When driving in hard to work this morning I noticed the idle revs were really high. about 2k then the check engine light came on and it dropped really low 300. Afterdriving very carefully the rest of the way to work I opened the bonnet and noticed on of the rubber hoses had came off the cylindrical plastic thing in the front left of the engine compartment. The particular hose is the fist one from the left that connects to the air filter pipe. Pushed it back on now all seems ok. What is this and have I done any permenent damage ?

 

Its not your fuel pump thats for certain. Cant remember what it is though?

I have done this a few times when i have forgot to plug it back in after changing/cleaning air filter etc. Did me no harm.

 

IIRC that's the carbon cannister used to "remove" fuel vapour. If you don't fit the hose the car will pick up unmeatered air as the connection is past the MAF, hence the dodgy idling.