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A friend has an e36 that wont maintain idle.

The car is driveable but coughs and stops when idling.

I've checked the air box and boot and they are in good condition - no leaks. I think spark and fuel distribution is fine too as there is no missing when the car revs.

Would anyone know what could be causing the issue? IAC valve?

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    I wouldn't trust the spark and fuel to be correct. You need three things for an engine to run: Fuel, spark and compression. The right air/ fuel mix delivered evenly to each cylinder. A healthy spark with the right timing, and good compression on each cylinder. Many factors could affect those things above in such a way that the engine runs poorly at low revs but problem is hidden when run at higher revs. Dirty plugs, old/dirty fuel, incorrect fuel mixture, broken high tension leads, faulty ignition coil, burnt valve, worn piston rings. Don't assume. Test the individual components. – Sir Swears-a-lot Jan 6 '15 at 10:04
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    What engine does it have. Is it a 318, 320, 325 etc. Petrol/diesel? Variable valve timing? Carbed/injected? When was it last serviced? Has it been parked for a long time or is it driven every day? – Sir Swears-a-lot Jan 6 '15 at 10:11
  • Looking at your profile I see you're in Brisbane. Is the car near you? If so that means hot/humid now. – Sir Swears-a-lot Jan 6 '15 at 10:18
  • @Peter ... Actually, the three things you need for an engine to run are: air, fuel, and ignition (some way to make it go boom). – Pᴀᴜʟsᴛᴇʀ2 Jan 6 '15 at 12:19
  • @Peter thanks peter. It has the 1.8 Petrol with injection. Not sure about VVT but I doubt it. Was last serviced 4 months ago and is a daily driver. We replaced the fuel so its not a fuel quality issue. – MeltingDog Jan 6 '15 at 23:29
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I had the same problem with my car last year, problem only occurred when idling and not while driving. This is why I immediately suspected the IAC.

Removing and cleaning the IAC did the trick for me.

Hope this will help you.

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You can actually insert programming scripts into your ECU. Palmer Performance has a variety of adapters and computer software. I know they have some kind of script library, or you could try replacing the computer. Have someone check your distributor. If it's throwing check engine codes, take off your valve cover and tighten the studs with a breaker bar but be easy. It only take about 60 lbs. on each stud but if they're rusted ur gonna have to break it loose first. Then I would look at smaller things, learn how to check the valve clearance with a feeler gauge, you'll need your engine specs to, and some knowledge on the firing order. If you want to do a head gasket you better have lots of tools and possibly a week to work on it, and about 500 bucks in case you break your knock sensor and have to pay a mechanic to finish the job for you.

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