M42 won't hold idle UPDATE: New problem. Need help

[shameson]

I think the issue was found. Had a spark from near the alternator when it was revving. After pulling the alternator we found a spot where it looks like the ground was arcing causing a mark on surface of alternator.

Had the alternator tested and it was at 14.2. The alternator ground strap probably is the issue. Strap is poor shape with multiple tears in the insulation. Used a volt meter on the battery and was only at 11.75, so there's certainly an issue with alternator charging.

Going to test the alternator with a new ground strap and see what happens. The throttle cable is also in poor shape and will be replace as well

[uturn]

The last time I had a car act like this was because it had a cracked cylinder head.

[shameson]

Sweet, thanks for your input. This gives me a lot of leads to follow up on. The alternator check is a good idea, makes me curious if my new alternator really is the problem all along

[varg]

The failure of the alternator coinciding with this problem may be a red herring. Here are some things you haven't checked by my reading of your thread:
Ignition Timing
Fuel pressure
Fuel injector o-rings
Fuel injector spray pattern (pull the rail out and watch the injectors fire while you have someone crank it, with the coil unplugged)
Intake manifold gaskets, tightness of manifold nuts
Brake booster valve and booster itself (can cause vacuum leaks)
Ground on the battery tray near the firewall (this is the ECU's ground and is important)
AFM connections and condition of wiring/connectors and pins

I recommend putting a couple of gallons of new gas in it then checking these things if the problem doesn't go away. They're all pretty easy to check. If you block the ICV off and prop the throttle open a tiny bit you will be able to eliminate that as a source of problems altogether so it's easy to diagnose. Also verify proper charging system voltage to eliminate the new alternator as a problem, I have seen bad alternator regulators cause very high system voltages and odd problems.

[shameson]

Any update on your progress?

So far no. Drained the fuel tank in case I had bad gas, like water in it. Going to fill up a can of fresh premium and put it in. After talking to others, going to check ground straps next, see if there's a bad ground causing the issue. Part of me does think this is a electronics/power related issue. Still haven't ran the compression test which I will and also having someone come up to help troubleshoot soon.

[mjimport]

Any update on your progress?

[shameson]

make sure the connector on the passenger side firewall is disconnected? you may have inadvertently connected it if you noticed it wasn't before

Nope, never touched that plug prior to this. I wish it was that simple lol

[jrobie79]

make sure the connector on the passenger side firewall is disconnected? you may have inadvertently connected it if you noticed it wasn't before

[shameson]

So yesterday I tried a different ICV, AFM and ecu. Even cleaned my own ICV too. It would fire up fine after sitting, idle fine, and rev up fine, with no missing. But then it would die after a minute or two of running. Once it would die it wouldn't stay idling that long and would start missing at ~ 3500-4000 again. After dying it would cause hard starting, and would barely start again.

Still kinda lost at this point, next thing is that I'm going to give the injectors a cleaning, and hopefully see if I can find out if they are flooding it maybe, causing it to run too rich

Tried it again today and wouldn't even idle. Would die instantly every time

[shameson]

Before you go around messing with the fuel pump, I would take out the ICV. Mine had 2 contacts. Apply 12V to it and you should hear a click. If not, it is bad. My car was doing the same thing. I ended up getting a used one off of eBay for $35. That fixed my problem. Make sure it clicks before installing. Keep us updated.

I'm going to borrow an ICV that's in good order off a friends if I need it

See post #1 for new update

[amit_b82]

Before you go around messing with the fuel pump, I would take out the ICV. Mine had 2 contacts. Apply 12V to it and you should hear a click. If not, it is bad. My car was doing the same thing. I ended up getting a used one off of eBay for $35. That fixed my problem. Make sure it clicks before installing. Keep us updated.

[shameson]

It actually will which is why when you give it gas it doesn't die. It's quite simple just look at your harmonic balancer...... worst case scenario you fried the ecu when changing the alternator.

I tried a spare ecu to be sure, no change

[bmwm42]

It actually will which is why when you give it gas it doesn't die. It's quite simple just look at your harmonic balancer...... worst case scenario you fried the ecu when changing the alternator.

[shameson]

Jaime, have you checked to make sure the harmonic balancer isnt falling apart......if the thing is becoming undone your never going to hold idle. Ive had a car do that before. Anyways you have my number if you need further assistance.

That's an interesting idea...but wouldn't it not run altogether with a failed balancer?

And thanks, if none of the this stuff works I'll have to pick your brain

[bmwm42]

Jaime, have you checked to make sure the harmonic balancer isnt falling apart......if the thing is becoming undone your never going to hold idle. Ive had a car do that before. Anyways you have my number if you need further assistance.