Hi,

When I reach 1900/2000 rpm with my A8, the whole car shakes violently and it goes away if I let go the gas pedal (lower rpm) or if I press more on the gas (to gain higher rpm). This used to be present before with my old faulty transmission (dead 4th and 5th gear) and it's still present even with my ''new'' transmission (good used 50k tranny). I thought it was part of the transmission or torque converter that was broken, but the problem is still there...

anyone experienced this?

My thoughts are mayyybee:

problem with torque converter lock-up OR problem with some of the drive shaft joints ..


anyhelp, thanks

 

I've read about it only in early A8's (pre-facelift 97-99). Torque converter clutch locking and unlocking ("hunting") and only at 2000 rpm and lower. Some cases, the problem was with the TCC valve in the transmission valve body and others were with a faulty TCU sending random signals at 2000 rpm and less. The problem all in cases was gone above 2000 rpms...something changes with valving there, due to signal from transmission speed sensor (direct relation to engine rpm).
You have different transmissions, but probably the same TCU...doesn't mean that's your problem, but.....................

 

Allright thanks,

I'l try with another TCM and keep you guys posted

 

Fixed it !

I had a bad ICM (car was running on 7 cylinders), changed it today with a brand new unit, now runs smooth on all 8 and the transmission problem is gone. Don't know how it was related, but i'm just happy it's solved.

 

Geez you didn't know what a misfire felt like? Oh well, now you know.

 

I know what a misfire feels like and I knew it was there, but at 2000rpm it was muchhhhh more violent than a misfire. it was almost exactly as if I had a loose front wheel and about to lose it

 

A dead cylinder (like in a bad coil or ICM) is a very violent event compared to a random misfire. I had almost forgotten the older A8's had external power output stages, glad you got it fixed.

 

Yep the 32V's have 2 ICM's w/POS's..one for each bank. The 40V's have POS's built into all 8 coils.

I had a single coil go (#8) suddenly one day on the way to work and truly believed it was the trans going...violent shaking at low rpms & mostly smooth at high (didn't think of that when Martin said his idle was OK...mine was really bad). The flashing CEL light and horrible idle in neutral at the next traffic light gave me a glimmer of hope that it WASN'T the trans.
I called my wife to bring my code reader with her, when she came in....we work together...talk about "infinite patience", huh? I was really tickled to read a #8 misfire code, esp when I switched the coil with the next cylinder and got a new #7 misfire code.....whew!....$35-40 five minute fix w/10mm socket.