Loudgoldwing

{Original post from Monday sits unanswered in the A4-B5 forum...}

Hi,

My name is Sean, and I just bought a '98 Cabriolet with 60,000 miles. The vehicle appears to have been VERY well cared for, but I am having an odd issue. I've searched high and low in your forum, and I've found close issues, but not quite mine. I wouldn't even be asking you guys about this, but I want sincere input instead of loading the "parts shotgun" at the word of a service writer (yeah, I know, I'll get there. Sorry).

So... here goes...

Every stoplight I hit, if the vehicle sits for 20 seconds or more, regardless of the engine's temperature, the RPM's will drop suddenly. 9 times out of 10, the engine will recover. 1 out of 10, it will die completely. (Doesn't seem to be an issue while the vehicle is warming up in the morning.)

I've found that if I hold my left foot firmly on the brake, and gently tap the gas with my right foot about every 15 seconds, this issue doesn't happen again. It kind of "resets" whatever countdown starts when I come to a complete stop. I would prefer, however, to resolve this issue instead of having to tap the gas while stopped.

My first impression was a faulty or sooty Idle Control Valve (Idle Control Circuit in an Audi?) However, a service writer at the dealership nearby said that my problem was the Engine Coolant Temperature Sensor. So, I stopped at the parts counter to get one, and the guy at the parts counter asked me "Which one?" He then pulled out an exploded diagram. There are two, according to this diagram. Both (apparently) on the gloss black metal coolant line running behind the head. One on the driver's side, and one on the passenger's side.

"Unless..." the parts guy then told me, "You might have the model that only has the one sensor... It looks like that sensor does both."

So... one sensor for the gauge, and one sensor for the mixture control. Unless there's only one, in which case it does both. Sweeeeet... Which one's which? But then I had a flash of brilliance.

I went out and grabbed the registration, so Mr. Parts Guy could use the VIN in order to get a better idea of which sensor I might need...

Yeah... Uh, no luck. He still couldn't tell me. Why? I have no idea.

So, he gave me a sensor with the green square plug and the diagram, and said, "Here, take these out to your vehicle, and see what you can find..."

I've been wrenching bikes for 10 years, and do all of the basic maintenance on my ML55, and I tell you, I couldn't even see the damned coolant hose that supposedly runs behind the engine, and has outlets into which one would plug these sensors.

So, I gave the stuff back to the parts guy and left, feeling like an idiot. However, I am a stubborn 37-year-old man on a prescription of Adderall, so once I get a hold of an issue like this, I chew on it like Beef Jerky. That being said, here's what I've observed since early this week...

This vehicle does seem to take a WHILE to get up to what I assume is normal operating temperature (the second line up after the orange area, it's thicker than the others). So, thinking the thermostat is dodgy is logical. I bought one, and I will install it this weekend. At 60,000 miles, I feel the need to check the timing belt anyways. HOWEVER:

I intentionally let the vehicle sit until the gauge got all the way up to the thick line. I let it idle, and sat there and tapped the gas every 15 seconds for 5 straight minutes... When I stopped tapping the gas, the bastard still did EXACTLY the same thing. 20 seconds, then stall. So, it seems that my issue isn't temperature-related. Or, I guess it is a temperature-related mixture issue that has pushed another component past its limit.

Following my first instinct, I have found an idle control circuit... but if the service writer is right, it would only cost me $50 for a coolant temperature sensor instead of $200 for the idle control circuit, so it makes sense to at least ask before pulling the trigger, right? I could REALLY use an expert's opinion on this. Does this guy's suggestion carry any weight?

I SWEAR TO GOD I'm not the typical newb who is looking for an excuse to buy the cheap part, here. I just want to do this right, and I'm unfamiliar with the quirks of this specific vehicle. If any of you folks have ever owned a MB W163 ML, you will understand why I feel a connection with this car, and want to give it the love it deserves.

So, please ask me as many questions as you'd like. I'll give you as many details as I can in order to solve this issue. This is seriously the only major problem with an otherwise IMMACULATE vehicle.

Well, there's the transmission, too. But I'm sure your eyes are tired already, so we'll just leave that for another day, shall we?

Thanks guys!!!

Loudgoldwing

Found the tech article. No clue how I missed it earlier. Really sorry guys.

maineman

Let us know how you make out with that .

CRAZY_RUSSIAN

he could not tell you, cause your car is too old! ETKA only works with vin starting from about 99/00 years :-) ask me how i know ;-)

Loudgoldwing

To clarify... found the tech article on how to clean the ICV. Doing that this afternoon. As for the thermostat, didn't realize I would likely need to remove the timing belt in order to get to it, so I'm going to let a pro handle that in the next week or so.

What does ETKA stand for?