Idles rough in reverse gear

Hello,
It is an automatic 1996 G20 , 90K miles...I had just recently tuned it up....changed everything (filters, spark plugs, wires, cap and rotor)...the transmission fluid also has been flushed and the filter replaced...I brought it to a transmission shop, and they've told me the transmission is good...
I've just noticed that when the car engages in reverse it idles very rough, however drives fine. I don' think it did that before. Does anybody know what could cause the rough idle in reverse? It idles fine in other gears.
Thanks in advance!
Regards,
Viktor

It feels like the car with a manual tranny about to stall, because the clutch pedal is not pressed, except it doesn't stall and the idle stays steady.
Thanks!

Check your engine mounts in case the rough idle is really the engine shaking around on broken mount/s.

This is a real longshot but ... try pulling the reversing lights fuse and see if your problem still exists. If it goes away, you may have a short between that circuit and something else like ignition circuits etc.

Thanks for the info...I have a question though...If the engine mounts are bad, wouldn't it vibrate the whole time? And, what causes the mounts to go bad? 90 K miles - isn't kind of early?
Thanks in advance!
Regards, Viktor

I don't know if it has anything to do with it but I forgot to mention...the car battery seems to be in bad shape...It had a lot of build up on it and I cleaned but...Could the battery cause this? It seems like it started to shake in reverse after I tuned the car up...Here is what I replaced:
1. PCV valve;
2. Fuel filter;
3. Wires - NGK;
4. Plugs - NGK;
5. Distributor cap;
6. Distributor rotor;
7. Air filter;
8. Oil filter with oil change +Slick50;
9. Valvoline SynPower Fuel system treatment;
10. Cleaned the battery terminals...
Any ideas????

Originally posted by vikon
Thanks for the info...I have a question though...If the engine mounts are bad, wouldn't it vibrate the whole time? And, what causes the mounts to go bad? 90 K miles - isn't kind of early?
Thanks in advance!
Regards, Viktor I suggested engine mounts because when in reverse the axles apply a torque to the engine/tranny in the opposite direction - so the engine mounts will be loaded differently.

I don't see anything in your list that is likely to have caused this. I'll have a look through my Haynes manual after work and get back to you.
Originally posted by vikon It feels like the car with a manual tranny about to stall, because the clutch pedal is not pressed, except it doesn't stall and the idle stays steady.Do you mean it lurches when you are reversing like a person trying to learn how to drive a stick? Is the idle problem only when you are moving in reverse or when stationary with reverse selected?

the same kind of vibration...the RPM stays steady though and the engine doesn't stall...
you can feel the vibration mostly when stationary with reverse selected, and it eases out when you start moving, so I guess I can say that it vibrates only when stationary...
I had a transmission guy looking at it this morning, and he said that it's an engine mount, and it's nothing to be concerned about unless it goes really bad...So I guess it has nothing to do with the idle itself...
Thanks for your reply!
Regards,
Viktor

Once one mount fails the others have to take up the extra strain and eventually they may all fail. Also if your engine is moving around more than it should it may be stressing other things like your exhaust system etc. Also I've heard that the transmission casings are prone to cracking even with good mounts so ...

It definitely isn't anything to panick about, but still, it just ain't right.:) Glad it wasn't anything more serious.

How much would it cost approximately to replace a mount? I know that the part itself isn't cheap ($50-$150)...It must be a lot of labor on top of that...Any ideas?
Thanks!

My Haynes manual only mentions 4 mounts. One on the pulley end of the motor, one at the rear of the engine/transmission, one on the front of the engine and one on the tranny. If you have a good look around you'll find them but you might need to get underneath to see them.

Look for black liquid leaking from them or torn rubber. Check also that the bracket bolts haven't worked themselves loose

No idea on replacement costs. A good one from the junkyard might be a better cheaper option. You'd be very unlucky if you had to replace all three.

Labour is not much compared to some things but if your handy you could do it yourself.

It really isn't an urgent problem though so take your time.

:D Thanks so much for your input!!! I'm so glad I found this forum...I've been posting my questions on a newsgroup previously (alt.autos.nissan), and I haven't had a good experience with it. I also have a 1987 Nissan Pulsar NX, and have posted questions about that car...Basically, no input on neither of these cars..
Thanks again!
Regards,
Viktor

Vikon,
Check out this related thread:
http://www.automotiveforums.com/vbulletin/t7712.html