Idles revs rise whenever any electrical load applied?

I must admit, I haven't investigated the problem myself yet, but I'm after any advice or previous experience. The problem is that, although the car idles OK with minimal electrical loads, as soon a a load such as headlights or climate control is turned on, the idle revs rise. Even turning an indicator on makes the revs rise when the indicators are illuminated, and lower when they turn off. That's a pretty small load! For example, the car will idle OK at or below 900 rpm, but when the headlights are turned on, it will idle at closer to 1800 RPM. The battery earth cable is OK, but I haven't checked the engine earth yet. The battery condition is reasonable, but not perfect. The car is a TT manual. If I find anything, I'll post it on this thread. Hopefully I can do a bit of research tomorrow. In the mean time, if you've got any useful tips, fire away!

 

Make sure that the IACV hose does not have a split in it.

 

alternator good?? i know when my excel's alternator was on its wayout it did the same thing

 

I don't suspect that the IACV is a direct cause, as the car idles at more or less normal revs when there is minimal electrical load. Alternator seems fine - charging voltage is good, and comes in at low revs.

 

Dnagerous, its your battery. It has lost its voltage. I think you will find that when the car is shutdown that the voltage will be below 12 volts indicating a failed, or partially failed cell.
Swap it out witha known good battery before buying a new one, to prove it is the fault though.

 

It might be the battery - I've already decided to get another one on Monday in any case. I have checked it though, and it holds charge, static voltage doesn't indicate a dud cell, and it has around half of its CCA capacity left - not good, but shouldn't affect operation while the engine is running - at least not the symptoms I'm seeing. I'm leaning more towards maybe a dud engine/chassis earth, but I haven't checked it yet. Too wet yesterday, and a long list of thing to do - some of them even Zed related

I have had a dud battery in my other Zed a few years ago, and boy was it a pig to drive! Started OK, but ran like crap.

Cheers,

 

Update

Not the battery. I've just fitted a newish (unused, been on a trickle charger since it was bought) Exide X56. Same problem. Battery to chassis and to engine block earths look fine too.

Interestingly, it appears to be very load related. Brake lights on, revs raise by around 100 rpm, and then most of the time it will settle back to idle after around 20 seconds. Headlights on, revs raise by around 500 rpm and stay high.

 

aint that normal? i have a safc so i can check the rpm pretty precisely, rpm goes up when electrical accessories/light are on.

 

The job of the IACV is to do excactly this but his is excessive.

 

if theres a split in the IAC hose, could this result in lack of engine power if any? probably a stupid q, but i am wondering

 

It 'can' result in poor running.

OP, I would probably unplug the IACV and see if the idle falls back to a normal level.

I am still basically a learner when it comes to VG30 technical so if I give incorrect info then please let me know.

 

It not your battery check the alternaotr voltage when you swtich lights on and off and idle (ie the thijngs that make the engine revs jump). If so it could be the alternator itself, or something as simple as a loose belt.

 

Alternator is fine, charging voltage is fine even under headlight load, belts are fine.

Come to think of it, it wouldn't be alternator or belts, as the problem is immediate, not delayed.

 

I still believe that it is due to accessory idle up.

 

TeeJay, I am aware that the Z32 increases idles when the A/C is on, and also it gives a slight rev 'blip' when changing gears in a manual, but I am not aware that it raises revs in any other situation (apart from when it's started cold).

Are you aware of any other situation where it raises idle?

 

The only other one I can think of is the engine temp. the signal from the ecu changes timing. Other than that I think I'd have to run a bit of a diagnostic./

 

coolant temp reads fine via Conzult, no error codes, and wiggling the coolant sensor cabe does not result in coolant fan coming on as it would if the contact was intermittent.

I haven't chased up this issue any further to date, apart from checking that the alternator and charging is OK, ConZult reports no errors, changing battery and checking earths, as I've been concentrating on the 'defectable' stuff first. I'll get to it, but in the mean time, keep throwing ideas