960 Idle Hunting - What is an Air Intake Valve?

Hi All,

Sorting of the 960 moved a step closer today after I had the gearbox oil changed: What a difference! It feels like a different car and is well worth the money.

At the same time I asked them to investigate my erratic tick over. The problem only manifests itself when the car is in neutral or park. It will generally tick over (smoothly) at just below 1000rpm, but will then dip to about 500rpm briefly before recovering to the higher level for about another 10-20 seconds. It is very rhythmic and never cuts out.

When in drive and at standstill, the car idles rock steady at about 800 rpm without fluctuation.

The garage said that the fault codes indicated that the Air Intake Valve was at fault and they claim to have swapped out most of the rubber pipes from the inlet tract to make sure that there were no leaks or blockages. They even disconnected the battery to clear all faults, which came back when the car was run.

So, I wondered if anyone here has had a similar problem and if anyone knows where I could buy an Air Intake Valve at a more reasonable rate (£160 + Vat from Volvo!)

I've read the long message thread started by MvE back in 2002, but his problem was not resolved and the symptoms don't really match with this problem as the tick over is silky smooth when in gear and between 'dips'.

Thanks in advance, once again,

[Chesh740R]

Not sure what Long message thread was by MVE but i had a simular problem on my fathers 960.

Which i traced to a blown inlet manifold Gasket.

With the car idling, very carefully spray some brake cleaner over each port, if the car stutters or changes over a certain port then its that.

My money would be on Number 1 intake near the front of the engine.

Volvo even upgraded the intake manifold gasket part due to the failures.

Gasket is about £25 and the dealer quotes 2-3 hours to change it at there silly labour rates.

It looks daunting but its actually a very easy job and i completed in about 2hours myself.

[Peter Milnes]

The air intake valve is usually fitted in the inlet tract of the filter and is thermally operated. It selects either manifold heated air or cold air from the front of the car. These have been known to suffer failure of the thermal operating device. Are you sure they didn't say "Idle Air control valve"? The symptoms you describe are very similar to those of a faulty Valve which is operated from the ECU via the throttle switch when throttle is closed.

All the best, Peter.

Thanks for both replying,

Chesh - I'll try the brake cleaner.

Peter, the receipt that I have in front of me states: 'Suspect Air Intake Valve'.


Is the Air Intake Valve a simple thermal device or would a faulty one be able to generate fault codes? You see the mechanic stated that fault codes were being generated indicating that it was the Air Intake Valve. If the Air Intake Valve is a 'stand alone' item it would perhaps indicate that he has got his terminology wrong and that he meant the idle air control valve!

Is there a way of inspecting or testing the IAC valve to see if it is faulty?

Thanks

Peter,

I have just been out and changed my rear discs/pad, after which I decided to observe my tickover problem from cold.

The problem does not manifest itself until the engine reaches normal working temp, should this give me any more clues or definate pointers to the cause?

Also, can you (or anyone) tell me where the idle air valve is please and how to get it out?

Thanks

Adam

[Peter Milnes]

Adam the garage means the preheating shutter when they talk about the Air Intake Valve. The fault tracing procedure for this starts with checking the radiator, air duct and air cleaner (housing and insert) for blockages. Next with engine idling put your hand on the preheating hose where it enters the cleaner housing. It should be at ambient temperature. If it is hotter than ambient the shutter in the cleaner housing should be checked for leakage. The fault list of items to check for the problem you have is 1) Timing retarded due to knock, 2) Damaged Ignition coils, 3) Blocked air cleaner/air intake, 4) Uneven compression, 5) Low fuel pressure, 6) blocked exhaust system (usually catalyser), and 7) Faulty sensor signals. So if the Air Intake Valve (preheating shutter in the cleaner housing) checks as OK let me know and I will send you a copy of the relevant pages.

The Idle Air Control Valve is situated at the left (passenger side) middle of the engine, where the air inlet hose feeds into the manifold. It has two hoses and an electrical connector, which carries the operating signals from the ECM. It should operate at idling only.

All the best, Peter.

Peter,

Thanks very much for all this info, it's really appreciated. Just 2 more question for now if that's OK:

Will the preheating shutter generate fault codes? (Because if not I guess that it can't be to blame as the technicians' found error codes)

What would you start with (ignoring the garage's prognosis) taking the symptoms into account?

Thanks very much for all the help.

Hi Peter and Chesh,

I've managed to sort the problem and I hope that it was caused by a dodgy connection.

I decided to have a delve into the air inlet tract to have a look at all the bits, so that I could relate to what people are saying. Firstly I took the air cleaner apart and removed what I presume is the air mass sensor (black plastic 'T' shaped thing). I initially thought that it must be the idle air control valve, but as it did not appear to have any moving parts I decided that it couldn't be.

I next removed the aluminium cylinder thingy that mounts by pushing into a ring in the inlet rubber, which I presume is the IAC. Didn't take it apart, I just had a good look and wiped some muck out of the exposed hole. The connector did look a bit dry/corroded though. Put it all back together and bingo! No hunting. Took her for a drive, came back and let her tickover until the fan came on twice and no hunting what so ever!

Thanks for you help and support. Right what's the next job......

Rattling cat.......I don't suppose you've got one laying around?...