25mpg on a run for a 16v

[Rich16v]

This can't be right, l did 270 miles in four hours and used a full tank full. The car was running like a pig before l changed relays numbered 167 & 30 but now l only get between 20 and 25 mpg also the revs take a long time to settle to idle and if you hold it at say 1500 revs it will drop and then rise constantly. also while l'm here the little thin vacuum that comes from the throttle body to the air box, does it go on the top or bottom fitting, one is plastic and the other is metal, this is on a 2.0 16v. by the way l've cleaned out the tb & isv and changed all the vacuum hoeses. l think it could be time to take it to vw 

Cheers
Rich

[Overseer]

nah that aint right..  if i run about 20 miles up the motorway sticking to the speed limit carefully i can get mid to late 30s MPG.

does sound like you have problems similar to what i've had until recently.

how far down to your rev's drop if u sit at idle for say a minute?

i'm not sure about the connection you mentioned.. i'll have to have a look.

in the mean time... 2 things to check...

1) check the connection from the manifold that comes out just under the ISV goes into the little box over on the left of it (crankcase breather thingy)

2) check the other main vacuum hoses for leaks.. one i overlooked which seems to have solved my problems was the one that comes out of the block itself directly under the where coolant comes of the block into the top of the radiator

[Rich16v]

l don't know if l've checked the one from the block or not l'll have a look later, as for the revs they drop to about 900-950 given time.

[Overseer]

ok.. well the 'time' thing.. is partly due to the way the car drops to idle.. theres a fast mode (if u rev it stays high..) then if its really idle for 30 seconds or so it drops to low...

with a vacuum leak present it doesnt drop.. sometimes..

try to be as thorough as you can checking the hoses for splits etc..

[Rich16v]

This hose that comes off the block is it the big one that goes to the crankcase breather thingy

Cheers
Rich

[Overseer]

yeah i think thats where it goes..  mine had a huge split along the top edge..it gets quite hot so i figure that affected it..

there is also that smaller connection i mentioned from the manifold under the ISV that _also_ goes there..



when i got my car someone had put a screw in the tube that comes out from under the ISV just tying it off.. and had left the crankcase connection open ... eek..!

[Rich16v]

yeah l looked at some of the old posts and see that 
l've changed the smaller pipe, l've got the breather thing and all hoses in my kitchen now and looking at em all, the one off the block has a lot of crap in it and l'll give the isv another clean for good luck to while its off.

[Overseer]

in your kitchen?! lol

i just picked my car up (see "my exhaust fell off" LOL) and took it for a run along the motorway before coming back to work. got on the motorway in the middle lane.. and was doing 25 mpg.. got up to 80mph and sat at that speed in 5th.. very quickly the mpg started to rise... by the time i'd covered the distance to between junctions 26 and 25 of the M5...   (wellington -> taunton) which is about 10 miles or so... the mpg was at 30 mpg.. and still rising

[Rich16v]

l also went for a run on the motoway was getting 34mpg below 3k at 80 it was at 30 till l went up a big hill and dropped to 28 and then wouldn't go over 29ish mpg

[Rich16v]

l've had enough of it now so 29ish l can live with and the idle isn't to bad, l'll see how it goes now l've switched the pipes round again on the air box.l'm going to block the isv off and see what that does just in case it is leaking.if you take your the throttle some times it holds back and some times it don't.