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[sooty]

Just had an MOT refusal because the idle was too fast for the MOT emission test. 900+ rpm and the test needs 520-780 rpm. The mechanic said I should take it to a main VX dealer to get the ECU diagnosed. Lots of £ signs flashing before my eyes!

It seems so trivial to fail on something like that but there's nothing in the Haynes manual to suggest that the idle speed is adjustable.

I changed the Idle Control Valve fairly recently (because of an erratic idle) and it's been fine since then so I'd be surprised if that's the problem.

Generally, the car's running OK - apart from an oil leak that seems to be getting worse. Not sure it's connected to this problem but here's the detail: The engine was running lumpy, like it was missing. A Saab mechanic diagnosed a oil leak that was flooding the HT leads/spark plug pots. He fixed it by replacing the rocker box gaskets. All was well for a while (I do very little mileage) but now the oil leak is back with a vengeance and it's running lumpy again. Doesn't seem to get through much oil but a little goes a long way - as the MOT guy found out when he got dripped on with hot oil. Boy was he grumpy.

Anyway, back to the plot. Does anybody have any ideas how I can slow the idle down - even temporarily would do - so that I can get it through the MOT?

Thank you.

[Kevin Wood]

Firstly, the idle speed is probably down to an air leak somewhere, or the throttle stop has been adjusted incorrectly to mask the symptoms of another problem such as a failure of the idle control valve.

Throttle should close completely but not so completely that it sticks into its' bore.

You can try squashing the small rubber tube that feeds the idle valve by hand while it's idling. It should immediately stop. If not, an air leak is feeding it more air from elsewhere.

The cam cover gaskets fail and leak oil into the plug wells when the breather system blocks up. If the breathers were not cleaned when they were replaced, this probably explains why they have failed again so soon.

Have a look at the maintenance guides for more information on these issues, and welcome to the forum.

[cem_devecioglu]

your engine is getting extra air.. which means air leak somewhere else.. high likely from the plenum area..
 
you can spray some brake cleaners around engine to see if idle is effected..
 
personally I would check/change the 6 o-rings under the plenum.. 
 
ps: must type faster

[sooty]

Wow, thank you cem and Kevin for the speedy replies. Much appreciated - as is the info. I'll work through your suggestions in the morning (day off to get this sorted) and I'll let you know what I find, and hopefully what the resolution was.

With regard to the oil leak (and for others who might follow this thread), I think I've found the maintenance articles your referred to here:

Cleaning the V6 crankcase breather setup http://www.omegaowners.com/forum/index.php?topic=90653.0
V6 Plenum Removal http://www.omegaowners.com/forum/index.php?topic=90657.0

Is that correct?

[tigers_gonads]

Yup that's the ones 

As for the air leak, i'd check round the rubber gromit that seals the icv to the plenum 

[TheBoy]

As other say, airleaks are first port of call.

There is an adjustment in the ECU, but don't think its anywhere near that high. Once you've exhausted the possibilities of air leaks, throttle not closing and ICV problems, then we can look at ECU settings. Don't use Evans Halshaw at Crownhill, their service department is one of the worse I've ever had the displeasure to see.  We I'm back in the UK, I can always bring the Tech2 to work one day - Bletchley.

[MutantCav]

Normal idle on a 2.5 v6 is a steady 500 or 600 rpm depending upon whether you have aircon on or not so that is indeed what you are trying to achieve Check the air pipes for splits too, especially the 4 little ones where they attach to the back of the plenum

[sooty]

Must have been my lucky day! Manually pushing back on the throttle linkage (where the throttle/auto choke cables attach at the front of the engine) slowed her down to the right level. Bit of a clue that. Stupid not to check the obvious before panicking but I was spooked by what the MOT guy had said. The solution was easy...

There's a throttle stop screw with a 6mm locknut set just below the linkage. All it needed was a quarter-turn anti-clockwise to bring the rev level back into spec. The most difficult part was finding a 6mm spanner that would fit the locknut. A ring spanner is really needed but the nut was in just the right position to get enough purchase with a flat. Sorted. Whew!

Thanks for all your help - and especially to TheBoy for the offer of the Tech2 - thank goodness it wasn't needed on this occasion. It's nice to know that there are good people out there who are willing to help, even when they're on holiday!

Onwards and upwards. I'll get the MOT sorted tomorrow (at a different garage) and then it's on to the oil leak. I should start a new topic for that, right?

[Andy H]

Is the car new to you?

I wonder if someone has previously disguised a problem with the IACV by fiddling with the throttle stop screw

The throttle stop should be set so that the throttles close fully but don't go any further. The throttle body is soft aluminium and the butterflies will chew chunks out of it if the stop is screwed out too far