81 528i - rough idle question

[Some Guy with a BMW]

Hi,

81 528i - 5speed - N.American car.

Idle is rough - nearly wants to stall at times, searching up and down (revs up and down to near stall, then up again).

Give it gas and it instantly smooths out. Drives fine, and idle improves (though not where it should be) when it warms up.

Any tips/thoughts/ideas of where to begin?

Thanks,
Chris

[T.Hanson]

There is no one stop quick fix or screw to turn. The engine's running properly is a function of all the parts, pieces and variables doing what they are designed to do. If that is obvious, so should be your mission to check the items on the list. Or take the car to a shop to have it done in trade for money.

Read previous posts about adjusting the aux air valve. Cleaning, checking it is working, adjusting the throttle switches, then the big brass idle screw in the throttle body.

After or before that,... the plugs, wires, timing, oil, fuel filters, brake fluid, coolant,... maintenance items that count in a 37 year old sled.

[Some Guy with a BMW]

Thanks very much.

I've been living in carburetor land for a while now, so just checking in where to start.

Something like the aux air valve is what I was looking for, and I found the FAQ on it. I'll play with that then move on.

I'm not driving the car now, so I plan of slowly sorting it as time allows.

I also plan on of course the rest. I did an oil change first thing, coolant is relatively new, but yes I'm going to look at the plugs and definitely replace the fuel filters.

[Some Guy with a BMW]

Sorry, just to follow up - if I read the FAQ correctly, I should fiddle with that 7mm adjustment nut on the aux.air valve, and if the idle (when cold) responses then the value is working, but if nothing happens, the valve may be out of action?

[Robert Bondi]

The only thing that valve really does for you is adjust the idle speed when cold. The more that valve is open at cold start, the higher the idle speed will be. I'd fix your warm idle first. If you pinch off the hose coming out of that valve and going to the manifold when the car is warm, you'll eliminate any effect of that valve and be able to troubleshoot the warm idle.

Sorry, just to follow up - if I read the FAQ correctly, I should fiddle with that 7mm adjustment nut on the aux.air valve, and if the idle (when cold) responses then the value is working, but if nothing happens, the valve may be out of action?