Q. I seem to have a problem with the idle speed of my G60. Its fine when cold , warming up and when at normal temp. However if I'm sit in traffic and it gets a bit hotter then the idle speed goes upto about 1500rpm and won't come back down until the car cools down again ,say when I get on the open road . Its usually starts to be a problem when the water temp gauge goes above about 100C

WARNING - this got kind of long - sorry for the verbiage...

Hi Alex, (and Alan with the related problem)

There are a number of things that this could be:

1. ISV - Idle Stabilizer Valve [Especially Alan whose problem is when the A/C is on.]

When the A/C compressor is on, it req's a jump in electrical power - which causes the load on the alternator to increase - (also the compressor puts extra drag on the accessory belt as well) - which will bog the motor down - the ISV will sense this and compensate by increasing the engine speed back to idle - If the ISV is faulty (usually an internal leak of sorts) the idle will hop around.

The ISV compensates for all sorts of problems that might be happening (when it is working correctly) BTW, the ISV on the G60's also acts as a wastegate of sorts, venting excess boost in certain situations. Also, the ISV is considered by VW to be an electrical part - hence not returnable to the parts guys if it turns out it is not your problem - I had to beg my parts guy to let me return it within 1 hour if it didn't cure an idle problem I had a few years back - thankfully for him, it cured it. Very easy to replace - One electrical connection, two hose connections. It is a t-shaped thing about the length of a soda can; located right on top of the cylinder head towards the passenger side.

Cleaning the ISV (for ex. w/ brake cleaning fluid) works sometimes. Remove the ISV, spray it, shake it, drain; repeat until the stuff coming out is relatively clear. Let dry. Initially, the idle will be all crazy and such but it will go back to normal. This will work some of the time but not in all cases. - it worked for me on my G60 until I finally had to replace the ISV outright when it stopped doing the trick.

2. Coolant temp sensors There is a direct connection between the coolant temp sensors and the ECU. Since your problem seems to related to engine temp, this might be a cause. The coolant sensors are located right in front of the head - one is blue, the other either black or white. If I remember correctly, the blue one is for the ECU. There is a test procedure for it - if you don't have the Bentley book, I can look it up for you and let you know what it is.

3. Vacuum leaks Engine idle is very dependent on the presence (or should I say retention) of vacuum. Look for cracks or leaks in any of the vacuum lines (often cloth-covered and about the diameter of a pencil) Also, things like the red/orange dipstick holder, T-connectors, etc.

Common places for cracks/leaks are behind the throttle body (there is a short piece that goes from the TB to the FPR (Fuel pressure regulator) that sits behind the TB) and also the length-critical 1m long hose that goes from the engine to the ECU. Engine heat eats away at the rubber over time.

4. Grounds There are a number of places that the engine block is grounded to the chassis - also the ECU needs a ground. Check the ground wires to the throttle body (I believe that there was a TSB that recommended moving one of these so as to lessen the chance of it breaking under the constant movement of the engine itself) As an exercise, check the condition of all of the connectors and wires in the engine bay - there really aren't that many - a little elbow grease in shining up connectors along with a shot of dielectric grease will ensure good connections and keep gremlins at bay.

Well, I've left out some things but I hope that helps to get a good start. BTW, if the dealer says you need a new ECU for the idle problem, make sure you get a 2nd opinion!!! Dealers tend to want to blame the very reliable ECU for a lot of things (read: they cost a lot and are easy to replace)

Hope that helps!

Yosh

'71 Karmann Ghia Cabriolet, '90 Corrado G60 Stage II