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      11-07-2016, 07:16 PM   #1
rusty_sojah
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need help, rough idle replaced plugs & coils

2004 z4 3.0i (with sport)

about 2 months ago I was on my way to a 'spirited' car meet and drive event so I filled up with some of Japan's (I live in japan btw) finest 102 octane gas (the good stuff) and then proceeded to tear up the pavement for the next couple hours. All was good until I was on my way back and noticed a check engine light however I experienced absolutely zero issues for the following month, just the annoying light.

after about a month on cool starts it would idle a slight bit rough for a minute then all was fine. This has gotten worse and I figured just plugs needed to be replaced since the car was at around 70k miles on original plugs. in the days leading up to me finally replacing them occasionally I would get a harsh shake and a knock when starting it up and idling.

Last night I replaced the plugs and coils with some ngk and high performance coils from Bavarian Autosport.

Now this morning I am still experiencing the rough idle/small knock plus when I really put my foot down in 2nd I get a weird lack of power around 3-4k RPM's (which I noticed in the days leading up to changing the plugs/coils as well).

What are the likely culprits at this point? Only other performance mod is the AFE CAI at about 20k miles earlier.

thanks for the assistance!
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      11-07-2016, 07:33 PM   #2
Mike_Z4M
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I've seen similar issues on a few BMW'S with the 3.0, 2.5 engine. Thus isn't 100%, but what it possibly could be is your air hoses. From he airbox, Pcv, intake manifold. I've personally found 3 cars with this exact issue and it happened to be a leak. I replaced all three air hoses, Pcv hoses and intake manifold gaskets. Cars idled and drove great. But then again it can be a fuel issue or something completely different. IF you haven't, I recommend connecting a scan tool and seeing what codes it's throwing, that way it might guide you to the source, then post it here if you'd like so we can help better diagnose it.

Last edited by Mike_Z4M; 12-01-2016 at 08:24 PM..
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      11-07-2016, 07:38 PM   #3
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yeah I was sure someone would say to get the code scanned. only problem is that I would have to take it to the Japanese bmw dealership I guess and it will sort of be a pain. not sure what they charge just to tell me the code it is displaying.

is there a specific code that corresponds to the PCV hose replacement issue?
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      11-07-2016, 08:08 PM   #4
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so now that I remember, shortly after buying it about 3 years ago it had a small oil leak out of one side of the manifold so I bought and replaced the intake manifold gasket at that time and never have I seen the small leak since.

going to try to find a place that can read this code and see about replacing the pcv hose as well if it is an easy fix.
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      11-08-2016, 12:14 AM   #5
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Any local mechanic shop that has a scan tool can read the codes, doesnt have to be BMW specific. If I were you I would just check all the hoses that have to do with air, step by step. Open the hood, give it a very small amount of throttle, if theres a LOUD whistle, that can be it. Note that, that engine does have a normal regular whistle which isnt loud at all, but if there is a loud one, that can give you a better idea if theres a leak or not. Or what I do is start the car when cold, and carefully move around air hoses and see if the idle fluctuates. Be careful of moving parts though.
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      11-08-2016, 01:40 AM   #6
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okay found a guy who had the Japanese bmw specific error code reader; as the normal bmw one won't work on a Japanese market bmw, go figure.

error codes:

3C1D Crank Sensor
2883 Fuel trim Bank 2
2882 Fuel trim Bank 1

2783 Air Flow / temp

Egs Trans??

ABS
5e21/24 Pressure sensor
5DA1/A3 Wheel sensor
Power Steering


So I hadn't driven the car in almost 2 weeks till this morning and I noticed that the steering wheel wasn't returning to normal after driving out of a turn like it normally does and it felt like the power steering was not working correctly... wow all of the sudden this car is having a whole bunch of issues.
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      11-08-2016, 02:09 AM   #7
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Welcome to European cars, just have them all cleared and drive the car a little more to see how it performs and if the light comes back. Check all fluids etc aswell.
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      11-08-2016, 11:22 AM   #8
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^WHS
Some of those codes may have been transient from a long time ago.
Clear the codes to get a clean read. Hopefully only 1-2 will come back, and you'll have a better idea what's going on.
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      11-09-2016, 07:27 PM   #9
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so the dude cleared out all the codes, most if not all came back on my drive home.

then I took apart and cleaned the MAF. it did seem to noticeably help the rough idle on startup and the 4-5k rpm lag, by about 50%, but still all the lights on my dash.

the only remaining thing left wrong (aside from all the lights on the dash) that I notice and feel is the lack of power steering. I can live with it and probably will for a while, but when exiting a turn my normal reaction is to allow the wheel to correct it self but now I find I am briefly forgetting this at time and having to just be extra hands on with the steering. I never realized how much the power steering helps you keep the car going straight down the road and helps you come out of turns more easily (aside from the obvious on a car with super heavy turning due to no power steering)...
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      12-01-2016, 08:06 PM   #10
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I was able to see that my intake throttle body housing https://www.amazon.com/dp/B00FFV17U6...657650_TE_item

had holes and was falling apart so I ordered and installed a new one. now I have no more rough idle or hesitation at 4-5k RPM's.

only problem now is the power steering, wish me luck!
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      12-01-2016, 08:24 PM   #11
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Nice! I knew it had to do with some kind of intake tubing.. Goodluck with the power steering!!
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