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Rough idle especially when cold

Tiny
CYBAFORGE
  • MEMBER
  • 2003 BMW 325I
  • 2.5L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 140,000 MILES
I get a really tough idle and some knock (to the point of stalling) when the car is cold (but still rough at operating temperature). No knock/problems when it's at high rpm's. There's also a lot of water coming out of the tailpipe upon startup (but almost nothing when it's warm).
I was thinking head gasket but the oil isn't milky.
I'm now thinking it could be a temperature sensor problem? The spark plugs all have similar resistances when I checked and the fuel injectors all work fine.
The fuel is a bit old so I topped it up with some high octane fuel (now it's 1/3 high octane, 2/3 old) so that could be part of the problem?
Just took it for a quick drive and it's getting terrible fuel economy (10L/100 when driving slightly downhill doing 60 kmh at 2,000 rpm's) and stalled when I did a 3 point turn.
I'm getting no smoke, no steam and only some water vapor on startup out of the tailpipe (aside from the aforementioned water).
Thanks so much.
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Tuesday, May 26th, 2020 AT 12:34 AM

27 Replies

Tiny
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  • MEMBER
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Also, there's no bubbles in the radiator from what I can tell.
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Tuesday, May 26th, 2020 AT 3:30 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,874 POSTS
Hi,

This could be a few things. First, is the coolant level dropping? It doesn't have to mix in the engine oil. It can enter the combustion chamber and burn.

As far as the knocking, that is usually the result of timing or can be cause by coolant in the combustion chamber. That's why I asked about usage.

The temp sensor can cause the fuel mixture to be off, which can cause the idle issue. However, I don't see how it would cause a knocking.

Have you scanned the computer for trouble codes?

Let me know.

Joe
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Tuesday, May 26th, 2020 AT 8:40 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
Here is a guide to help scan for codes and check for a blown head gasket:

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

and

https://www.2carpros.com/articles/head-gasket-blown-test

Can you please shoot a quick video with your phone so we can see what's going on? that would be great. You can upload it here with your response. Please run down these guides and report back.
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Tuesday, May 26th, 2020 AT 10:33 AM
Tiny
CYBAFORGE
  • MEMBER
  • 13 POSTS
Thank you both so much!
I ordered an OBDII Scanner a month and a half ago but it's been stuck in international transit due to covid-19. Thanks for the guide and I'll definitely scan codes first thing when I get the scanner.
I think the coolant level has been dropping slowly but I'll run the car a bit more to see if it drops further.
I'll also take a video of what's going on when I know more.
Thanks again.
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Tuesday, May 26th, 2020 AT 5:23 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
Please let us know what you find. We are interested to see what it is.
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Friday, May 29th, 2020 AT 10:38 AM
Tiny
CYBAFORGE
  • MEMBER
  • 13 POSTS
Will do! I'm very keenly waiting my scanner.
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Friday, May 29th, 2020 AT 6:00 PM
Tiny
KEEPITSIMPLE1
  • MECHANIC
  • 17 POSTS
CYBAFORGE:

You did not mention if the "check engine" light is on. I can think of two things off the top of my head: EGR (Exhaust Gas Recirculation) or IAC (Idle Air Control). I believe your vehicle has an IAC valve. The IAC valve is responsible for controlling idle. It's possible for a bad IAC not to set a code. EGR is another possibility. At WOT (Wide Open Throttle) there isn't enough vacuum to open the EGR valve,

Right now, I can't help much more than that. Disconnect the vacuum hose on the EGR valve and plug it and see if it idles better. An open EGR valve supports the more water at the tail pipe too.

Lets hope you checked the PCV valve and for vacuum leaks.

AutoZone does free scans,

I've seen no codes and a bad IAC. See if the idle increases when you turn on the air conditioning. The IAC should be responsible for doing that.

An EGR problem that I trouble-shot drove me nuts, This particular vehicle I was working on was designed to open the port to EGR valve when the ignition was on, When the ignition was off, the EGR got full vacuum. By design this prevented engine run-on. The exhaust and intake manifolds were connected together and the engine could not run in that state so it stopped.

That solenoid was installed in a bad place, The car had rough idle if you started it 20 minutes after the car cooled down from operating temperature. It had a very short time window where it would stick.

It may not be the EGR valve, but it could be whatever is controlling it. I don't yet have the ability to assess my confidence level for your particular vehicle.

I hope something here helps.
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Saturday, May 30th, 2020 AT 5:12 AM
Tiny
CYBAFORGE
  • MEMBER
  • 13 POSTS
Thank you so much for your reply!
The check engine light isn't on but it's running so poorly that I have to believe the light is broken (or since I bought it from a mechanic he cleared it? Not sure how that works exactly)
Unfortunately it's not registered so I can't legally drive it right now.
I'll definitely check how it respond to the A/C, thank you!
I really thought it was the EGR valve for ages until I became convinced that the petrol e46 don't have them. They do have secondary intake valves/pumps but mine seems to be missing (but apparently you can do that).
I'm quite out of my depth so if I say anything that doesn't make sense please let me know but thank so you much for your time!
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Saturday, May 30th, 2020 AT 5:26 AM
Tiny
KEEPITSIMPLE1
  • MECHANIC
  • 17 POSTS
From what I can tell "they" call it an air diverter/bypass valve and the p/n changed sometime during the year so the replacement will be VIN specific.

Definition:
The diverter valve, also called the air diverter valve, are part of your vehicle's emission system. Air diverter valves recycle exhaust and engine gases to lower the amount of emissions into the air by taking pressurized air from the air pump and diverting it to the exhaust manifold. If you notice that your fuel economy is reduced or your engine runs rough while idling, you may need to check your diverter

That sounds like an EGR valve to me except it's using high pressure air. Hopefully one of the other experts can post a nice picture for you.
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Saturday, May 30th, 2020 AT 7:14 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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Can you please shoot a quick video with your phone so we can see what's going on? That would be great. You can upload it here with your response.
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Saturday, May 30th, 2020 AT 11:23 AM
Tiny
CYBAFORGE
  • MEMBER
  • 13 POSTS
Thanks for all the help!
I've attached some stuff:
Some photos of what I think are disconnected (temperature?) Sensors on top of my engine?
One photo of some attached sensors on the side of my engine
A video of me starting the car a few hours ago:

0:00 - Car starts and immediately stalls.
0:11 - I press the accelerator so car doesn't stall and keep my foot there.
0:17 - The revs drop even when the pedal is constant.
0:19 - I press the pedal more to keep the revs up.
0:30 - I press it some more to test the high revs.
0:38 - I try to see if it will idle without the pedal but it stalls.
1:16 - Ignore me pressing the radio.
2:10 - It finally stalls by itself!
2:30 - I move the car around a bit (reverse first).
2:47 - I go forwards.
2:56 - It stalls going up a tiny slope.
3:20 - Back to where I started, back in park (such a low idle :c).
3:45 - More testing the high revs.

And finally a video of me playing with the A/C while it idles (it started up perfectly somehow and got a bit worse over time)
If it's relevant it's about 15°C (or 60°F) and I'm not that far above sea level.
Thank you so much!
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Sunday, May 31st, 2020 AT 3:23 AM
Tiny
KEEPITSIMPLE1
  • MECHANIC
  • 17 POSTS
Try disconnecting the MAF sensor.
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Sunday, May 31st, 2020 AT 8:46 AM
Tiny
KEEPITSIMPLE1
  • MECHANIC
  • 17 POSTS
IAC: You can also try disconnecting this electrically. The idle might stabilize at a higher RPM. Disconnect and re-connect with the car off.

The MAF sensor sometimes does not set a code. With it disconnected, the car generally is driveable, but not quite right.
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Sunday, May 31st, 2020 AT 3:42 PM
Tiny
CYBAFORGE
  • MEMBER
  • 13 POSTS
Disconnected the MAF sensor and it runs much better! High idle but much less of a problem. Should I be getting a can of MAF cleaner?
Should I still try and disconnect the IAC valve? (Do you mean just unplug it and plug it back in immediately while the car is off or actually trying to run the car with it unplugged?)
Thanks!
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Sunday, May 31st, 2020 AT 5:06 PM
Tiny
CYBAFORGE
  • MEMBER
  • 13 POSTS
Update:
Bought some MAF cleaner and cleaned my sensor, let it dry then put it back in and was a bit better than before (didn't immediately stall) but still a rough, low idle.
Unplugged the sensor again and back to  900 rpm idle.
I think I'll try and clean it again with more cleaner and let it dry for even longer too.
Also will try and reset idle rpm's if I can do that and drive it around a bit to see if it gets needed some time to get used to the clean sensor.
If not I guess I'll buy a new MAF sensor.
Thanks again for all you guy's help and please let me know if you have any suggestions!
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Sunday, May 31st, 2020 AT 8:29 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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Once the sensor is too far gone cleaning will not help. did you check for a vacuum leak that will cause it as well. here is a guide to help:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Please run down this guide and report back.
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Monday, June 1st, 2020 AT 10:10 AM
Tiny
CYBAFORGE
  • MEMBER
  • 13 POSTS
When I remove the MAF sensor, it doesn't have any of the problems - could it still be a vacuum leak?
Thanks
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Monday, June 1st, 2020 AT 5:33 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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It sounds more like the sensor is bad, I would try a new one. You get that scanner yet? It might have a code for a bad sensor. Here is how to replace the MAF. Check out the diagrams (below). Please let us know what happens.
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Tuesday, June 2nd, 2020 AT 1:50 PM
Tiny
CYBAFORGE
  • MEMBER
  • 13 POSTS
Thank you!
Unfortunately the scanner hasn't come yet.
I'm going see if I can get a second hand a scanner for cheap.
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Tuesday, June 2nd, 2020 AT 4:48 PM
Tiny
KEN L
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  • 48,363 POSTS
Sounds good, let me know.
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Thursday, June 4th, 2020 AT 11:43 AM

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