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Old 02-06-2012, 08:00 PM   #1
kitkid
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e34 4.0L slightly rough idle

Do these engines normally idle just a tad on the rough side or should I look a little deeper?
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Old 02-06-2012, 08:49 PM   #2
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If it's not a misfire and you have no codes, I'd start by looking at your engine and transmission mounts.
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Old 02-06-2012, 09:02 PM   #3
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Ok thanks, the drivers side engine mount is usually the bad one?
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Old 02-06-2012, 09:43 PM   #4
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I'll let E34 V8 experts take that one but if you have any doubts, just change them all. Unless you know they were recently changed, they're probably factory original.
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Old 02-07-2012, 02:12 AM   #5
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It can be frustrating trying to diagnose idle issues on these motors. Check your motor mounts for sure - they are oil filled so if they are wet then they're probably shot. M60s like to eat motor mounts, so they probably are anyway. I remember people on BFC campaigning for someone to make urethane mounts for them, but I had just done mine and didn't follow up on it. Might be worth a search...

Back to the frustrating part - these motors are also known to be really sensitive to vacuum leaks. They'll cause a rough idle and won't necessarily throw a code. Most likely culprits are the throttle body, PCV plate (rear of manifold), and manifold gaskets. Check everything though - intake boot, vacuum hoses from brake booster and charcoal canister, etc.

Are you aware of the Stomp Test? If not, google it and try it to see if you have any stored codes.

Finally, there is the dreaded Nikasil issue, but don't get all fired up about that until you rule out vacuum leaks or maybe a bad MAF, which is far far more likely to be the case.
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Old 02-07-2012, 03:17 AM   #6
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Quote:
Originally Posted by Nick_V View Post
It can be frustrating trying to diagnose idle issues on these motors. Check your motor mounts for sure - they are oil filled so if they are wet then they're probably shot. M60s like to eat motor mounts, so they probably are anyway. I remember people on BFC campaigning for someone to make urethane mounts for them, but I had just done mine and didn't follow up on it. Might be worth a search...

Back to the frustrating part - these motors are also known to be really sensitive to vacuum leaks. They'll cause a rough idle and won't necessarily throw a code. Most likely culprits are the throttle body, PCV plate (rear of manifold), and manifold gaskets. Check everything though - intake boot, vacuum hoses from brake booster and charcoal canister, etc.

Are you aware of the Stomp Test? If not, google it and try it to see if you have any stored codes.

Finally, there is the dreaded Nikasil issue, but don't get all fired up about that until you rule out vacuum leaks or maybe a bad MAF, which is far far more likely to be the case.
my M30 eats the drivers side motor mount twice a year
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Old 02-07-2012, 08:23 AM   #7
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Thanks for the advice. I will try the stomp test. I was also leaning towards vacuum leaks in particular the PVC plate (where to purchase a reasonably price PVC assembly) but will check everything. Will have it on the hoist tomorrow and check the engine mounts (where to purchase). Below is a link regarding "The Nikasil Myth". http://www.meeknet.co.uk/E32/Nikasil.htm
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Old 02-09-2012, 11:33 PM   #8
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Checked the engine mounts today,like new (have been changed recently). This car is new to me, inspection continues. Ordered a pcv from Auto Camping, great deal and overnight service. Quick note, previous owner deleted the muffler and ran straight pipes out the back, cool sound but too loud for my tastes. After replacement muffler installed the idle improved slightly, possibly due to the lack of back pressure?
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Old 02-24-2012, 10:09 PM   #9
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Idle problem solved. Here's what was done. Pcv replaced, slight improvement. Installed new muffler to replace straight pipes, slight improvement. Valve cover gaskets replaced and compression test (180 to 190 all cylinders). Intake gaskets replace, no improvement. Oil fill cap replaced, huge improvement! The gasket was just plain old causing a vacuum leak.
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