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E46 General discussion and technical help for 1999-2004 3 series cars.

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Old 11-01-2009, 03:55 PM   #1
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Engine start problem

Every time I try to start my e46 318i after a couple of hours of being off the revs go up normal but quickly fall till the car shuts down. I have to accelerate the car a little everytime I start the car for the revs to go up and then the revs stay normal. What is the cars problem and how can it be fixed?
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Old 11-07-2009, 02:02 PM   #2
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Could be a number of things but I'd start by checking for vacuum leaks, then move on to sensors, but that would require a scan tool.
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Old 11-14-2009, 09:23 PM   #3
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Where or which parts should I check for vacuum leaks? Intake, where else?
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Old 11-21-2009, 06:03 PM   #4
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Interesting thing happened to me this week. I installed an intake to the car on sunday and this days the car has had an improvement. When I turned the car on, rev went really low and had to start the car again but now when I turn the car on revs still go low and then normal again but doesnt turn off. Does this help a little on figuring out what my cars problem might be?
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Old 11-22-2009, 12:13 PM   #5
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I take that to mean the emissions monitoring functions of the engine management system is hunting for a suitable fuel/air mixture to set the idle, and can't do so, probably because of a vacuum leak, as Big Evil suggested. O2 sensor may also be at play here.
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Old 06-01-2010, 07:13 PM   #6
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I changed 02 sensor and the car is still doing the same thing. I dont have any codes or check engine light on. Also I checked for vaccum leaks and found nothing. What else can I check?

Last edited by DAES; 06-01-2010 at 07:15 PM..
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Old 06-02-2010, 09:56 AM   #7
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How did you check for vac leaks?
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Old 06-03-2010, 10:16 AM   #8
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I took the black rubber intake parts out and checked for holes or any rupture but found nothing. Ive also heard that with the engine running you can spray some 'engine start liquid' while paying close attention to any changes on revs but I dont know if spraying that thing all over can harm some other stuff. I am able to listen to a whistle when I accelerate my car while driving. What should I do now?

Last edited by DAES; 06-03-2010 at 10:21 AM..
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Old 06-04-2010, 01:05 PM   #9
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I might have missed this from an earlier post, but how is the engine at idle? Is it rough or "hunting" when you're at a stop? I had this similar problem and it was my MAF (if you disconnect yours, does the idle smooth out?). I ended up replacing the MAF (even after a good cleaning) and cleaned the ICV just to be sure.

By far, the very best thing you can do here is invest in an OBDII scanner that plugs into your laptop. Just because you don't have an MIL on doesn't mean that you don't have a "pending" code on the ECU. They sell for anywhere between $40 to 200 on eBay. Every DIY'er should have one!!!! Anything that uses the "ELM" chip will do.

Also, the OBDII scanning software will give you live readouts of ACTUAL sensor values so you can, at least, correlate any bogus numbers. This way, you don't blindly go and replace parts and "hope for the best".

Testing for vacuum leaks is best done via "smoke test" at your local mom and pop auto shop. They shouldn't charge you more than an hour's work of labor.

How many miles are on your car? If you're over 100k, then you *may* be due for new pre-cat o2 sensors, but for the most part, those are fairly solid (again the obdii sofware will give you very good indication of any declining health).

Keep us posted!
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Old 06-04-2010, 03:46 PM   #10
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ok after half hour trying to upload some pics I wasnt able to do it sorry. I was looking for the ICV and PCV to clean them that way maybe I can solve the problem, turns out I didnt find the ICV. When I was taking out the PCV saw the hose going to it with a 1.5 inch rupture so I was extremely happy that I found the problem that has been bothering me for a year. For the meantime I sealed the hose with 'black tape' very well. I do feel the car a bit better and heard no whistle but the problem when I start the car is still there.

I did changed 02 sensor. My revs on stop are ok, they dont fluctuate or move at all and dont have rough idle, they stay at like 750-800 rpm, they got better after I changed 02 sensor. But as I mentioned when I start the car after the car has been parked for a while revs go up normal but instantly drop to 500 rpms and go back up and stay normal.

Miles on car 40,000.

Last edited by DAES; 06-04-2010 at 03:56 PM..
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Old 06-15-2010, 10:10 AM   #11
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I had the same problem mine was the idle control valve needed cleaning
I cleaned the valve and the car has been fine since
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Old 06-15-2010, 11:13 AM   #12
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Quote:
Originally Posted by leeella View Post
I had the same problem mine was the idle control valve needed cleaning
I cleaned the valve and the car has been fine since
Turns out the ICV was pretty easy to get to, I was looking at the wrong places. Found it and cleaned it with carb cleaner, it was dirty but made no difference.

I now have run out of things I could look out to. Help people help!

Last edited by DAES; 06-15-2010 at 11:28 AM..
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Old 06-15-2010, 02:22 PM   #13
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Fix the vac leak with a new hose, rednecking it doesn't cut it on these cars. And you need to get a smoke machine hooked up to the vac system to check it completely. You can do it with a party fogger and some rubber hose. MUCH better way of doing it and you will find every leak the car has in minutes.
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Old 06-15-2010, 06:39 PM   #14
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Fix the vac leak with a new hose, rednecking it doesn't cut it on these cars. And you need to get a smoke machine hooked up to the vac system to check it completely. You can do it with a party fogger and some rubber hose. MUCH better way of doing it and you will find every leak the car has in minutes.

Where am I supposed to put the hose at while the party fogger is doing its thing?
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Old 06-16-2010, 09:44 AM   #15
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Use some good grade radiator hose to attach to the party fogger (the nozzles get hot) then a step down bit to force it into a smaller vac line sized hose. You'll want to attach it to manifold vacuum somewhere along the intake after the throttle plate.

Start the fogger look for any smoke leaking out of the system. It there isn't any, open the throttle plate and it will fill the intake lines and you can check those as well. If smoke only comes out the front of the airbox you have a tight leak free system. If not, fix it till it is and you know you got everything so then you can start looking at sensors etc. Cheapest why to find out whats what.

Good luck
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