forum.audiv8.com Foren English Audi V8 Forum Energine go up and down in rpm "somtimes"

the motor 4,2 start fine and run fine, but somtimes and now offen. begin the energine go up and down in rpm and i shall give 1/2 to full gas for at the car can acc. normaly.
But when i go under 1/2 gas its begin again. what can be wrong ??
i have one time stop the energine for 30secunds and when i start again the problems where gone

The car have Euro cat 2 install and i have the idea at its this black box ther couse the problems but i dont know, can i cancel the euro cat 2 ? for testing this ?
the cat warning lamp has ligting 2 times for a few secunds but i dont think its the cat ther is gone. becouse its normaly dont light when the problemes come and normaly run my cars fine without any problems.
Sorry my bad english, hope some one can help me to locate the problems.

Regards
Sören

Hi. It can be problem with that black box you mention, that actually main air valve (small electro motor for adjusting the running of the engine). It’s can block sometime. But also, and most likely it can be problem with Lambda sensor, and I suggest you to check that. The car comp should show error of Lambda sensor. You can disconnect it, reset error in comp (and car should then run on secondary program). If that fix your problem, then it’s Lambda sensor. And you can drive your car on secondary problem as well.
Best regards...