vibration at ~700rpm
 

I have an base 86 with an auto tranny. The problem that I have been having is that my transmission/engine (don't know which one) vibrates when the car is idling at around 700 rpms when I put the car in reverse or drive. This is the ONLY time that the transmission/engine vibrates. I'm pretty sure that it's not the u-joints because I had the whole driveshaft replaced with Mazdatrix's aftermarket driveshaft.

I have done a search and I've assumed four things.
1. Loose radiator fan
2. Transmission mount
3. Engine mount
4. vacume leak
The only difference is that the symptoms are a bit different from what I am experiencing.

Any idea's on what causing this?

Thanks

bump?

i thought the idle would need to be 750-850 rpms... or at least mine has to be because i have some stuff done to my car... if its not at idle in N then i doubt its your motor mounts, but if it is doing it in gear only then possibly its your tranny mount... they break on our cars alot or at least everybody i know, i have replaced a lot of them on my friends cars

my car is a standard. my car idles around 750-800 without the engine struggling but the whole engine shakes like hell. I have just come to accept it unfortunatly. I know my passenger side engine mount is partialy bad but still holding on.

My theory is. these engines are suppose to run smooth any day. engine mounts are just to hold the engine and cushin the movment durring acceleration or very slight vibration at idle. So something has to be forcing the engine to shake. I dont know if this is the same as yours bout thought i would throw it out there.

Justin