A4 Kept Stalling Now Won't Start At All

[S-lime]

EDIT: REPLACED THROTTLE BODY AND STILL GIVING CODE 17953 Throttle Valve Controller: Malfunction

2001 Audi A4 Quattro with a 1.8t with a diode mod running 14lbs of boost. A few days ago it died randomly out of nowhere. Tried turning it over continually and it wouldn't start. I got it to start by turning it over shortly, turning the key all the way to off and repeating. Throughout the past two days, it has died 3 times. All times it would start up immediately after by turning over and turning off until it started. Today it started fine as usual. As I was letting it warm up it died. It won't start at all now. I immediately checked the fuel pump, it is getting power and pumping fuel properly. I am 100% certain I need a new diverter valve, as it has needed replacing for close to a month now. I don't believe this is the issue. Where should I start looking? What are your first guesses?

[CoyneJ]

sound like fuel, any codes?

[walky_talky20]

A blown fuse wouldn't explain the intermittent issues.

I think a faulty Engine Speed Sensor (aka: "crank position sensor", "CKP sensor") might be to blame.

Please check for codes with VCDS and report which codes are present, regardless of whether the check engine light is on or not.

[S-lime]

So I scanned the codes. I keep getting two codes: 17939 - Camshaft Timing Adjustment: Open Circuit (this car has had this code since the day I've owned it so I think it is unrelated. Second code: 17953 Throttle Valve Controller: Malfunction. I also noticed while cranking the car over and trying to start it was making boost (1/2lbs) It also keeps holding boost (~1lb) even when I'm done cranking and the ignition is off. Thinking it might be diverter valve related?

[walky_talky20]

No. The diverter valve will absolutely have nothing to do with a no-start or a stall condition.

The throttle valve controller fault could be your problem though. That is basically what controls the idle. It should still be able to start, though.

Your first code (timing open circuit) means that the 15 amp fuse next to the ECU is blown. Not critical for running, but the VVT adds a small amount of torque on the bottom end.

I would proceed as follows:
- Clear codes and do a throttle body adaptation (TBA).
- Check for spark and fuel delivery to the cylinders.

[S-lime]

So I replaced the diverter valve, disconnected and recconected the ECU, cleaned the throttle body and throttle body sensors and checked the fuel at the fuel rail. All is working. I will try the TBA next. Any other suggestions?

[S-lime]

I also noticed the EPC light is lit up while cranking. Is this of any concern?

[walky_talky20]

Do you have spark?

EPC light is usually a fault with the Drive-By-Wire system (ie: pedal or throttle body), or a problem with the crank sensor (aka: engine speed sensor).

I can't remember for sure if it's normal for it to be on during cranking. Since mine always starts, lol. (ok, not funny. I'm sorry).

[S-lime]

I haven't checked for spark yet. Replaced the engine speed sensor as I had a spare, also did the throttle body adaption. Still nothing.

[Wrath And Tears]

If your car is making boost while cranking there is something seriously wrong with it. Our cars, when healthy, pull down at least 3 inHG vacuum during cranking. Not too sure what exactly would cause you to make boost while cranking. All I can think is your throttle body died and the plate is staying shut while cranking. It's almost a 100% guarantee that if your throttle body is setting codes it's dead or on its way out.

[WESLIFE]

Can you please check all of your fuses, then report back. Thank you!

[S-lime]

You are right wrath. I unplugged my intake hose and watched my thottle body while trying to start. It is not opening at all, it's staying completely closed. I unplugged the wiring going to it, 1 out of six wires had power. So it is getting power. What is my next step? New throttle body?

[S-lime]

Please help! I replaced the throttle body and it still wont start!:( Throwing 17953: Throttle Valve Controller: Malfunction still.. What do I do? I left the key on in ACC for 3 minutes to allow the throttle body to align. I need this car for work and I am starting to lose hope..

[Wrath And Tears]

http://wiki.ross-tech.com/wiki/index...3/P1545/005445

That's what ross tech has to say. I'd follow those steps and try to do a TBA with vagcom.

[S-lime]

Attempting it tomorrow. I have vcds-lite so I need to find someone with a registered version.

[walky_talky20]

I've seen a faulty ECU throw throttle body malfunction codes before. The circuit that drives the e-throttle burnt out of it or something. This was on a 2.8 DBW. Plugged in new throttle body, code would not clear. Put that bugger back in the box and returned it. Then changed ECU.

[S-lime]

Hmm.... This is the second ECU I've put in this car. Don't think it would have failed again?

[walky_talky20]

I don't know. How did the first one fail?

[S-lime]

Previous owner did a bunch of messing around with some program trying to chip it himself. Is there any way to do a throttle body adaption without a registered version of VCDS?

[S-lime]

Just noticed it is not showing any RPM while attempting to start. Tach is staying at 0. I replaced the crank position sensor again with no luck. Still only showing the throttle body code.. WHAT IS GOING ON

[S-lime]

UPDATE: Noticed I had low voltage at the throttle body, 5v instead of 12v. Traced it back to Relay 30 (ECU). Has a dry solder on it. Attempting to fix. Will report back.

[S-lime]

UPDATE: FIXED! It was the relay #30. It had a bad connection and was not supplying proper power to the throttle body!

[Wrath And Tears]

Awesome man! Good job diagnosing the issue, glad the car is fixed.