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Old 04-15-2019, 12:36 PM   #1
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Rough idle/power loss

Hi all,

Although this is my first post, I have been using this site as a reference for a while now!

I have a 2002 318ci (n42 engine) automatic.

Iíve got an issue thatís now really bugging me!

The problem started about 2 weeks ago when my alternator packed up whilst driving home along the m6. Before this I havenít had any issues with the car apart from a small oil leak which Iíve been meaning to sort (I have a newborn so this stuff has been put on the back burner recently).

Car got recovered, took it to the garage who sorted the new alternator for me and got it all fitted. Great, job done. Driving it home, car felt fine and didnít think anything else of it.

The next day on my way to work, the car was really struggling to stay alive whilst waiting in traffic/at lights. On 2 occasions it actually died but started up again first time. I also noticed that pulling out of junctions the car was really hesitant and then would just kangaroo down the road for a a few seconds before kicking in properly and taking off. It does this now in the first few gears, and only seams to happen once the car has warmed up.

Now, Iím no mechanic, but do like to try and find issues and fix them for myself if I can, so looked on YouTube at some videos, read some posts on here and came to the conclusion that it could either be a vacuum leak or bad spark plugs. Iíve now changed my spark plugs and looked at the air intake boot for any potential leaks.

First thing I noticed was at the top of the intake boot there is a slight tear. New boot has been ordered. I also noticed the the massive rubber o ring between the boot and MAF is shredded. So Iíve ordered a replacement part for this too.

Now after changing the spark plugs, there is an improvement on the overall drive, but my issues of a rough idle and the car jumping forward hesitantly in the first few gears still remain. I know Iíd need to wait until my new parts get here to rule out a vacuum leak, but Iím now starting to think this could be a fuel issue?

Thereís a small air release valve on the top of the the fuel rail, and when pushing that in, fuel sprays all over the place. I also ran the car up to the petrol station to put in some fuel (as it was very low and I was rulling out simple options) and literally every couple of seconds the fuel pump would click as if the tank was full!? I tried different positions, and noticed when I was pulling the fuel pump out, fuel was backed up and leaking out before the fuel tank closed again? I know this could be unrelated, but was just very coincidental.

Has anyone else had this issue before? I know thereís lots of threads on here with similar issues, but I just havenít found an answer yet!

I have now check engine lights on my car, and have yet to get it plugged in as I know this alone is going to cost me more money. It will be my next step, but I just wanted to see if anyone could help me in here first.

I do have photos/videos of some of the issues Iíve found, but have not yet figured out how to upload them in here!

Thanks in advance.
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Old 04-15-2019, 05:10 PM   #2
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Fit the new parts you have coming. You've done good to find these problems.

Buy a code reader so you can check your codes yourself. Best bet is a ODB2 to WiFi or Bluetooth (depending on your phone) emulator and the ODBfusion app.

Post the codes here so we can help you with the specific faults that they show.

Last edited by NZ00Z3; 04-15-2019 at 05:11 PM.
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Old 04-16-2019, 08:48 AM   #3
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That ďair release valveĒ is actually a fuel pressure test port! The fuel pressure has to be at least 50psi at all engine speeds and loads. If the gauge (taped to the windshield/windscreen so you can read it while driving) shows anything less the pump is suspect. Also, the fuel filter could be partially clogged.

The problem your having when filling the tank could be any number of things. However, does the problem arise at other gas stations?
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Old 04-16-2019, 09:23 AM   #4
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Very common for pump click off before the tank is full...especially, it seems, in the summer.

...and your known leaks might well be the cause for your as mentioned, replace them first and see where you get.

Good luck!

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Old 04-17-2019, 10:58 AM   #5
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Thanks all for the input. New parts have been delivered today I think, so will get them fitted tonight and hope for the best for now!
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318ci, n42, power loss, rough idle, vacuum leak

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