E30 325i engine shudder

Hi all, I have just recently bought another E30, a 1991 325
convertible to replace the 320 i already have. The new car runs
perfectly when driven but at idle there's a bit of a shudder from the
engine every now and then. You can feel it shaking the car a bit when
sat in a traffic jam for example, not constantly, just a few shudders
every 10 seconds or so. I replaced the rubber engine mounts to see if
they were to blame but it made no difference. The idle speed stays
totally constant even when it shudders. With the engine running and
the bonnet up, you can feel and see the shudder while at idle although
you can't really hear it, no change of engine note or anything. Once
driving the engine runs perfectly.

The car's done 97000 miles and had a full service/inspection 2 just
before I took ownership. Has anyone experienced a similar problem with
M20s or have an idea what it could be?

Thanks

Mark

> Hi all, I have just recently bought another E30, a 1991 325
> convertible to replace the 320 i already have. The new car runs
> perfectly when driven but at idle there's a bit of a shudder from the
> engine every now and then. You can feel it shaking the car a bit when
> sat in a traffic jam for example, not constantly, just a few shudders
> every 10 seconds or so. I replaced the rubber engine mounts to see if
> they were to blame but it made no difference. The idle speed stays
> totally constant even when it shudders. With the engine running and
> the bonnet up, you can feel and see the shudder while at idle although
> you can't really hear it, no change of engine note or anything. Once
> driving the engine runs perfectly.

I'd try cleaning the idle control valve and checking the rotor arm /
distributor isn't worn out. I'd also check for air leaks in the intake
hoses.

--
Who needs a life when you've got Unix? :-)
Email: , John G.Burns B.Eng, Bonny Scotland
Web : http://www.unixnerd.demon.co.uk - The Ultimate BMW Homepage!
Need Sun or HP Unix kit? http://www.unixnerd.demon.co.uk/unix.html
www.Strathspey.co.uk - Quality Binoculars at a Sensible price

On May 16, 11:34 am, John Burns > wrote:
> > Hi all, I have just recently bought another E30, a 1991 325
> > convertible to replace the 320 i already have. The new car runs
> > perfectly when driven but at idle there's a bit of a shudder from the
> > engine every now and then. You can feel it shaking the car a bit when
> > sat in a traffic jam for example, not constantly, just a few shudders
> > every 10 seconds or so. I replaced the rubber engine mounts to see if
> > they were to blame but it made no difference. The idle speed stays
> > totally constant even when it shudders. With the engine running and
> > the bonnet up, you can feel and see the shudder while at idle although
> > you can't really hear it, no change of engine note or anything. Once
> > driving the engine runs perfectly.
>
> I'd try cleaning the idle control valve and checking the rotor arm /
> distributor isn't worn out. I'd also check for air leaks in the intake
> hoses.
>

Thanks John, I might try spraying some carb cleaner around the hoses
then. The main intake boot that normally fails on these seems to be
quite new looking at it, so I suspect that's been replaced recently
already. Good idea on the distributor too, hadn't thought of that,
although you'd think that it would cause problems at higher revs too
wouldn't it?

> already. Good idea on the distributor too, hadn't thought of that,
> although you'd think that it would cause problems at higher revs too
> wouldn't it?

Maybe it is. It'll wear gradually so all you'll notice is a slow decline
in high end power and fuel economy.

--
Who needs a life when you've got Unix? :-)
Email: , John G.Burns B.Eng, Bonny Scotland
Web : http://www.unixnerd.demon.co.uk - The Ultimate BMW Homepage!
Need Sun or HP Unix kit? http://www.unixnerd.demon.co.uk/unix.html
www.Strathspey.co.uk - Quality Binoculars at a Sensible price

In article
>,
MarkS > wrote:
> Hi all, I have just recently bought another E30, a 1991 325
> convertible to replace the 320 i already have. The new car runs
> perfectly when driven but at idle there's a bit of a shudder from the
> engine every now and then. You can feel it shaking the car a bit when
> sat in a traffic jam for example, not constantly, just a few shudders
> every 10 seconds or so. I replaced the rubber engine mounts to see if
> they were to blame but it made no difference. The idle speed stays
> totally constant even when it shudders. With the engine running and
> the bonnet up, you can feel and see the shudder while at idle although
> you can't really hear it, no change of engine note or anything. Once
> driving the engine runs perfectly.

Idle misfire is often down to a poor spark - for whatever reason. The
mixture is at its weakest and that needs the best spark. Check the usual
things - especially plug leads.

--
*Is it true that cannibals don't eat clowns because they taste funny?

Dave Plowman London SW
To e-mail, change noise into sound.

On May 16, 3:56 pm, "Dave Plowman (News)" >
wrote:
> In article
> >,
> MarkS > wrote:
>
> > Hi all, I have just recently bought another E30, a 1991 325
> > convertible to replace the 320 i already have. The new car runs
> > perfectly when driven but at idle there's a bit of a shudder from the
> > engine every now and then. You can feel it shaking the car a bit when
> > sat in a traffic jam for example, not constantly, just a few shudders
> > every 10 seconds or so. I replaced the rubber engine mounts to see if
> > they were to blame but it made no difference. The idle speed stays
> > totally constant even when it shudders. With the engine running and
> > the bonnet up, you can feel and see the shudder while at idle although
> > you can't really hear it, no change of engine note or anything. Once
> > driving the engine runs perfectly.
>
> Idle misfire is often down to a poor spark - for whatever reason. The
> mixture is at its weakest and that needs the best spark. Check the usual
> things - especially plug leads.

Right, thanks. Tonight I had a quick look and have more or less
discounted a vacuum leak (spraying carb cleaner around didn't have any
affect and all the hoses look good) so I think it's definitely
ignition. I have also noticed another symptom which I'm hoping will be
part of the same problem: with the engine at idle (hot or cold), if I
blip the throttle on and off quickly (most noticeable if done by hand
under the bonnet) there's a definite hestitation/flatspot before the
engine revs freely. In fact if you watch the needle the revs seem to
even drop a fraction before it picks up. To eliminate the plugs
themselves I replaced them with a newer set from my 320 and this made
no difference so I'm thinking about swapping the distributor cap,
rotor and ht leads next. Does that sound sensible for the symptoms?
Thanks again

Rev it to 3000 rpm and then light your foot off totally. If it dips
below idle and almost stalls that's a sign of a vacuum leak.

> Right, thanks. Tonight I had a quick look and have more or less
> discounted a vacuum leak (spraying carb cleaner around didn't have any
> affect and all the hoses look good) so I think it's definitely
> ignition. I have also noticed another symptom which I'm hoping will be
> part of the same problem: with the engine at idle (hot or cold), if I
> blip the throttle on and off quickly (most noticeable if done by hand
> under the bonnet) there's a definite hestitation/flatspot before the
> engine revs freely. In fact if you watch the needle the revs seem to
> even drop a fraction before it picks up. To eliminate the plugs
> themselves I replaced them with a newer set from my 320 and this made
> no difference so I'm thinking about swapping the distributor cap,
> rotor and ht leads next. Does that sound sensible for the symptoms?
> Thanks again

--
Who needs a life when you've got Unix? :-)
Email: , John G.Burns B.Eng, Bonny Scotland
Web : http://www.unixnerd.demon.co.uk - The Ultimate BMW Homepage!
Need Sun or HP Unix kit? http://www.unixnerd.demon.co.uk/unix.html
www.Strathspey.co.uk - Quality Binoculars at a Sensible price

>> discounted a vacuum leak (spraying carb cleaner around didn't have any
>> affect and all the hoses look good) so I think it's definitely
>> ignition.

Never, never discount a vacuum leak. Go ahead and check the ignition but
realize that there are many subtle ways for vacuum leaks to occur that are
pretty damn hard to detect. Not as bad as with a carb, though, thankfully.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Hi John, dropping down from 3000 to idle is fine, it doesn't dip
below. Thanks.

On May 20, 5:03 pm, John Burns > wrote:
> Rev it to 3000 rpm and then light your foot off totally. If it dips
> below idle and almost stalls that's a sign of a vacuum leak.
>
> > Right, thanks. Tonight I had a quick look and have more or less
> > discounted a vacuum leak (spraying carb cleaner around didn't have any
> > affect and all the hoses look good) so I think it's definitely
> > ignition. I have also noticed another symptom which I'm hoping will be
> > part of the same problem: with the engine at idle (hot or cold), if I
> > blip the throttle on and off quickly (most noticeable if done by hand
> > under the bonnet) there's a definite hestitation/flatspot before the
> > engine revs freely. In fact if you watch the needle the revs seem to
> > even drop a fraction before it picks up. To eliminate the plugs
> > themselves I replaced them with a newer set from my 320 and this made
> > no difference so I'm thinking about swapping the distributor cap,
> > rotor and ht leads next. Does that sound sensible for the symptoms?
> > Thanks again