I swapped in a 7mgte into my NA a few months ago, and now its developed a rev problem. When I rev the engine up and hold it steady without being in gear the engine will rev to where I want it to, stay at that rpm for a second then drop down to 1000 rpm, then back up. The rpms keep fluctuating up and down. The idle seems to be ok. The fluctuation just happens when I rev the engine and try to hold it steady. Any ideas?