I want to create a gapless audio CD in Foobar, I've tried adding the gap killer in dsp manager and ticked "Use DSP", "Use ReplayGain", and "Don't reset DSP between tracks" under the Audio CD Writer option in Foobar, but still when I listen to the CD I created it still has about a second gap between the transition of each track. How do I go about this? BTW my source is a WAV file extracted from an mp3 file using Foobar.

Thanks so much guys and regards.

A WAV file extracted from MP3 using foobar2000 should already be gapless.
Since version 0.7, foobar2000 has implemented gapless MP3 decoding, but it only works with recent LAME.exe-encoded MP3 (3.90 and up).
If this is the case, then you should disable Gap Killer as it may be introducing artifacts by "cutting" an already gapless track.

If this IS NOT the case (your MP3 where encoded with something else), I recommend fixing them. Read this thread for a good explanation on how to do this.
I recommend to go this way because you will fix your MP3 files for good and it will save you from some headaches in the future.

Once fixed, decode MP3 using foobar2000's diskwriter component and burn the resulting WAVs with burning software of choice.
This is the way I do it, and so far I have got nothing but perfect results.

What if I extracted the WAV file from an mp4/aac file? wherein the mp4 was originally transcoded from an mp3 file? Thanks so much for the quick reply

Then you are screwed, I guess.
AFAIK the only AAC implementation that supports gapless playback (I don't know decoding) is the Nero one.
But still, the gapless information went down the drain during the transcoding (dumb idea, if you ask me).

Although, you can try trimming the WAV file with an audio editor.
This seldom works, but still, it's better than nothing.