VANOS seals?

[ScottyWM]

Posting this here because I've learned this is where the best advice is! (I also posted this on an E46 forum.)

My daughter's car, which I only see a couple times a year to work on, has this surging at cold idle problem. Sometimes, if you let the surging progress (sitting at idle), it will eventually stall. Once the engine warms up just a little, the surging stops. And, we just noticed that sometimes (only twice actually), that when it does the surging, the temp needle will peg out Hot - even though the car was just re-started and we know it's not hot at all. Turn key off, back to on, and temp needle will be normal. I just changed the thermostat because the car was running cold, and now it is heating up properly. I was hoping changing the thermostat would fix these problems, but it didn't...

Does this appear to be bad vanos seals? The car has 135k miles on it, and had been dealer maintained before we got it a year ago.

Surging RPM:


Then after turning the car off restarting:

[billb]

Did the Vanos seals on my '01 325 Scott, and I still get the cold-weather surging occasionally. I think it's more lazy ICV than vanos seals. Can't really say that the seals evened out the idle, but they seemed to even out the low-medium throttle response. Also check for a tight-fitting DISA valve; the seal is known to leak on that, which would bring in unmetered air, further complicating the ICV issues, especially when cold and more gaps due to seal-shrink.

As for the temp needle, my guess is that it's getting stuck out there when the engine goes into the wild swings and the cluster goes to the engine off/switch on gauge test. 'bout all I could come up with there.

[genphreak]

The hunt is the engine getting bad input- the intake and coolant sensors may be faulty as you would have thought but the wild fluctuations are voltage related. If the engine stalls or almost stalls this is probably the cause of a sudden drop in voltage which may do that or upset the ECU or even the voltage the O2 sensor feeds it.

How old is the battery, O2 sensor and spark plugs?
Best to test the engine coolant temp sensor as they do fail... if it reads badly the mixture will be incorrect, the o2 sensor readings will confuse the ECU and the idle get adjusted incorrectly causing voltage drops and stalling perhaps.

[shogun]

as for coolant sensors: often the coolant and any other sensor are still o.k., main problem are the connectors and the thin wires in the connector wire loom, they easily break. That is most important to test the wires. Also the wire plugs fail, the plastic breaks and then the cable connectors retreat/move inside the plug, so that actually the pins of the sensor and the wire loom plug are not connected.
Have seen many of these problems, also with wash water pump wires, coolant sensor wires and so on, all these wires are very thin and now after 20 years or more can break very easy.

[bubba]

The idle issue you are seeing is your vanos seals, the following link will give you everything you need if you want to do the vanos seal replacement yourself: Beisan Systems. As for the temp indicator, I agree with billb, as I have experienced your exact problem with my temp needle. I'm in the process of replacing my vanos seals with an upgraded kit from beisan systems.

[ScottyWM]

Yeah, seen the Beisan systems repair site. Do you have the same/similar idle swing? What model car are you doing? Keep me posted with your results!