This is weird!!!!!

The_Economist

Has any body had or got this problem with there car. A friend has got a 1.8turbo 20v petrol Voltswagon Passat on a X plate. When it is on idle speed and you turn on the heater the revs start to go up and down, turn of heater fan revs settle down and go back to normal idle speed. Its been back to dealer and they dont know what is wrong with it and want to charge mega bucks an hour to look at it further.:mad:
Can anyone help please!!!!

thescouselander

When you say the revs go up and down - exactly by how much do they go up and down?

The_Economist

thescouselander wrote: »

When you say the revs go up and down - exactly by how much do they go up and down?

Erm, very noticeable buy the sound of it. Ok erm sounds like if you breath in and out hard very fast! Idles normaly at around 900RPM but with the problem goes up and down.

harveybobbles

Its b'cos when you turn things on in a car, it uses a bit more of the battery.
Its using a bit more battery/engine power to run the fan, which causes the engine to drop, but the anti stall device ups the engines output. Hence why you get a surging sensation...

It's like in your house you notice lights flicker if you put lots of things on etc...

Nowt to worry about.

The_Economist

harveybobbles wrote: »

Its b'cos when you turn things on in a car, it uses a bit more of the battery.
Its using a bit more battery/engine power to run the fan, which causes the engine to drop, but the anti stall device ups the engines output. Hence why you get a surging sensation...

It's like in your house you notice lights flicker if you put lots of things on etc...

Nowt to worry about.

Thanks harveybobbles, i can see where you are coming from but unfortunatley i will have too disagree with you on this one. The amount of surging doesn't justify the amount of energy needed to run the heater fan.

harveybobbles

Maybe go check the alternator is pulling enough charge.
Throttle pot might be clogged up with dirt and other bits of rubbish too...

The_Economist

harveybobbles wrote: »

Maybe go check the alternator is pulling enough charge.
Throttle pot might be clogged up with dirt and other bits of rubbish too...

How do i/we check the throttle pot?

harveybobbles

Undo it, dear Lizer, dear Lizer. Undo it dear Lizer my friend!
Then look at it dear Lizer, dear Lizer. Look at it dear Lizer, my friend.

Wipe round it with a cloth, removing all buits of oil and crappy deposits.

ollyk

take to a battery supplier and get them to check the alternator and battery, which they should do for free!

The_Economist

ollyk wrote: »

take to a battery supplier and get them to check the alternator and battery, which they should do for free!

Thanks ollyk. Cars carn't live with them carn't live without them.

Stephen_Leak

Idle speed is usually controlled by the idle control valve (which can get clogged up) and a maze of vacuum pipes all around the engine (the rubber bits of which split and therefore leak). However, some heaters also use this vacuum to activate the control gates. Could a vacuum leak here be the culprit?