stumble (idled poorly), and then finally died in the middle of a major intersection.
I was able to restart it and get enough forward motion going to coast into a gas station about a block away.
I pulled in, filled the tank, tried restarting without significant success.
It did finally start a couple of brief times but would not rev.
Pushed it up to the store's front and got a wrecker to drag it back to the house.
Just went outside, after it sitting there drying out today and it fired right up.

WTH?

Any ideas as to where moisture could have gotten, what got wet, with it just sitting there in the driveway in the rain?
Of course the hood was closed!
We've had a couple of rain days since 11/11/11, the day of purchase,
but between Tuesday evening and late Wednesday morning we had nearly 4 inches of the liquid stuff.

Thoughts anyone?

[mooseheadm5]

Start it and hose down the motor with low pressure water (methodically.) I'd go for the crank sensor first, but it could also be a bad ignition system component or even O2 sensor since they can be sensitive to humidity/wetness.

[1st 5er]

Excellent.
I'll get out the spray bottle I use to check for air leaks in tires, and replace the dish soap water mixture with fresh water.

Thanks.

[skip535i]

Another vote for wet o2 sensor. I say get the car on jack stands and check out the wiring underneath. I think you'll find the issue quickly.

[ahab]

Doesn't the E34 ECU live in the engine bay? Might check the seal around its little enclave. Check your spark plugs wires closely too. I had those same symptoms and it was a cracked resistor in the #6 plug connector. It was cracked inside the boot and rather difficult to diagnose. In wet weather it would wreak havoc on the ECU because it would ground out and the ECU wouldn't get the correct position info over that piggyback wire to the DME harness. I replaced the resistor and the problem went away. Mine was accompanied by a lot of backfiring too, so your problem sounds a little different but I wanted to pass it on as it may be relevant.

Edit: There's also this from another post, I don't think it was E34 however.

"I'm glad you guys figured your problems out.
Mine was a hole in the bottom of the fuel tank vapor recovery box. When it rained it sucked a little water, and sent it to the intake manifold. Hit a puddle, pull over quick, engine died, wait ten minutes, try it again.
Since I live by LAX this was an infrequent problem so I sometimes forgot about it. I noticed the hole during a brake pad replacement, and duct taped it. HA! No more puddle problems! I replaced it with a junkyard box, and no more issues since." - gidgaf

[MicahO]

You've got great stuff to work on from the pros, so I'll just say I'm glad you are getting some rain, and I hope that at least some of it is soaking in.

GLW the diagnosis and repair!

[djazz]

Fixed yet? I vote for O2 sensors also. Is the answer in another thread?

[tn535i]

Condensation//wetness in the distributor cap will do funny stuff as engine temp changes. Might be worth having a peek.

[1st 5er]

Fixed yet? I vote for O2 sensors also. Is the answer in another thread?

No, haven't messed with it since I started (you'll have to guess what).

Since deciding on the E12 conversion it's pretty much just been parked.
I kinda figured I'd freshen everything up at that time and hopefully the situation won't carry over.

[tschultz]

Now maybe it will run properly because it's jealous of the other!

[1st 5er]

[djazz]

Now maybe it will run properly because it's jealous of the other!

Amazing how that works sometimes. It can backfire if she gets too jealous though.

[1st 5er]

I think I found the problem...

Update and new question:

Update -
This below quote is from a recent email I sent out to the s38-m88 Yahoo group;
Note that this is related to the '92 ///M5, not the '91 ///M5 as this thread was addressing.
You'll see the connection though.

'92 S38B36 unstable idle...
A bit of history;
Had a very rough idle, would rev, but after revving when returning to idle would stumble and die.
When left to idle, or feathering the revs back to idle, it would idle but just barely at about 500 +/- RPM.
I swapped out the TPS and ECU, but no improvement. Checked ICV and it appeared to function as it should.
In the course of this work we found when the fuel injector plug rail was moved it would cause it to die immediately.
So we removed and cleaned the injector connectors on both the injector side and the wiring harness side, lots of green corrosion.
After buttoning it all back up he purred like a kitten, idling at about 800 +/- RPM,
and running like the scalded dog he is for a day and a half, close to a 100 miles total driven.

Then yesterday afternoon when leaving work, it started again and got progressively worse at each stop.
Currently it will start immediately but will immediately stumble and die.
If I work with the accelerator it will rev but not super smoothly.
While driving home it would cruise at any speed almost as if nothing were wrong, though I did notice the occasional hiccup.
Last night I worked a bit with the injector harness, but no improvement this time.
I started it this morning, cold start, and same symptom, starts easily but immediately dies.

Any ideas will be appreciated, Thanks in advance...

How many miles on the M5?

Have you ever had the injectors cleaned? Do you have a spare fuel pressure regulator to swap?

Are all ICV hoses and vacuum lines in good shape. Clean the MAF

Might be a MAF on the way out. A quick test is to unplug the MAF and start it up. If it idles fine, the MAF is the culprit.

Miles? = 230K (I have very little service history)

Injectors cleaned? = No, but it has run just perfect up until the rough idle started.

Spare fuel pressure regulator to swap? = Yes I do, so I'll try that tomorrow (it operates almost normally at high RPM).

ICV hoses and vacuum lines = When it first started idling rough, you could open the oil filler cap and/or pull the dipstick and it made no difference.
This I thought would indicate a vacuum leak, but spraying cleaner on all the connections didn't reveal any changes at all.

Clean the MAF = I swapped in the one from our '91 prior to doing the previous injector connector cleaning and there was no change,
forgot to mention that swap in the original email.

Alright Second Responder, you get the "Gold Star for The Day".
I unplugged the AFM (MAF, is there a difference?) and it stumbled at first, but on the second attempt I held the RPM up with the go pedal and then when it returned to idle it was fairly rough, but it did keep its idle. I swapped back in the one from the '91, the one that was originally in this '92, plugged it in and he's purring like a kitten again.

As a side note, when I would drive the '91, and it would rain, it had a habit of running rough, and occasionally it would just flat out die. Well, guess what happened yesterday just prior to my drive home? It rained and the streets were still wet, so I no doubt got moisture up in the AFM area and the ugly, previously undiagnosed problem with the '91 reared its ugly head.

New problem; What to do with this AFM that is moisture sensitive? As long as it is dry outside, it presents no negative symptoms.

Thanks Guys!!!

Question -
What to do with this AFM that is moisture sensitive?
Is it repairable? Where does it need sealing?

Any and all comments appreciated.