E34 535i M30 Idle Problem

[ChitoD]

Low (94k)mileage 1989 535i hot or cold starts immediately but idles at 1,400 rpm. After around 2 minutes idle oscillates between 1,300 1,500 rpm. Check engine light is on and stomp test shows code 1262 (Idle Control Valve). Previous to this problem car ran great.

Things done:
1. Cleaned ICV - no change.
2. Replaced with brand new ICV - no change
Tested ICV connector - correct voltage.
3. Had Air Flow Meter professionally tested - no problem
Tested AFM connector - correct voltage
4. Adjusted & checked Throttle Position Sensor - Okay
Tested TPS connector - correct voltage
5. No apparent vacuum leaks.
6. Tested Engine Coolant Sensor - okay
Tested ECS connector - correct voltage
7. Valves adjusted - no change

Only thing not checked/replaced is Oxygen Sensor. Could a defective sensor be causing the fast startup idle and the oscillating warm idle?

What else should I check?

[Paul in NZ]

how long did you leave the new icv on,things can take a whle to settle down again.....

[ChitoD]

New ICV was installed 3 weeks ago, but no improvement. Car idles too fast to be driven regularly. Thanks.

[Martin in Bellevue]

Sounds like an air leak. Replace hoses, especially that 1" wide hose from the ICV to the lower part of the intake manifold; the hard to reach one. Then, check the hose to the bottom of the intake manifold to the air cannister. There are also 2 thin vacuum lines off the manifold to the fuel pressure regulator & the valve cover breather. Then, check the lines to the brake booster; there is a nipple on the check valve that needs to be capped.

[Jeff N.]

.

Sounds like an air leak. Replace hoses, especially that 1" wide hose from the ICV to the lower part of the intake manifold; the hard to reach one. Then, check the hose to the bottom of the intake manifold to the air cannister. There are also 2 thin vacuum lines off the manifold to the fuel pressure regulator & the valve cover breather. Then, check the lines to the brake booster; there is a nipple on the check valve that needs to be capped.

[ChitoD]

Thanks for the tips Martin. I will check the above this weekend.

[emw525E34]

This may sound silly. But is the throttle cable too tight ?.
This might simulate gentle stepping on the gas pedal.

[shogun]

I hope the link works, have no access to RF. AFM adjustment. Maybe someone can download it and post it here as safety copy
AFM Adjustment for BMW M30


http://
members.roadfly.org/louielouie/AFM_adjustment.html

then I found the following:
To measure the AFM:
1. Unplug its connector and remove it from the car.
2. The connector on its side has 4 pins (#5, #9, #7, #8 left to right). To measure its potentiometer resistance you put your voltmeter (set to resistance) probes on pins 7 and 8. Then move the flap by hand from close to full open. You should measure a resistance something like 2400 up to 3400 Ohms (something like this) smoothly and gradually increasing as you move open th flap. Also note the flap's spring tension. The flap should feel like it has consistant and even spring tension all the way through from closed to full open.To measure the Intake Air Temperature Sensor:Put your Ohm meter between pins #9 and #8. At room temperature you should be measuring 2200 to 2700 Ohms. Now get a hair dryer and blow warm / hot air through the afm. The air temp sensor resistance should drop down to a couple hundred ohms or so. It's good to make sure the air temp sensor is working because it also helps the ECM decide on the spark-ignition timing. If it's not advanced enough then you'll lose torque and fuel mileage. If it's too advanced then you'll get detonation.

And here as people say the most definitive guide to testing and rebuilding an AFM...
http://www.the944.com/afm.htm

[genphreak]

If faced with this one I'd suspect the 02 sensor.

Have seen it cause this sort of thing before the ECU figures out it's bad. I;ve also done the AFM cog advancement and found it helped in the short term but not in the long once the ECU had been able to monitor operation for a while. Like so many things, no-one reports results on these adjustments without taking the care to measure results before the change (with a reset ECU) and with a reset ECU after. (Though to get it right one really needs to reset the ECU, drive (>100km), measure, reset again, make change, drive (>100km)... bah!)

[Derek A.]

If you are starting the car cold and it has the affliction - it cannot be the o2 sensor as its not in open loop mode. The car is ignoring the o2 sensor input until it warms a bit.If my memory serves the idle circuit is pretty sensor free, the values are set in the ecm based on the activation of the idle switch. I think you have a vacuum leak that is hiding. I would start by getting some fresh hose and capping off all the taps on the intake and any of the other ports. What you want to do is isolate every possible source and see if there is a change. You can also do thinks like block the air intake altogether and see how the cars runs. If you seal off the area in front of the AFM and the car still runs - then you know that its sourcing air form another location. Its possible that you might have a bad brake booster and its leaking air. So isolate the engine and see what happens.