My '97 A8 (4.2l) has been stalling out when first started cold. If I give it a little throttle it will stay running unless I take my foot of the pedal. The RPMs will jump up briefly as the idle valve tries to kick in, and after about 30 seconds the idle valve starts working normally and it runs great.

I've replaced the idle valve with a brand new Bosch unit (for $302!) but it still does the same exact thing.

The check engine light does come on with an error of intermittant power to the idle valve (don't have the actual code right now).

Does anybody know if there isa temp switch or sensor that controls the operation of the idle valve?

Any help is greatly appreciated.

Cheers,

Jeff

 

I believe the coolant temp sensor sends signals to the ECM so the ECM knows what temp the engine is at. If the engine thinks the engine is colder than it is or warmer it will affect how the Idle air control valve will work. I would start there, its like a $40 part.

 

any fault codes? coolant temp sensor/thermostat when was it last serviced? + it could be a multitude of issues but no fault code leave me in the dark

 

Thanks for the replies. Do you know which temp sensor (green or blue) I should start with?

The error code is: 17917 (P1509), Idle Stabilization Valve, Electrical Problem in Circuit, Error occurs intermittently.

The vehicle was completely service 5K miles ago, including a new timing belt, pulleys, and water pump. It runs like a champ, except that first cold start.

Cheers,

Jeff

 

green but consider the thermostat as well

 

Cool. I'll start with the green one. It's a PITA to get to, but at least it only costs $22 for a new Bosch unit.

We replaced the thermostat when we did the timing belt/water pump.

Cheers,

Jeff

 

P1509 is idle air (IAC) valve - circuit malfunction possible faults are wiring, IAC valve, as you say its intermittent and you just had work done I would check the wiring and connections ( ive also seen the temp sensor cause this problem ) because it doesn't give a correct reading and causes flutter/idle issues

 

Replaced the green temp sensor today... no change. It fires up and dies unless you hold the throttle open a bit. After 20 or 30 seconds, everything works great.

The timing belt/water pump replacement was done last September and this problem just started happening last month, so I'm doubtful that there's a connection. Additionally, the fact that the problem goes away after it warms up a bit makes me doubt that it is a wiring issue.

Unfortunately, I don't really know where to look on this engine. If it were a 1.8T or a V6, yes. But these V8's are mostly a mystery to me.

Any help is appreciated.

Cheers,

Jeff

 

Have you tried cleaning the tb? I know on some vehicles the passages to the IAC can get kind of clogged with crud over time. Just get your self some BG throttle body cleaner or similar. Just a thought.

 

Well... here I am a month later and the damn thing still does it. The temps around here have warmed up so it only does it early in the morning when the outside temp is below 60.

I'm still hoping someone may have an idea. Anyone??

Anyone want to buy a '97 A8 with a cold start problem? Cheap!

Cheers,

Jeff