RPM's rise when clutch is disengaged, why?

[Deadly BlaZe]

Everytime i step on the clutch to change gears, my rpm's rise by about 400 every time. Why does this happen?

 

[jumpfroggy]

I don't want to be an idiot, but I know I do this sometimes...

Could it be just that you're not taking your foot off the gas pedal early enough before you hit the clutch? If you kept your foot on the gas pedal without moving and pushed the clutch, your RPM's would skyrocket (since now the engine is without load... did it to rev on my friend just tonight, actually). If you do both at the same time, there may be a moment when the engine is still getting the same amount of gas while the clutch is suddenly released, creating the same situation for a split second. So that may be why the RPM's jump up just a bit, then start to go back down.

If it's something else, please elaborate. I've been driving automatic's till I got my TSI (bleh), so now I'm paying close attention to the details of clutch, turbo, launching, flywheels, etc. It's all very interesting.

Again, I do not mean to insult with a simple answer. Just curious if that could be it.

 

[Mitsubishified]

Well sir im not completely sure about his however; I believe the reason your engine rpm's rise when you engage the clutch is so the engine won't stall out. Think about it if the engine is at the same rpm that it engages at then that means you would have to accelerate (or push on the gas pedal) so it wouldn't stall out. I think the reasonalbly easiest answer is that its normal because if the rpm's didn't rise then the car would sputter and die. Now don't quote me on this but im pretty sure thats what happens. Now if your rpm's rose then fell off and on while the clutch was engaged then i would say you have an idle sensor problem. I think thats enough rambling from me tonight. Hope this helped on some level man,
Luke

 

[carl5463729]

I'm pretty sure jumpfroggy is right. to make it easier it is because when you step on the clutch you are letting all of the load off of your engine and tranny, therefore if you have your foot in the same spot on the gas, when the clutch is down thier is less load and it spins easier. if the car is in gear, it has more load and won't be at a higher rpm. I usually let off of the gas right before i shift, then it is not as noticable.

 

[Deadly BlaZe]

Thanks for the answers guys, but they're all wrong. At first I thought it was exactly what jumpfroggy said..so I let off the gas completely while still in gear and THEN i pushed the clutch; the rpm's jumped up again. I've never had this problem in my other two 5 speed cars.

 

[jumpfroggy]

Yeah, that is something different. Normally if you let off the gas you should be engine braking, and if you release the clutch it should immediately start going back down. The second obvious thing would be if you're cruising below idle speed. Normal idle (for me, anyway) is around 700-800. So if I slow down till about 500 (and the engine starts to stall a little), then release, it should pop back up to idle or a bit past it. This may also happen if your idle speed was set high (if your idle was 1500 and you were disengaging clutch at 1200, there's your 300 rpm).

I have a hunch this is not your problem either. Sounds like your engine is being a bit runaway on you. So right now you are cruising along, then you take your foot off the gas, wait a second, then push in the clutch pedal and the rpm's increase by 400. When the engine pops up 400 rpm, does it then slowly settle back down? What rpm are you doing this whole thing at? Does it happen more with higher or lower rpm's? Is there a certain speed it always pops up to?

Try to describe how the engine acts, before and after the clutch. My guess right now is that there's something happening where the engine will still be receiving some juice after you let go of the gas, so when you push the clutch it's as if you still have your foot on the gas lightly for a split second, then it goes back down. I've no clue why that would happen and what would cause it, it's just a wild guess. Anyone see this before?