Please help, stumped.

I posted a thread yesterday haven't got any replies. I have a 95 nissan sentra with a 1.6 liter dohc engine. The check engine light not on, self diagnostics is giving code 55 which means everything checks ok.

When going down the road(not accelerating), coasting, the rpms will rise and drop on their own, for example, If I reach the speed limit and let off the gas to coast the rpms will fall to about 1300, rise to 1800, back and forth back and forth, I don't understand why it's not staying steady. I haven't noticed any problems with the car in park idling, just going down the road it does that. Other than that it drives great, please, any suggestions.

Any ideas???

my first guess would be a transmission problem. sounds like it cant decide what gear to stay in.

Thanks for your reply but it's not switching gears when it does this.

it might not be switching gears, it might be slipping all together. my step dads trucks trany slips and the rpm jumps, try replacing the filter in trans fluid that is what he did and it stopped for about a week, then it started again we pulled it and took it to a shop and they told him it was trashed that every thing needed to me replaced, so we just went to the junk yard and pulled one and stock it in.

I'm sry I forgot to post back, the throttle cable got outta adjustment, I noticed when I looked under the hood with the engine off that the throttle was pulled up a little bit by the cable, I readjusted it and tightened the cable back down good and tight and it's running perfect now, thanks for the replies.