BMW E28 520i high idle

[r31mark]

Gday there lads

My name is Mark and I own a 1983 Australian BMW E28 520i. The car idles at 1800-2000rpm and I need help to figure out what is wrong.

Background info

Car:1983 E28 520i

Engine:M20B20 6 Cylinder

Management:L-jetronic


The Problem

When the car is started the idle starts to creep to 2000rpm within seconds, and maintains a high idle for roughly 10 minutes, after such a time the car may start to pulse from 800-2000rpm.


Symptoms

-high idle

-smelly (I really don't know what type of emissions you'd call it but it just smells like it would probably be bad for you)

-engine cooling system/hoses heat up really quickly


Things I have done so far:


I have cleaned the throttle body and the maf with carb cleaner,adjusted the valve spacing or whatever it was called (did this ages ago), replaced the exhaust manifold gaskets, done a sort of leak test with a spray bottle with soap in it (didn't really find anything). I am currently replacing the additional air slide valve thingo (its like a second thermostat) as mine doesn't open as much as I think it should, and I'm about to replace a hose plus add some hoses to some places where they are missing to see if it makes a difference. These small hoses will come from the tb, run to what I assume is the egr (mounted with my airbox), which will then go to the airbox thingy on my distributor, which will run to the T piece which I have on my intake to icv line.

I'm not entirely sure what I'm doing here, I presume that the previous owner of this car hasn't really known what they were doing and has probably disconnected some hoses and maybe 'wired' some wrong or something.

I have also found a video online of a car with a problem that sounds EXACTLY like mine. See:




So, anybody have anything to say that could help me?

[ejenner]

It will ALWAYS be an air leak. Engine speed is controlled by the amount of air entering the engine. The fuel is added afterwards to combine with the amount of air coming in.

Things you can look for:

1. Split hoses. They can look ok but until you've felt all around each intake hose you won't know if there are any splits in it.

2. Hoses not properly attached. If a clamp holding a hose on has been misaligned as it was tightend it can pop off of what it was supposed to be tightend to and will actually create a gap.

3. In some designs the crank case breather system can allow additional air into the intake tract if there is a fault. For example, if the valve cover gasket has failed or is pinched or something like that. Additional air can get into the valve cover, then go down the oil breather hose and add additional air to the engine.

4. The idle control valve. You can try squeezing the hoses around the idle control valve to see if the additional air is coming through those hoses. If it is that then test the idle control valve and replace if necessary.

5. VAC hoses, all the small 4, 6 or 8mm rubber hoses should be attached. If you see any missing it's ok to cap off the nipple the hose connects to. Manufacturers occassionally added additional ports for vac hoses in case they would be required later or for other specifications. If everything else is connected but you still have spare ports it is possible the cap has fall off. VAC hoses are extremely prone to leakage. Sometimes a VAC hose can leak along it's entire length just bcause the hose is perished.


The video of the engine you can hear a hissing sound, that's the air leak.

[r31mark]

Thanks for the great reply ejenner

Do you think 'smoke test' would be a wise thing to conduct on the car? Apparently you can get some dry ice and make your own smoke machine pretty easily, I think I'd be capable of that.

Cheers, Mark.

[ejenner]

No, it's not going to hurt it... but you'd be wasting your time. Careful checking of the intake tract would be your best bet. For best results take off everything after the air mass meter up to the inlet ports (i.e. including the inlet manifold) - clean and inspect all parts thoroughly looking carefully for cracks and then reinstall with new seals. The worst that can happen is that you'll end up doing all that work and find you've not fixed it... but on the upside, you will have eliminated all intake parts and your engine bay will be nice and clean in that area.

It's not very easy but sometimes you're able to go around the engine with your ear close to particular parts and you can find where the hissing noise is.

Buy some silicon VAC hose as well. Replace all the VAC hoses with new. It's not expensive. Make sure you get the right diameter for your car.

[bavarianretro]

Good advice. On an l-jet car, vacuum hoses would be my first port of call.

[retrowrongun]

Will be an air leak as a lot of pipes under and around inlet manifold split on them
Also make sure the maf is properly cleaned and if it has the flap type make sure it s operates smoothly

[r31mark]

Alrighty, I'll take everyone's advice. I think a rebuild of my intake setup would be a great thing to do. And silicone hoses you say ejenner? why do you suggest these as opposed to the normal type hoses that can be bought? where do you get them from?

Thanks, Mark