Rough idle, fine rest of the time

[kevpuk]

My 54-plate Aero has developed a rough, stuttery idle in the last day or so. Absolutely no issues over approx. 1000rpm, or under load etc. Just at tickover.
With previous cars, this was likely down to Idle Control Valve or similar, and - on my Omega - involved a squirt of Wyns or similar and all was well.....

Quick update : This morning, after a 13 mile drive, the idle was nice and smooth.......stopped at some lights on the return journey, however, and the revs 'stuck' at around 1100rpm - revving the engine a little and letting it drop made no difference......next set of lights, back to slightly lumpy again

....the plot thickens.......

Does the 9-5 have an ICV or similar ? If so, where is it located.....if not, any suggestions/pointers ?
Is this perhaps a throttle body needing lubing ? According to receipts, it was replaced a couple of years back (I have had the car about a year).....

Much appreciated, in advance.

[sgould]

The idle control is done by the ECU reading info from the DI cassette. 

I would look for two things first.  A dirty throttle body and a split or fault in a vacuum hose.


It might be a failing DI cassette, but on the later cars than can throw up a check engine light.

The throttle body might also have a crack in a solder joint on the circuit board under the plastic cover.

A vacuum hose fault could be a split or a sticky non-return valve.  There are non-return valves in the pipe to the throttle body from the crankcase vent system.  And valves in the EVAP vent system from the fuel tank.  If it's the latter, it can be disconnected.  Some people have posted this procedure.   I can't remember exactly, but it involves pulling off one of the three hoses from the boost control valve in front of the engine.

[kevpuk]

Thanks for the reply

My Aero is an ex lease car, and has amazingly detailed service history. Both the DI Cassette and Throttle Body have been replaced, approx. 2yrs back IIRC, so hopefully not a failure, per se.
Can you point me in the direction of the throttle body location, and what exactly to clean up ? I will take a good look at all the hoses, in case of perishing etc., but - again - pointers on location would be good.....short of running repairs on a Pinto 1.6 Cortina engine many years back, my recent car engine DIY is extremely limited 

[kevpuk]

OK, so I have found the problem, I believe.

Removing the plastic shroud over the throttle body area, I noticed a white plastic disc-like thing hanging from one piece of hose, and seemingly disconnected from another piece of hose ! The hose goes into the front of the throttle body, as I look at it from the front of the engine bay, and routes along the side of the top of the engine.....seems part of the white plastic thing has remained in the other section of hose (which disappears out of view somewhere downwards in the engine compartment ?).....so, if I can't get it out, will need hose replacing too ?



So, seems this is a non-return valve ? Can it be replaced individually, or do I really need to replace the hose lengths either side too ? Pretty sure the side that has the broken off bit in has been heat-shrunk or similar onto the valve.....

[sgould]

That's the non-return valve in the crankcase ventilation system.  I think it's  supplied complete with hose.  You will be losing air on boost and sucking in extra air when on overrun.  Either way, it will be confusing the ECU as the fuelling will not match the actual air reaching the engine.

[phoenix]

Yes, It's only available as a complete assembly with the hoses either side of the valve. I think the p/n is 59 55 927, rrp 23.53 plus VAT

[kevpuk]

Ta, peeps
Have one en route from nearest Saab dealer (via post) @ £30......slightly more than rrp, perhaps, but in stock and on its way !

How accessible is fitting t'other end of the hose ? Hoping I don't need to squirrel around under the car.....