Ok, heres the deal, I have a '98 GXE auto, and whenever I let my engine idle to let it warm up a little, the engine runs/idles smoothly. But when I give it some gas (rev it to around 1800rpm), the engine does not run smoothly, like i could hear the engine go up and down, and the RPM needle bouncing a little. And this is all when the transmission is in park and the engine is cold. So I'm wondering, what the heck is wrong with my engine? If anyone knows, please help me out. Thanks.

 

what octane gas are you using? have you had the car since new? Does it still do it when it is warmed up? More info please.

 

I fill up with 92 octane Shells gas everytime. Yep, had the car since the very beginning, original owner. Engine acting funny only when its cold, like when I start it in the morning or if I haven't driven it for like 4 or 5 hours. Just beginning to have this problem, dont really recall it doing this in the past. Right now I have about 31,000 miles. No engine/exhaust mods. Using Mobil 1 synthetic blend and OEM Nissan oil filter.

 

Maybe it's your fuel filter. Try changing that. You should change it every 15K miles or so. I recently changed mine after 60K miles The slight hesitation below 2K rpm is now gone, and my top end is much stronger now.

Also, I put in a 300ZX fuel filter, so I can go 30K miles until the next time. The filter is a really hard to get at if you have ABS.

Look at this thread here and scroll to the fuel filter part;
http://forums.maxima.org/showthread.php?threadid=45742

Good luck

DW