dan_a

Hi all,
I have a 2008 525i with rough idle on startup, it seems pretty common on a n53 direct injection engine. (I kinda wish I got a n52 haha).

I have been reading loads of threads on this problem and think I have leaky injector(s). I get really bad rough idle on cold start like the engine is going to stall. If I give it some revs then restart instantly there is no rough idle whatsoever. Would these symptoms likely be leaky injectors? I initially thought it might be the fuel pump but it doesn't make sense as an instant restart doesn't give the same issue. I appreciate any help with this, thanks.

edit: I have had this problem since I got the car a few months ago.

donpb

You could have a vacuum leak.

dan_a

Do you have to get under the car to fix that? Im not able to do work underneath the car I dont have anywhere to do it safely.

dan_a

A forum member posted this somewhere. If it is temperature related I dont think I ran the engine long enough to get up to temperature. I turn on with rough idle, give some revs for about 30 seconds (smell petrol). Restart straight away and no rough idle.

habbyguy

Do you have to crank the engine for a while for it to start, or does it start right up on the first attempt?

dan_a

Im not 100% sure. I will double check in the morning and record the issue.

dan_a

Yes it takes a few cranks to start.

Its a bit of a pain for me to make a video as I don't use a smartphone. For anyone interested BMW Kingston dosent have injectors in stock and they are on backorder until the end of the year. Also why does your car never feel the same when someone moves your seat, I can never get it back how it was.

habbyguy

If you have to crank the engine for a while, I'd suspect a leaky injector. That will bleed your fuel system pressure down (into one cylinder, which isn't good for that cylinder), and your fuel pump will have to go through a few priming cycles to get the fuel pressure up enough to start the car. And then it idles rough because that one cylinder / spark plug is flooded with all that extra gas.

To verify this is what's happening, try turning the car to run without engaging the starter, then off, then back on again - for a few (4-5) cycles. This should build up the fuel pressure, and the engine should start as soon as you engage the starter.

If you're getting a misfire OBD code (P030X, with "X" being the cylinder number) then that's probably the bad injector. Otherwise, you might just spin the motor over for a second or two after it sits overnight, and pull the plugs to see which is drenched. If you can't find an injector, I'd try a used one (making sure that all the part numbers match exactly). The NA cars have much cheaper, simpler injectors than the turbo cars.

dan_a

Thanks for the advice. I will try your mechanical solution to the problem because I am not great with tech. I was considering getting a few used ones on eBay but will check what index I have first and match them. I cant wait until this is fixed then I can fully enjoy my new car after sinking tons of money into it. At least the injectors I can do myself.

habbyguy

The odds are that injectors you get from eBay will be fine (just check the reviews on the vendor to make sure they have a good reputation - no doubt better than the local BMW stealership). ;-)

Again, the normally aspirated engine injectors are a whole lot easier / cheaper than the turbo engine injectors. I was easily able to test mine still connected to the rail by passing 12 volts through them one at a time, using only residual pressure in the fuel system (short squirts, of course). You might be able to do the same, AND see which of them is leaking (should be obvious if it leaks down overnight). Just pull the rail and injectors and if necessary put a shop paper towel under the injector tips to see where the spot forms.