revs drop between changes

M

mad4slalom

Senior member
z4mc just been reading posts about slight hesitation from idle, have had mine a month and am gradually working thruogh varios issues that frustrate me about the car, done clutch stop and cdv, g.box and dif fluid changes, all big improvements. this hesitation at idle , is definately present, it does'nt bother me much, but what i have always thought is that for a really sporty drivers car, when i downshift and i try to rev match, the revs drop way more than i feel they should,and when you blip the throttle it seems very sluggish to rev up, tried the throttle / key reset but it was'nt that, previous post mentions positive results from tps replacement, any others with same rev drop symptoms and suggested cures, all part of enthusiast car ownership i know, and v satisfying when we find a cure for these little niggles, and just shows how great this forum is to be able to share ideas and opinions with so many others. :thumbsup:
 
just had another thought that this rev drop thing could also be contributing to making gearchanges not very smooth as by the time your foot is back off the clutch, the revs have dropped more than they normally would have, seems to make sense to me, any thoughts, i'm on a mission now as are many others i'm sure.
 
The symptoms your describing are not the same as everyone else is having.
Most are having a slight hesitation at standstill when you blip the throttle which doesn't affect the drivability.
 
From datalogging of the ECU, when you lift-off, fuelling is cut to that required for tick-over, only, therefore the revs can only drop at a rate commensurate with the slowing of all the engine parts, including the flywheel, when the engine is disconnected from the drive train when the clutch is depressed. Obviously, the longer the time the drive train is disengaged, the greater the time for the engine revs to fall. Is the problem that you're reporting not all part and parcel of the overall problem that you've been having with gearshifting?
 
If you put in in sport mode you'll see the throttle pedal gives you a much better 'blip' with much less input.

I find in normal mode the throttle pedal doesn't respond quick enough for blipping.

Suppose that's what we get for having a drive-by-wire throttle :headbang:
 
you say its not related to drivability, ok, but the fact that there is a little hesitation from idle has much less impact on driveability i feel , than the droppin revs thing,because in real world driving situations when do we need to mash the throttle from absolute idle ? we are normally moving already so the revs are already way above idle. the rev drop thing , or lets not call it that as you gave a technically excellent explanation of what is happening, lets call it a sluggish pick up, as a layman, i dont know if this is in fact normal, or is it a problem, i just picked up on other posts that mentioned this too and recognized it in my car, have others experienced the same and would tps change help. thanks.
 
Send me a PM of your whereabouts and if you're near enough, I'll hook it up to my datalogger for you and we can see what's happening.
 
no, i move antiques and pianos around the country so i do get up your way, trouble is its a nightmare trying to fit a 7' 6" steinway in a coupe, so I'd be in the van ! generous offer tho, thanks :thumbsup:
 
I replaced both my TPS's as the car revved like a pig, coughing and spluttering when revved, while I was there I cleaned out all the throttle bodies and also the ICV, the car now runs so much smoother although there is still a very slight 'fluff' if I really stab the throttle at idle..although I am VERY fussy with these kind of things

Like you the revs still drop quickly but I think that maybe the way the engine is designed and just needs getting used to. If you have the bonnet open while revving the car you can see the butterflies opening and when you take your foot off the pedal they snap shut (goes with what exdos said about the fueling)..on most fly-by-wire cars the throttle is designed to shut the butterflies slowly so the car is smoother.

I used to have a 350z and that took an age for the revs to drop after you revved it.
 
Here's a graph from my datalogging which illustrates the point. As soon as the throttle pedal is released during gear changes, the fuelling is cut right back to an Air/fuel ratio of 25:1 or more from the stoichiometric levels under throttle. The throttle bodies have snapped shut when this happens.


Z4MCAFRvRPMinacceleration-1.jpg
 
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