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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Sun, Dec-02-2018, 07:11:28 PM   #1
Nate047
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Default Help with rough engine at low RPM

Hey all, so I recently bought a 89k mile 2001 Imola 6MT coupe from out of state, paid a low/fair price, but of course there are some issues... Maybe you guys have some input on this.

The car idles a LITTLE rough. It's not misfiring, and the idle doesn't fluctuate up and down. It's just not as smooth and buttery as it should be, especially when you drive it back to back with another M3. There's like a bit of hesitation in the lower RPM band until about 2000-2500. It feels kind of like a timing issue. To be honest it's so subtle I didn't even really notice until my friend Marc said something.

He and I did a compression test, the results were lower than we expected but all within range of each other...? They were 120, 125, 125, 120, 125, 125. TBH this concerns me but we then did a leak down and each cylinder was at just 2% or less. Slightly mystified at this point, we pulled the fan off thinking maybe there was a vibration coming from a broken fan, no change. The car is not down on power.

We are thinking it could be related to the valvetrain. But before we crack into that, is there anything auxiliary you guys would check/clean/etc...? Pulleys and tensioners have been done recently, I'm doing the alternator, and we are pretty sure the VANOS was done at some point but not by the previous owner (history before him is unknown) Plugs have also been done recently. One of the coils is different than the other 5, but again no codes, no misfire... Yet at least lol.

Thanks in advance!
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Last edited by Nate047; Mon, Dec-03-2018 at 03:55:52 AM.
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Old Sun, Dec-02-2018, 07:55:26 PM   #2
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Default Re: Help with rough idle diagnosis

I would hook up a scanner and look at the live fuel trim, inpa would be best, but a general scanner with fuel trim data, and go from there. It could be something as simple as a vacuum leak. But looking at the fuel should yield some information.

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Old Mon, Dec-03-2018, 12:59:32 AM   #3
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Default Re: Help with rough idle diagnosis

Good call on the live data. Here's what I'm seeing for fuel trims and spark advance. This look normal...?

FT
Idle https://flic.kr/p/RbBrFL
1k https://flic.kr/p/2axNHNq
1500 https://flic.kr/p/2deUuV5
2k https://flic.kr/p/2axNHKj

Spark
Idle https://flic.kr/p/2bVLgHP
1500 https://flic.kr/p/2deUuH1
2k https://flic.kr/p/2deUuCG
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Old Mon, Dec-03-2018, 01:14:21 AM   #4
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Default Re: Help with rough idle diagnosis

Those fuel trims, <5%, i would consider normal.

Vanos you think was done at some point, approx how many miles ago? Might need to recheck some of the seals. What about a valve adjustment?

How old is the fuel pump/filter/regulator?

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'85 528e 164k miles (sold)
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All DIY: VANOS, WPC rod bearings, full SS (SS stepped V1 headers, catted S1, stock S2, SS sport), AFD E85 Proflex kit, Ohlins R&T/Swift 448f 672r/GC street tops and camber plates, 330 ZHP steering rack, diffsonline 4.1 diff with rem polish, E60 short shifter lever, AKG black diff bushings/subframe bushings, Rogue rtab, Sachs clutch/flywheel, rear main, Beyer driveshaft, valve adjustment, cooling refresh.

Happy to help with VANOS or any other DIY job around NorCal
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Old Mon, Dec-03-2018, 01:18:05 AM   #5
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Default Re: Help with rough idle diagnosis

Also, I'm making an assumption we are not trying to fix an idle issue, all M3s idle rough. I'm going off your comment about hesitation below 2500rpm, which is different from idle.

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'85 528e 164k miles (sold)
'05 M3 6MT coupe

All DIY: VANOS, WPC rod bearings, full SS (SS stepped V1 headers, catted S1, stock S2, SS sport), AFD E85 Proflex kit, Ohlins R&T/Swift 448f 672r/GC street tops and camber plates, 330 ZHP steering rack, diffsonline 4.1 diff with rem polish, E60 short shifter lever, AKG black diff bushings/subframe bushings, Rogue rtab, Sachs clutch/flywheel, rear main, Beyer driveshaft, valve adjustment, cooling refresh.

Happy to help with VANOS or any other DIY job around NorCal
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Old Mon, Dec-03-2018, 01:59:59 AM   #6
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Default Re: Help with rough idle diagnosis

The only thing I noticed is your "TP" values are 0%. It can't be 0% if it is at 2000rpm? Or I'm I looking at something else?

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Old Mon, Dec-03-2018, 03:53:50 AM   #7
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Default Re: Help with rough idle diagnosis

Thanks guys, yea so maybe the title is misleading, it's not really an idle problem. It's more accurate to say the engine is a bit rough and shakes the car a bit more than it should, in the low RPM range. Above about 2k-2.5k it's business as usual from what we can tell.

The service history of the car from new to like 87k miles is unknown aside from CarFax which is pretty much useless. We think the VANOS has been serviced because it's seeping slightly from the front, presumably a bad gasket. So I don't think it's original VANOS. Marc also said this rough engine behavior could be related to valve shims, and I'm gonna be doing an adjustment regardless since I don't know how long it's been since the last one. TBH I am thinking about redoing the VANOS again with a Beisan kit since I really don't know what was done or how long ago. I have a Dr. VANOS on my E36 but their S54 2k price tag is a bit hard to swallow for a street car...

What's the typical age or mileage for fuel pumps to start to go on these cars? Fuel filter and FPR are on my list.

I don't know why the throttle position wasn't registering, that's weird to me too.
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Old Mon, Dec-03-2018, 04:50:36 AM   #8
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Default Re: Help with rough engine at low RPM

I know some pids have a rough time showing proper values. When I was trying to get some pid logging for my tuner, a lot of tools I used failed to provide accurate info for throttle position...so I would not worry about the value of 0.

You dont need 2k to rebuild VANOS, a quarter of that should cover it for all parts. Guessing that it was done - might as well assume it was not. Read this procedure, it lists all the parts you need and how to do it.
http://www.beisansystems.com/procedu...anos_procedure

Also, can you confirm where you see VANOS leaking? That could be the pressure escaping that you need for it not to hiccup.

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'85 528e 164k miles (sold)
'05 M3 6MT coupe

All DIY: VANOS, WPC rod bearings, full SS (SS stepped V1 headers, catted S1, stock S2, SS sport), AFD E85 Proflex kit, Ohlins R&T/Swift 448f 672r/GC street tops and camber plates, 330 ZHP steering rack, diffsonline 4.1 diff with rem polish, E60 short shifter lever, AKG black diff bushings/subframe bushings, Rogue rtab, Sachs clutch/flywheel, rear main, Beyer driveshaft, valve adjustment, cooling refresh.

Happy to help with VANOS or any other DIY job around NorCal
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Old Tue, Dec-04-2018, 01:47:28 AM   #9
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Default Re: Help with rough idle diagnosis

Thanks for the info, the VANOS is seeping from the front, between the main housing and the solenoid. Sorry but I don't have any pictures!
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Old Tue, Dec-04-2018, 02:04:03 AM   #10
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Default Re: Help with rough idle diagnosis

Quote:
Originally Posted by Nate047 View Post
Thanks for the info, the VANOS is seeping from the front, between the main housing and the solenoid. Sorry but I don't have any pictures!
Sounds like you def need to replace sealing plate seals.

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'85 528e 164k miles (sold)
'05 M3 6MT coupe

All DIY: VANOS, WPC rod bearings, full SS (SS stepped V1 headers, catted S1, stock S2, SS sport), AFD E85 Proflex kit, Ohlins R&T/Swift 448f 672r/GC street tops and camber plates, 330 ZHP steering rack, diffsonline 4.1 diff with rem polish, E60 short shifter lever, AKG black diff bushings/subframe bushings, Rogue rtab, Sachs clutch/flywheel, rear main, Beyer driveshaft, valve adjustment, cooling refresh.

Happy to help with VANOS or any other DIY job around NorCal
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Discussing Help with rough idle diagnosis in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)