New To Bmw- So I'd Like To Tap Your Brains!

worzel · August 11, 2014

Hi All

I'm new to BMW but not to classic cars- I've mainly owner Lotus Elans which by their design are simpler (cruder some might justifiably say)- but easier to fix certainly.

However, to the point. In Jan this year I bought a 91 525i auto which was advertised as one of those (Timewarp) cars. As it turns out it was pretty accurate description, the body is totally rustfree (even inside the doors) and the blue leather interior is factory fresh.

As usual there are though one or two "issues"- I reckon probably due to minor causes but I'm not sure where to start.

Problem one- I drove it back to Liverpool from Buckinghamshire without any problems (or maybe I didn't notice them) but now I've noticed that when coming to a full stop when the engine is at normal temp there is a momentary surge/hunting for about one or two seconds then the idle steadies.

I've eliminated air leaks as a cause, removed and cleaned the idle control valve, cleaned the MAF and changed the air filter but the problem remains. An un-named garage suggested that at 66000 miles carbon build up was probably causing it but I reckon that's a red herring. the idle control valve was slightly gummed up before cleaning incidentally.

No fault codes are showing- but then again I wouldn't take that to indicate much on its own.

Cold starts are no problem and it idles fine when cold.

Related to this- just how evenly do these engines idle- this is a non Vanos engine that is factory std ie unmodified but it's not quite as sewing machine smooth as I would have thought.

Problem two- are these cars notorious for following the camber? I've had it correctly tracked but it still seems to pull slightly rightwards although at other times it runs arrow straight. No sticking of brakes, tyres are same make, facing the right way (they're directional), pressures are correct, wheel bearings and bushes are ok.

Problem three- this might not actually be a problem. Engaging reverse when at normal running temp produces a noticeable "jolt" in the drivetrain. Have had this looked at but no evidence of worn bushes or prop joints. Gearbox is ZF and oil level is correct, oil spec is correct and oil is about 2 weeks old. I know some auto boxes do have a tendency to produce this kind of noise when selecting reverse but is it normal on these?

Last question- not really a problem but can somebody explain how the heating system works? The auxiliary electric water pump I imagine boosts the flow straight from the rear of the block and pumps this into the heater valve. When hot is selected I can understand how this works but what about when cold is selected- does this pump work continuously while the engine runs or does selecting cold throw a switch somewhere that shuts off the current to the pump because surely if the pump does run continuously even when cold is selected it is still collecting hot water from the block- or have I got this completely wrong?

Regards

John

worzel · August 17, 2014

Hi

Can anyone think of a reason why the Idle Control Valve couldn't be moved to a more convenient location away from underneath the inlet manifold on a 91 525i?

This would mean a bit of hose modification and fabricating a new mounting point - possibly adjacent to the MAF but doesn't look overly problematic or are there any technical reasons why the airpaths for the attachment hoses to the ICV have to be a certain length?

Regards

John