Judder at 30mph/1500rpm

[simdel1]

Hi guys,

I've been noticing a strange trait with my new car lately. If I drive at 30mph (indicated) in 4th (about 1500rpm I think), the engine seems very prone to shuddering, almost as if it's trying to stall. If I change to 3rd, the problem goes away, but obviously I'm burning a lot more fuel!

I have a couple of ideas about this.

First, I think my speedo is massively out (it bounces like a rabbit on speed below 30mph) so maybe 30mph indicated is actually 25rpm...which would explain why it's not so happy. I did a bit of a fag-packet calculation and estimated that I need to be at 1800rpm in 4th to be doing 31mph. If I do run at 1800rpm (38ish indicated) the shudder is less noticible, but it's very sensitive to throttle movement and can still shudder a bit if i'm not concentrating. Could this have anything to do with the fast-response cam thingy on the throttle?

Second, I haven't had chance to do plugs/oil/filters yet so I'm hoping that some of the lumpiness is just a symptom of some worn service parts. While I'm on that subject, the air filter looks to be one of those fancy washable things that you get with aftermarket induction kits. What's the correct method to wash those types of filters?

Thirdy, the engine mounts are knackered. I'm planning to replace them with the £40 jobbies from type911. Could the mounts be contributing to the engine's inability to be stable at low revs whilst driving?

 

[rav]

I have a similar issue with my car, but always put it down to being in too tall a gear at too low rpms.
If i experience the shudder, i just change down a gear. I put it down to driving a diesel on a daily basis and hence have been spoilt with lots of low down torque.

I would be interested to see what others suggest.....

 

[Northern924]

Car was not designed to do 1500rpm in 4th!! Its a sports car and isn't geared to be driven like that, the mrs drives a 4x4 (valid reason - can't pull a twin axle horse box with a petrol vectra!!!) but she always tries to do the same.

As you can guess I'm with Rav 100%, don't drive a coupe sports car like a diesel or petrol eurobox, its not what it was designed for and please don't take this the wrong way Simon but if you're worried about burning a few extra mpg you've bought the wrong car [8D]

 

[simdel1]

No offence taken! I was just checking that everything was ok really and that my car wasn't unusual. I think the fact that I drive a very torquey diesel saloon as my daily driver has spoiled me too. As long as I know to keep the revs above 2000rpm for smooth progress I'm happy!

I'm not that bothered about fuel economy. It's offset by the 50mpg of the Rover anyway! Carbon offsetting is the future []

 

[Lowtimer]

I don't really like to run mine under any sort of load below 2000 rpm. I consider 2000 to 3000 as the bottom end, 3000 to 4500 as the mid-range, and anything over 4500 as top end. That said, it should not judder badly at 1500 rpm at light throttle setting. If your engine mounts are known to be dodgy, and it definitely needs a service, I bet those jobs will greatly improve it.

 

[Mike_Pollock]

Do the leads, plugs, dizzy, arm, and mounts and it will feel so much better! - wont cure it completely at those revs/mph though

 

[Frenchy]

You are putting a load of strain on your crank driving like that................NOT GOOD !
Under revving like that is more damaging than over revving, buy a Micra if you are looking for fuel consumption []

 

[Northern924]

Hey Frenchy that was harsh lol

But to be honest I rarely like to run much under 3k, at that point you are in the 'power band', much more fun []

 

[bmnelsc]

IIRC I read (perhaps in the owners manual for my '91 S2) that minimum RPM was 1700. This works under light throttle conditions even in 2nd (when you really don't want to drop to 1st - coasting up on traffic when the light has just gone green, etc). I'd avoid the 1500 RPM guide also as per previous comments - lugging the engine leads to smeared bearings and other woes.

 

[simdel1]

Ok, cool. So more revs and service everything. []

I appreciate that I'm going to be asking a lot of stupid questions ( as clearly this one was!) The problem is that my entire car history consists of my beater Ford Fiesta (which I still own) and my diesel Rover 75 (which is the daily driver). Having never really driven anything with a performance orientation before I'm having to learn not to drive it like my other cars.

The fuel comment was more about making sure I wasn't throwing good fuel away during the boring 30mph bits that could be put to good use on some twisty derestricted bits. []

Please, no more suggestions of Micras and the like...I already have one shopping trolley, I don't need another[]

 

[david924s]

I usually drive my S2 in fourth around the estate I live on which is normally around 25-30mph and it seems to be fine at these speeds with no juddering and can still pull if needed. indeed I normally get through the gears fairly quickly with an aim to get into top as soon as practical without over reving it, I realise this is probably not how to drive a (so called) sports car but it is how I have always driven and only hang onto every gear throughout the rev range if I am really pressing on which is not so often. I find the car still keeps up with traffic and operating speeds without the need for reving the engine, never thought about it damaging the engine I was always more aware of over revving doing this than under revving.

 

[vitesse]

Both of our 924S's will drive in 5th at 30 mph & cleanly accelerate away from that speed in dawdling traffic-can't see that you can damage a crank rotating at around 1000revs anymore than leaving an engine idling-as soon as you feel the engine start to judder,just change down-just because they are sports cars doesn't mean they can't be docile in traffic.[8|]

 

[peanut]

I agree with David and Vitesse. Cruising at 1500rpm is very unlikely to damage a 944S2 engine . The car is designed to be a grand tourer not a sports car in the general sense of the word. It isn't an MX5 .

I certainly wouldn't cruise through a 30mph zone at 3000+ rpm in first or second gear [] far to wearing on my nerves and hearing .
I suppose when i was 17 I used to drive everything at max revs ,like I stole it []