Mystery Audi Diagnosis

[anabolice30]

So recently my 1999 audi a4 quattro 2.8 had problems starting up when the engine was warm. Cold starts were no problem. I replaced the coolant temperature sensor, which is what all signs seemed to point to. I couldn't get the new sensor all the way in because I'm a dumbass and didn't take out the old o-ring. So I tried to use silicone to seal it. I let the silicone dry for about 18 hours and my car started with no problems. Then the idle went up to about 1400 for a couple seconds, then back to 800 like normal. After this I drove my car around the cul-de-sac and parked it, then I went inside for the night. The next morning I have to move the car so Comcast can do some work in my yard.

I start the car and it dies immediately. I start it again with no problems and rev the engine to keep it alive. It is jerking and cutting out and not going above 10mph. I get it in my driveway out of the way of Comcast and take a look at the sensor. I pull it out and reach my finger into the coolant pipe and think "maybe the old o-ring is still in there". Sure enough it was. I pull it out, put the new sensor in which now fits snugly. Car is still still driving like shit. I drove it around again just now and the sensor came out and there is coolant all over my engine. Not sure what the hell happened.

Any ideas guys?

[Exodus_2pt0]

Does you forget the plastic clip that holds the sensor in place?

Your cooling system is under pressure at operating temperature, that's how it keeps the water from boiling. Without that tab the sensor will not stay in.

As for the running issue, make sure you didn't crack any vacuum lines, which it sounds like you did. Or something is off, brake booster hose maybe?

You can also hook up a scan tool and check your short term fuel trims, if it is over 5% then you probably have a vacuum leak, and the ecm is adding fuel to compensate for extra air.

Find or buy a new clip for the sensor, and check all your hoses.


Here's a photo of the tab I'm talking about. I'm not positive on the 2.8 but yours should be similar. Ignore the arrows.

[anabolice30]

This is the only way I could get the clip on and it didn't seem to hold anything in place, but I will check again and check for vacuum leaks. Thanks.

[Exodus_2pt0]

You gotta take the clip off, push the sensor down into the housing, and then the clip goes through the slit in the side of the housing and holds the sensor in.

[anabolice30]

Awesome thanks! Got the clip in. Will search for vacuum leaks now.

Edit: put everything back in and now it will start, but dies.immediately. Can't even rev it to keep it alive..

Found this on the intake boot. Doesn't seem like it would cause a big enough vacuum leak to kill the car, but who knows.

[88BlackS-ETA]

Disconnect the MAF and see if it will run. On my A4 B6 the maf was so dirty that it killed the car immediately.

[anabolice30]

I will try that, but I doubt it's the MAF because this problem came on so suddenly, and it ran fine other than the startup issue until I switched this sensor.

Edit: unplugged the MAF ad nothing changed.

[anabolice30]

So I fired it up again today and this happened. I was flooring it but it really wasn't wanting to rev. Now I'm thinking maybe I have a misfire https://youtu.be/jm2ciflUi7E

After that I got the engine to stay on by holding tbe RPM around 1500 but the rpms were bouncing even though my foot was steady on the gas

https://youtu.be/U60IB4bbFe0

[anabolice30]

So I cleaned the MAF sensor. Didnt do anything, but that's sething to cross off the list. Took out my spark plugs and they all looked like this. I've never changed the plugs since I've owned the car for less than a year. Fortunately I have some NGK plugs handy.

[TimKninja]

cleaning the MAF sensor never does anything EVER. Unplug it, if it runs better, get a NEW (not junkyard, there will be plenty to coose from because Audis are fucking garbage) MAF sensor .

You ether have a vacuum leak, plugged fuel filter, plugged up injectors or a dying fuel pump. is there any codes?