Two Techie questions (Fast idle and STVA)

[Red ones]

Your starter for ten:

Could a really out of adjustment fast idle cause the Secondary Throttle Valve Actuator (STVA) to behave as though it has failed? My STVA reports that it has failed, but only ever as the fast idle SHOULD back off. BUT the fast idle is shot....


And you question for five:

According to the manual the fast idle is checked by taking voltage readings using needle probes. Does this literally mean sticking needles through insulation, as I see no other way in to get a reading? If so, where do I poke the needles in as I don't really want to damage the cable insulation.

[Bibio]

i think the fast idle is controlled by the thermostat sensor but i could be wrong.

when you probe cables you insert the probes in the back of the connector block and not in the cable.

[Red ones]

Just seems odd how the STVA fault occurs when the fast idle should be backing off, but of course the revs are stupidly low because the fast idle is shot.

Do the needles follow the cables into the block?

[Bibio]

so let me get this right. you start the bike cold and the fast idle kicks in then settles. once settled the bike ticks over at very low revs?

exactly what i said. you stick the needle probe of the meter in the back of the block, you know the part where the cable enters the connector. sometimes you take the connector apart and stick the probes on the terminals to check continuity/voltage.

[Red ones]

Start the bike and fast idle cuts in. 10 seconds later the revs drop to about 1000. As bike warms up the revs return to 1250. I'm happy to experiment and sort the fast idle once I'm satisfied how to check for the mythical 1.21V input to the STVA and then test ride.

I'm hoping my STVA isn't Fubar partly for cost and partly because have you tried checking the resistance across the thing? No sodding space to swing a cat in there!

[Bibio]

a few questions before i have to copy the OEM workshop manual.

have you balanced the throttle bodies?

does the bike cut out at lights or coming to a stop?

why do you think it's the STVA?


there is more to adjusting the STVA than just measuring voltages and you also require a vernier gauge as its quite a complicated procedure.

[Red ones]

Throttle bodies balanced last summer.
The engine doesn't cut out, but it throws up a fault code 'C28' which is a faulty STVA, however, I'm not convinced that it isn't linked to something else.

The prob turned up a couple of months ago and has been intermittent, but only ever appears just before the engine is fully warm. Given the wonderful memory of the ECU if it does occur, it never resets without turning the ignition off then restarting.

I thought I would clear all other problems on the way to sorting this issue, so I have sorted the TPS which hadn't been working below 6,000rpm (new TPS fitted) but eh fast idle which I have been living with is still miles out - it never works and allows the bike to tick over very slowly when cold.

Fast idle is a simple and cheap problem to rectify to rule out before I face the inevitable replacement of the whole assembly. Besides it needs sorting. I have done the bit with the vernier etc - that's all fine, I cant do the resistance measurement across the STVA while I have human sized hands and eyes that don't protrude on stalks unlike the person who wrote the workshop manual.

[Bibio]

as far as i know the bike wont throw a code if the unit is mall adjusted it will however throw one if the wiring is dodgy. according to the workshop manual it throws the code if the ECM gets no signal to/from the STVA.

was the bike fine before you changed the TPS sensor (apart from the TPS being goosed)?

have you recently changed or unplugged the ECM (bike brains)?

[Sid Squid]

Does the STV wiggle about when you lift the engine speed? Use the Mark One Eyeball Method to check - take the airbox off and run the engine; do the secondary butterflies move something like they should?

If yes, and a fault with the STV isn't obvious, (despite the error code), set the fast idle when the engine is stone cold, at least do it when the gauge shows -- not a figure).
When the fast idle cam on the STV wears the initial start up speed is often fine, but the idle drops out before the motor warms. The fast idle screw will need only a teeny tweak to make a noticable change.

[Red ones]

Cheers Sid
You're spot on with the description. I'll prod the fast idle when the bike is cold which isn't often at the moment

I'll also check the wires again in case I damaged one changing the clutch cable.