In-Between Cold and Warm Idle Problem

[TamsDaMan]

This isn't the first time I've posted about this problem, but alas I will give it another shot...

My car does not like to idle when it is in-between cold and warm. It cold starts fine and idles at about 1000 rpm initially until it gets over its cold-cold start thing. After several minutes at 1000, the rpm drops to about 750 and begins to stumble. The ICV will try to compensate over a few oscillations of the idle but eventually it will stall. I work around this by applying just a slight amount of throttle which stabilizes idle until the engine is at operating temperature. Once at operating temperature, it idles fine and does not stall. Occasionally, the idle will oscillate around 750 rpm when warm but it is normally stable. It does not stall when warm.

If I try to restart the car in the in-between cold and warm stage, it will stall almost immediately unless I apply the throttle.

I’ve replaced the coolant temperature sensor, thermo-time switch, idle control valve, idle control unit, the throttle position switch is good, the oxygen sensor is good, I can’t find any vacuum leaks, etc etc.

Could it be the JC chip? I’ve though about this before but I’ve never heard of anyone mentioning it as a problem. Anyone have any other thoughts?

Tom
86 528e

[KevinD]

The oscillation in idle is typically an indication of a rich setting with the idle control cycling more air in to lean out the mixture.

You have to make sure all parts of the ignition are good: distr cap/rotor, secondary (spark plug) wires, spark plugs (use Bosch silbers)and verify gap - .028 inch.

Check fuel pressure, w/engine off and at idle (procedure in Bentleys manual).

I would also pull the AFM and clean the inside if you have some blow-by oil in it along with the accordion hose. Then spray out the throttle body with tb cleaner.

Do you adjust the valves every year or 15000? One mis-adj valve will affect idle characteristics. Adj to .010 stone cold, then rotate engine a few times and check clearances again. Must be checked with the lobe absolutely opposite the eccentric adjuster.

Clean all connections on the main and fuel pump relays. Clean the fuse connection to the fuel pump and make sure it's not loose when you reinstall (use approp size o-ring to pull alum tabs together on the fuse holder if not).

Verify good, clean engine grounds...especially where the injector grounds connect by the battery ground cable to body.

Condition of injectors??? Run some Chevron Techron in the tank after you sort out some of the items above.

[TamsDaMan]

After nearly giving up on this problem assuming it would haunt my car forever, the inbetween cold and warm idle problem is solved. The Bentley basically just glosses over this part, but anyway the only sensor I hadn't replaced was the coolant temperature switch. I had already replaced the coolant temperature sensor, the thermo-time switch, and some other sensor I cant remember, the idle control valve, the idle control unit, etc etc. With a new coolant temperature SWITCH, it cold started fine, stayed at 1000 RPM idle longer, dropped to 750 RPM and stayed there! No more embarrasing stalls as I heat my car up in the morning or as I leave the parking lot. GO 528e!

[Ray7er6ers5er3er]

it look like and does the 535i have it? No problems herr...just want to learn something new.

[TamsDaMan]

Located on the thermostat housing, two terminal spade-type connections. Unsure about other models.

Item 15

[rodpaine]

Here is a picture of these sensors...
Rod's E28 Website

[gomamma]

Tom I have been dealing with that problem for years now and there are 2 facts you will have to accept. I the engine is old and the balance of the cylinders is off to the point where the computer can't deal with it. ALso the blow by gunks up the throttle plate and idle speed motors bad. Yeah you can clean them with carb cleaner and it fixes the problem for a few weeks at the most. But its back all to soon. I recently started removing the throttles and I-speed motors and using chem dip. It cleans better than carb cleaner and gets places carb cleaner spray can't get.
I recently rebuilt a motor with new pistons and did no other changes. It starts right up with no issues and idles smooth... real smooth.

[gomamma]

The whole time I was writing my answer I assumed it was a 535i. Yeah the computers temp sensor on the ETA system does do that. On the 535's it causes a hard starting problem but not a dying when warm problem. Opps My bad.,.