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7 Series - E38 (1995 - 2001)

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  #1  
Old 06-06-2012, 07:37 PM
Sobek Sobek is offline
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Mein Auto: 1996 BMW 730iL
Rough idle issues - 1996 730iL

Hey everyone,

Thought I'd take a shot at this on Bimmerfest too (I'm a member over on Bimmerforums). Not having much luck sorting this one out so I figure it can't hurt to post the same information somewhere else too - I know a lot of people frequent both forums, but there's always some folk who are exclusive to one or the other - wouldn't mind some fresh ideas!

I should also point out that my car only has 118,000 kilometers on it, so it hasn't been driven to death! Anyway, on to my problem. I'll start with a video;



As you can see, the first start of the day is ROUGH. A month ago it would jump up to 750-800rpm and just sit there, happy as can be. Now it barely hits that cutoff line, and drops low enough that you'd think it had stalled. It pushes through though and eventually reaches a reasonable RPM range, where it generally sits happily from there on out. This ONLY happens on the first start of the day, regardless of temperature or time of day... any subsequent starts during the day, even after hours of sitting in a garage, are all perfectly fine. To give you an idea of what I've looked in to so far, here is a copy of what I've posted over on Bimmerforums so far (no solutions yet, but I'm hoping!!);

1) ICV - cleaned this out a while back as it was pretty gummed up and not moving freely at all. It's now doing its thing perfectly, however this never made any difference to the way the car behaves on its first start of the day. It does hum excessively loud when the key is in POS 2 though, but I'm unsure if it's loud enough to indicate a problem or not. I'm sure it's fine though.

2) Valve Cover Gasket's - these were replaced when I purchased the car months ago as they were leaking oil. There's still some residue making its way into the spark plug wells but it doesn't seem like much. I'd like to think I can trust the work the guys did as they're a great bunch who really know their stuff and have never let us down before... But maybe they just didn't get it quite right and there's an issue with the gaskets being a bit leaky? I would have thought new VCG's should result in NO leakage into the plug wells?

3) Plug wells! I just recently (3 weeks or so ago) cleaned up all of the oil around the spark plug wells, cleaned the boots, added o-rings to properly seal them, and put it all back together. Can't really say it made any difference, as the car was warm at the time and it drove just as good as ever. Some oil has made its way back in again - see point 2 - could failing spark plugs cause a rough idle after the car has been sitting overnight? Everyone tells me 'no', but I can't help but think that oil around the spark plugs must cause SOME problems?

4) Vacuum leaks. I honestly cannot find any more! I repaired one rooted hose going into the air pump vacuum control valve (made no difference). I also replaced the small vacuum line going from the OSV (PCV) into the fuel pressure regulator valve (this actually seemed to do wonders for my idle performance, but only for a few days!). I have also replaced the diaphragm on the OSV (PCV) recently, however the existing one wasn't TOO bad and I couldn't tell a difference, but it did cut the gurgling at the oil dipstick down a bit (the original diaphragm had no tears or splits, but the white rubber 'teeth' were completely dissolved and like brittle cardboard). I've gone over every hose and pipe I can find with a fine tooth comb and can't find any other leaks. There could be some hoses buried down the back of the engine I've missed but I 'fingered' them all best I could and nothing seems amiss - no hisses or suction to be heard.

5) Misc / Additional - I have checked my MAF and it seems to be functioning perfectly, but I did clean it (INPA readouts look good for voltage and airflow readings - I think ). I have checked all of the boots on the intake and they're solid as a rock, no splits or leaks. I also have a new fuel filter waiting to go on - could a clogged fuel filter cause this kind of idle roughness? I have no idea how old the existing filter is and won't know until I take it off. We also had two brand new BOSCH post-cat o2 sensors installed shortly after buying the car as they basically went kaput one day out of the blue, so they shouldn't be a problem. Also, the car is not throwing any codes, and no CEL or SES lights have come on at any stage at all. I DID have a couple of codes recently from INPA for '201 Lambda Regulator Bank 1' and '203 Lambda Regulator Bank 2' which was VERY vague, but I cleared that and it hasn't come back. I suspect this code came up because I bypassed the solenoid on the emission control vacuum line; Part 1 on this page - http://realoem.com/bmw/showparts.do?...43&hg=11&fg=45 - since I reconnected that solenoid and cleared the codes, they have not returned. Butterfly valve in the throttle body is clean and moving freely too.

I've just installed a new Throttle Position Sensor for the hell of it and that's made no difference to anything, but I was happy to do it (one less thing to worry about!0. There's no particularly odd noises coming from the engine and once this idle smooths out, the car operates beautifully.

Can anyone suggest any other things I can investigate? It basically just started doing this one day but I can't really pinpoint any specific time it started, nor do I recall doing anything to the car just prior to it starting. I'm stumped! I bet my own ass it's going to be some mind numbingly simple thing that's causing this, but I must be missing it somehow. Ask any questions and I'll respond as to whether or not I've investigated it so far!

FYI, it's been a week since I reset those 201 & 203 Lambda Regulator error codes. I just hooked it up to INPA the other day, and it came up all clear. I'm 99.99% positive it was just because I had that solenoid bypassed.

Appreciate ANY help guys!

Last edited by Sobek; 06-06-2012 at 08:46 PM.
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  #2  
Old 06-07-2012, 06:08 PM
Sobek Sobek is offline
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Mein Auto: 1996 BMW 730iL
Ok, interesting change of scenery this morning... Turned it on, tapped the gas (to try and overcome a bit of that initial sputteryness) and instead of a drastically low RPM it just shot right up to about 3000 or so and held it there. I gave it a slight tap on the accelerator, and all that did was make it start climbing some more. It hit almost 4000rpm before I turned it off. I went into the engine bay and checked around - from what I can tell, the Cruise control throttle cable mount was a bit dodgy and when you tap the gas pedal, it would get stuck out of the guide (hard to explain). Could that Cruise Control cable make the idle stick high? I thought it was only factored in when Cruise Control was actually turned on? Anyway, fixed that. went to turn it on again, and no dice! It cranks and cranks and cranks, but won't turn over.

Normally I'd jump straight to Camshaft sensor but, I wonder if this is in any way related to the rough idling I've been having on these first starts of the day. I'll be ducking back a bit later to try and check for codes as I'm at work right now (It won't be easy, it's sitting out in the rain and I obviously can't drive it into cover!!!) but knowing my luck, everything will report NO PROBLEMS CAPTAIN.

Thoughts?

Last edited by Sobek; 06-07-2012 at 06:13 PM.
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  #3  
Old 06-07-2012, 09:46 PM
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joyism5 joyism5 is offline
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Is your engine a straight 6? Do you know the code for that engine? There are not many guys around here with the 730 on the E38. Actually there is one with nice knowledge, from UK, I forgot his name.... look around the threads you'l find it for sure. I think here(USA) you can find it only on 3 & 5 series. Maybe if you post the problem on the section with that particular engine you will get more answers. Just an idea, I don't want to scare you away.
Back to the issue, since is happening only to a cold engine I would suspect :
-secondary air pump injection because that kicks in only on first start, only in case your car is equipped with. Here the 96 E38 are not, but maybe yours is since it has a different engine
-oxygen sensors, when engine is stone cold, the info from one of them sends the readings to the DME where the math is getting done to get the fuel/air ratio. I think the pre cat sensor does that. Since your's is new I would make sure is the right one there.
-cat converter also plays a role since is running at the best once is hot.
-you have to have a system that supposed to kick your rpm to higher rate than normal on cold start, this is where I search into, but I can't say which one is since you have a different engine.
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Old 06-07-2012, 11:11 PM
Sobek Sobek is offline
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Hey joyism, thanks for the reply. My engine's a V8, 3.0L. Regarding your points, here are my observations so far;

1) The secondary air pump seems to be doing its thing just fine. I can hear it run for the first minute and it sounds completely normal and functional... No reason to suspect it's at fault at this stage I feel.

2) Regarding the O2 sensors - I've only had the post-cat sensors replaced, as the pre-cat's were functioning normally. I understand they're probably right at their 'end of life' period, so they might be something I'll look into very soon. I haven't pulled the codes yet today so I suppose if they've completely had it I might get lucky and find something to indicate so.

3) Haven't got a look IN the catalytic converters yet, however I can't find much reason to suspect they're at fault. No odd noises or rattles from them, and to date no error codes, SES, CEL or anything to indicate they might be blocked or failing. Won't rule that out though!

4) As far as the idle RPM goes, you're right, it does idle higher than usual on a cold start which is all good. Obviously it should only be 700-1000 and not the 3000+ it did today haha!! Still I think that was a one-off thing from the throttle cable. My Idle Control Valve seems to be working well, and there are no detectable vacuum leaks anywhere in the 'loop', so it's got me a bit miffed.

Someone suggested I may have a vacuum leak somewhere where the vacuum lines run into the car and into the dash... It might explain why I occasionally hear a slight 'bzz' sucking sound from INSIDE the car, and why all of the vacuum lines instantly relax as SOON as the car is turned off. Might be a big leak there somewhere but for the life of me I can't find any hoses in there that run into the car... Realoem's diagrams aren't too helpful there either.

Going to get this bugger sorted if it kills me
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  #5  
Old 06-08-2012, 02:58 AM
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PETER NEWMAN PETER NEWMAN is offline
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Smile Rough idle

I could be the guy from the UK, My name is Peter Newman and I'm on this site, A problem which I've come across many times is the vacumn block which is bolted to the rear of the inlet manifold, It's a rectangular item and it's held on with torx bolts and they can be a devil to undo, When this unit starts to fail you can get tickover problems, It's worth replacing anyway, Peter
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Old 06-08-2012, 05:04 AM
Sobek Sobek is offline
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Quote:
Originally Posted by PETER NEWMAN View Post
I could be the guy from the UK, My name is Peter Newman and I'm on this site, A problem which I've come across many times is the vacumn block which is bolted to the rear of the inlet manifold, It's a rectangular item and it's held on with torx bolts and they can be a devil to undo, When this unit starts to fail you can get tickover problems, It's worth replacing anyway, Peter
Are you referring to the OSV? (or PCV depending on who you talk to). I actually just cleaned that out and replaced the diaphragm / vacuum hoses a little while back, for good measure. It was in pretty good shape all things considered. My car's only done a about 118,000kms so it's mostly in good condition parts-wise.

Last edited by Sobek; 06-08-2012 at 05:06 AM.
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Old 06-08-2012, 08:47 AM
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Quote:
Originally Posted by PETER NEWMAN View Post
I could be the guy from the UK, My name is Peter Newman ...
Yeap, you'r the man!
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  #8  
Old 06-08-2012, 08:51 AM
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I don't know about the vacuum leaks... If the engine is going to such a high RPM, the DME should throw out a code ...my opinion. Actually I'm surprised that the DME is not throwing out a code yet.
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Old 06-08-2012, 05:40 PM
Sobek Sobek is offline
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I may have an idea as to what's happened, but I won't be able to confirm until tonight when I can get back to it. It's a bit convoluted to try and explain through simple text, but basically I think that dodgy cruise control cable guide is all to blame. I was thinking over everything again and I realised I tapped the gas as soon as I turned it on that day, as it really helps it get over that initial rough idle. What I believe happened was I turned it on, tapped the gas which knocked the guide out, locking the RPM at a certain level. I then tapped the gas to see if I could get it to 'kick down' and get over it, but as the cable was likely stuck, all that did was increase the RPM with very little consequence. I turned the engine off, thought about it for a bit, then turned it on again only to find it was still doing it (blissfully unaware of the throttle cable situation). Turned it off not too long after and went to inspect the engine bay.

I believe at this point, I've just flooded the engine. Now that I've fixed the throttle cable, I should be able to use some common sense to get it going again if it definitely IS flooded. My only concern is that if those high RPM's were being caused by something else entirely (which isn't throwing ANY codes, bastard of a thing) then it may just wind up doing it again after I get it going. That's what I'm worried about... Last thing I want to do is throttle the living hell out of the poor thing on a cold start!

So we'll see what happens tonight. I'll check the spark plugs and such for any traces or smells of fuel to indicate flooding, and take a stab at getting her going again. At that point, well... we'll see!
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Old 06-08-2012, 09:32 PM
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If that's what cause such a headache...
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Old 06-10-2012, 07:47 AM
Sobek Sobek is offline
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...That is indeed what was causing such a headache. Took a bit of doing but got her going again and all is back to normal. Well, I suppose I'll see tomorrow if it's still got the rough cold start but at least it's driving again!
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Old 06-11-2012, 06:49 PM
Sobek Sobek is offline
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FYI, the rough as guts cold start is still there, exactly as in the original video I posted. As soon as I start the car it's just chugga chugga until it 'builds up' (vacuum you think?) and mostly gets over it. I can tap the gas a bit here and there and keep the revs where they should be, so it's not physically incapable of sustaining idle RPM while it's having troubles.

Someone suggested that due to the vacuumey sucking sounds I can hear from behind my dash when I first turn it on (that kind of bzzeek bzzeek sucking sound as the vacuum starts to happen) might indicate a vacuum leak in one of the hoses that leads INTO the dash from the engine bay. Any ideas what those hoses might be or where I could find them / get to them?

This is driving me nuts and I want to get the poor thing fixed
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