[A4] Engine cut-out, spikey idle and other weirdness...

[Tyson Varosyan]

Hi Guys,

 

I bought my 98 A4Q 2.8 30V about a month ago. Today was the first time that
I took the plastic covers off the engine bay and this is why: 

 

Driving back from my dad's house the car just suddenly started acting out.
Cruising along at 3000 RPM the engine would just cut out. The dash lights
didn't light up or anything (as they would in an electrical power loss), all
electrical gizmos continued working, etc. It did not feel like losing a
single cylinder - it felt more like hitting the rev limiter - just total
ignition cut that jerked the car pretty noticeably. It would only last for
about a second and then everything would be OK again. It did this a few
times until I pulled over at a gas station and popped the hood. 

 

Idling there for some time the idle suddenly started jumping around - jumped
to about 1500 on its own, then almost died, then jumped again. Then the
engine just cut out and died altogether. I popped off the covers, reseated
the plugs around the intake - a 3-pin, which I assume is the TPS and another
2-pin, which looked like an idle controller. 

 

Then started the car back up and drove on. The problems continued to happen
about once a minute or so, mostly under cruise and light acceleration. It
died again at a light. Then after some time (maybe 10 minutes) the problems
went away completely.

 

I have noticed that a dirty MAS seems to be a common problem on these cars
and this sounds totally like something that a MAS would cause. If there is
another sensor in the system that can make the ECU cut all ignition, that
might be it too. It feels like a deliberate ignition cut by the ECU, but I
am not sure why...

 

#1 Where is the MAS?

#2 What should I use to clean it?

#3 Just for curiosity - is this car drive-by-wire (where the ECU opens and
closes the throttle plate based on a sensor attached to the gas pedal) or
does it still have a physical cable connecting the gas pedal to the throttle
plate?

 

Any other ideas, suggestions are welcome. 

 

 

Tyson Varosyan
Technical Manager, Uptime Technical Solutions LLC.
tyson at up-times.com
 
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