Revs rise slightly when changing up gear

[Dohey]

Hi guys,

Its only started today but ive noticed that when changing up gear the revs rise a little bit before dropping (and no im not keeping my foot on the accelorator lol). It seems to have more effect if im foot down and higher up in the rev range. It doesnt do it consistantly but its more often than it is not.

Any ideas on what it might be?

Driving a 1990 318is

Cheers in advance

Rich

[e30-EVN]

Afaik its supposed to do that anyway, the revs raise slightly for smoother gear changes.

Some1 correct me if I'm wrong of course, if I am

[Dohey]

Afaik its supposed to do that anyway, the revs raise slightly for smoother gear changes.

I dont know about that to be honest mate. Ive had the car for 6 months now and its never done it before. Also raising the revs whilst doing a down shift would make sense but not on an up shift I dont think.

Cheers for the idea though.

[e30-EVN]

It aint an "idea" mate! I've driven plenty of cars that do it, my mates m42 e36 used to do it aswel. I will admit strange it hasn't done it for 6 mnths mind

[johnl320]

If your IS is anything like mine then you need to start by looking at air leaks, I found that I had splits in pretty much all the air pipes around the inlet manifold. To check these let the engine tick over and spray the black hoses around the inlet manifold area with WD40
while doing this listen for a change in the revs, if you hear a changes then you've found an air leak.
I'm not saying this is the fault but its a good place to start. There are plenty of air hoses on the M42 lump that can leak air in and effect running.

[Dohey]

Thats a good tip, ive not heard that before, cheers John. My initial thought was a sticky throttle maybe. I know the M42 has a 'two stage' throttle body and thought maybe it had something to do with the cross over from the larger plate to the smaller plate. Ill give your idea a go though John. Cheers

[e30BMart]

It aint an "idea" mate! I've driven plenty of cars that do it, my mates m42 e36 used to do it aswel. I will admit strange it hasn't done it for 6 mnths mind

It wouldn't raise the revs if you go to a higher gear that would be dumb...

[e30-EVN]

And how would that be dumb??! New cars hold when you change gear to make smoother changes...

[e30BMart]

And how would that be dumb??! New cars hold when you change gear to make smoother changes...

Some cars like the new 370z revmatch when you go to a lower gear (making revs go up while the clutch is engaged) so that your revs are matched (hens the name) to the road speed and in such making for a smoother shift.

On the other hand if your going from 3rd to 4th (ie) and your revs go up when you engage the clutch then its kinda not rev matching is it? After your revs go up and you bring the clutch back your engine is gonna match your revs to road speed anyway (the value of which will be lower than when you pressed the clutch in) so the further you are from road speed/rev speed balance the jerkier the ride is going to feel...

Perhaps for under 3k revs holding might make for a smoother shift due to the lower RPM differences I can't confirm at this moment though.