i just noticed yestarday that my car idles at 900rpms and from time to time it with feel kinda rough and i notice that the tach is moving up and down (slighty) with the rough feel i have not done anything different with the car lately other then washed and waxed it and with this problem i also noticed that in first gear i only hit 12-14 pounds of boost then it starts to fall and in second i hit 15-18 and in third i hit 18-19. i don't really rember if this boost thing was going on before, i have a mbc, wired in parrell a forge 007dv, and im running the ngk plugs (the ones that a lot of people say are good for a chipped a4) i have a vag i get no codes but im not to good at working it nor really understanding what it is telling me (i just got it and only used it 3 times) most of my mods are listed below. the only thing that i have done was clean my k&n filter but it ran that much better after till this crap happened.

 

oh i forgot it is chipped but i have yet to figure out by who? i bought the cars used and it was already flashed that is an issue im still working on and help on these issues would be great

 

Check for vacuum hose leaks.

I wish I could be more specific but a rough idle could be a lot of different things; however, it also looks like you have a small boost leak which makes me think you have a leaky vacuum hose.

Also, log block 2 or 3 with VAG-COM to check the MAF. You may have gotten the MAF element oily when you cleaned your K&N if you were heavy handed with the filter oil.

And, I hope your MBC is run in parallel with the N75 not the Forge DV.

 

I've heard a bad CTS (Coolant Temp Sensor) can cause erratic idle... but I would imagine it would also throw a code...

Nice looking car BTW

 

That's true about the temp senor. Check to see if it's green. If it's not, go ahead and change it anyway. The old black ones are known to go bad.

 

thanks im not to sure what the mbc is hooked to it was on the car when i got it i asked my mechaniac about it and he said it was fine and that it is asking for the boost that the computer is wanting so i should leave it alone i do know that one of the hoses from the mbc goes to the n75 valve but the other i have never really looked where it goes


and thanks for the comment

 

where is the coolant sensor located?

 

It's loacted on the back of the engine between the fire wall and block. Near the top. Audiworld has write up on how to replace it.

 

found the write up does look to hard just might be missing some skin from my knuckles is there any other ideas??

 

Not sure from your post if you have it set up this way or not but you cannot have a MBC share the vac/boost reference with the diverter valve as it will likely cause boost control problems.