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[X30XE]

A classic case of "did you **** with it??" "Yes" "Well aren't you a silly bar steward"...

- All 4 plugs taking oil swimming lessons - drained, carb cleaned and refitted
- Throttle removed and cleaned
- IACV thoroughly flushed out (all galleries)
- Throttle butterfly adjusted so closed completely
- vacuum to rocker case line cleared
- breather to intake hose clear
- crankcase breather clear


...managing to rev itself between 800 - 1.6k rpm on a 1-2 second cycle even with IACV unplugged. 


Any suggestions please?   Other than pushing it into a reservoir...

[zirk]

Sounds like left over Crab Cleaner, especially in the ICV, take it out it for a long hard Italian Tune Up, will probably go back to normal over a short time. 

[X30XE]

Hmm. Tried that. Trouble is the IACV is closed when you hoof it 

Is code 0340 always present with the engine off or is that foobarred?

[Nick W]

You must have an air leak for it to rev like that with the IACV disconnected and the throttle body adjusted shut. Out of curiosity, why did you do that?

You need to check that anything you have, or might have, disturbed is undamaged and properly fitted.

[X30XE]

You must have an air leak for it to rev like that with the IACV disconnected and the throttle body adjusted shut. Out of curiosity, why did you do that?

You need to check that anything you have, or might have, disturbed is undamaged and properly fitted.

Yes, clearly, but why isn't it just idling high if there's a leak? Don't get why it's hunting if it can't attempt to regulate airflow 

 I adjusted the end stop to let the throttle plate shut as advised on the "how to clean your throttle body" threads.

Seems to only do it when warm.. Closed loop fuelling getting confused by leaky exhaust? something to do with dodgy cam sensor?

[Nick W]

Does Motronic adjust fuelling and ignition as well as the IACV to achieve the target idle speed? Doing that without accurate control over the airintake could cause all sorts of odd symptoms.

[zirk]

Could be air leak, but if its hunting might be ECU didn't like the changes and is still relearning. 

You could try diss'ing the ECU for a while, out of interest how does it idle when you put the steering on full lock when stationary.

[RobG]

Hmm. Tried that. Trouble is the IACV is closed when you hoof it 

Is code 0340 always present with the engine off or is that foobarred?

Nope, cam sensor knackered

[TheBoy]

Hunting is a classic sign of air leak.

The cam sensor is buggered, but that's an unrelated fault.

[minifreek]

Sounds more like a knackered ICV to me as I had the same symptoms on my Vec 2 litre....

Changed for a new - not cleaned out - ICV and it cured it immediately...

[X30XE]

Right well the cam sensor can go on the ignore pile then.

Further experimentation shows that :

- misting crab cleaner around the throttle housing/iacv has no effect on idle speed, so unlikely to be an air leak to outside
- placing a large screwdriver on the body of the iacv whilst the fault is occuring and clonking it with a birmingham screwdriver yeilds an almost stall followed by rattley-hell-death noises followed by a stutter-y return to idling

Conclusion : Either the iacv is toast or something proximate to it does not enjoy the birmingham school of mechanics treatment.

Plan A : dismantle and inspect iacv with a view to repair
Plan B : blank the little sh.. off and bodge the throttle end stop 

[X30XE]

Follow up :

Dismantling wasn't viable - brass bit wouldn't come out. Gave up. 

 Blanked it off completely and adjusted throttle end stop.  No longer hunts and throttle response seems much improved.  ~1krpm idle speed isn't ideal, but it's better than the embarrassment of sitting at the traffic lights with it impatiently revving itself like a tw*t 

Not a long term solution, but when you only pay £200 for a car that doesn't come into it 

[minifreek]

You can't clean the ICV to fix it, it needs replaceing...

For £25 new, its worth replaceing regardless of how much the car cost to buy....

[terry paget]

Sorry if already mentioned, but have you cleared the small breather hole, and have you replaced the cam cover gasket? Clearly cam cover gasket has been leaking, which means an air leak into induction tract, which will affect idle.