Idle valve freezing
 

Hi all,

I'm having a very weird issue with my idle valve. The car is a 4.2L 1997 A8. When the temperatures dip below -18 degrees celsius, my idle valve gets gummed up and frozen. This only ever happens in the extreme cold.

This is what the value side and engine side look like:

Attachment 25310

Attachment 25311

The valve was frozen stuck to the point where I couldn't even move it with a plastic pick. I had to scrape whatever was on it off and spray it down with some throttle body cleaner to free it up.

Has anyone come across this issue or know what that stuff is? It smells like oil to me but I'm not sure why it's freezing up like that.

Any help is greatly appreciated.

Thats an emulsion made up of oil vapour and water vapour (like mayonnaise) which typically happens when the car is used for lots of short journeys as it never gets hot enough to 'burn off' all the moisture in the engine. The solution is usually a good long run to get everything hot and keep it hot for a while. Ideally an hour or more on a motorway will do it as the engine needs to be under load to generate enough heat, although if its -18 where you are that might be tricky to achieve?

Back in the 90s, in my capacity as an electronics design engineer/programmer, I developed a fuel injection diagnostic device that also had an injector and idle control valve cleaner function. Idle problems due to clogged/dirty ICVs were a very common problem back then and most attempts to clean them in situ resulted in a fix that was temporary at best.

I'm guessing that a '97 A8 has the same early type of solenoid-based ICV. Later ICVs were controlled by stepper motors and were less prone to sticking. The solenoid type usually has 2 or 3 terminals. The 2-terminal variety are a simple spring loaded solenoid .... just apply power and it moves one way, remove power and it returns under spring tension. The 3-terminal variety use the additional terminal to reverse the direction instead.

What we found during development was that it was necessary to fully 'exercise' the solenoid, preferably while submerged in a cleaning solution. I think we used some sort of injector cleaning solution/detergent, but carburettor cleaner might work too. The most important thing is to pulse the solenoid from one extreme to the other while cleaning. In normal operation, the back and forth range of movement of the ICV tends to be much less because the ECU uses PWM (pulse-width modulation) to move it to the required position, so eventually scum-lines build up inside the mechanism either side of its usual operating range. Pulsing the solenoid back and forth to the extremes while cleaning helps to remove the scum-lines. The solenoids are not designed to be powered for long however, so its important to keep the pulses short (<1s) to avoid damage.

Edited to add: It's also important to observe the correct polarity when pulsing the ICV because they often contain back-EMF suppression diodes connecting internally across the terminals.

Having said all that, given that problem seems thermally related, it's also possible that the solenoid has an internal fault -- A broken winding wire can result in similar symptoms, making and breaking the circuit due to expansion/contraction as the solenoid temperature changes. However, it might be that the gunk is becoming more gunky when cold so I think it's probably worth trying a thorough pulsed-clean first.

My engine has had issues warming up to operating temps, so i'm suspecting a faulty thermostat. This probably isn't helping too much with this issue. I've had trouble getting it up to 90 degrees even in the summer months. Timing belt service is planned for when it warms up.

As a temporary solution to get it warmed up, would it be safe to block off part of the radiator with cardboard? My worry is that I don't want the trans temps to skyrocket if I do that.

Would an oil catch can help in this situation? The other temp solution I was thinking about is venting the PCV to atmosphere, but that probably isn't the best idea.

Thanks all.

Thats definitely not going to help. If the engine never gets up to temperature its never going to evaporate all the moisture and its probably getting fairly unhappy inside.
The transmission cooler is integrated with the engine coolant so that isn't getting to temperature either.

Blocking the rad may help I guess. Venting the PCV to atmosphere is likely to result in it getting blocked with ice at -18 so probably not a good idea. A catch can isn't going to help either if the problem is the thermostat.

It would be nice to know at least where you are domiciled. Temperatures as low as you are reporting is certainly not UK.

I'm over in Canada. We got about another week or so of colder temps, so I'm going to block off the radiator and try to get this thing up to operating temps to get rid of the moisture.

Would it be worth it to do a quick oil change to take out any excess moisture from the crankcase?


Edit: The correct fix of changing the thermostat is coming this spring. Unfortunately a bit chilly to do it right now.

'-18' and a 'bit chilly' would be rather incongruous in the UK. Brass monkeys would be living in fear.

Two of my old Army College friends live over there. One in Toronto and one that has moved up country from there.
The photos they send me are interesting.