"Gum on the tips of the injectors changes the fuel spray pattern from the desired cone-shaped mist to an off-centre stream of fuel. When fuel is injected in a stream, it tends to drop out of the air stream or takes longer to evaporate in the cylinder. Either way, the fuel doesn’t burn properly and a driveability problem results."

http://www.canadiandriver.com/2001/04/21/a...or-cleaning.htm

Octane booster help you reduce chance of knock on a hot day + high boost

 

I'm gonna try re-wiring the fuel pump directly to the battery. There's a diy in here somewhere I read earlier. I noticed the fuel pump hums changes tone under different voltage conditions (eg fans coming on, tops going up/down and windows). These conditions also futher perturb the leaning condition at idle and I'm lead to think that its either ignition or fuel pump not receiving enough constant voltage. Because its returnless with in-tank regulater, not sure if this is a factor in delivering fuel. I have noticed a big difference in fuel pump hum (quieter) compared to another members boosted s with the same fuel pump but its a non-returnless. Unfortunately I didn't get to test his voltage before he sold the car. The car idles perfect and af perfect when cold. Bring it around the block and that all changes. And also change the ngk's out for the denso IK24's tomorrow. Thanks for all your help guys. Hopefully this sheds some light with boosted returnless systems experiencing this issue. Last thing I may have to do is convert to a return fuel system.. =)

 

What plugs are in it now? Stay away from non resistor plugs and if thats whats in it, thats probably your problem.

Read this....
http://www.ngksparkplugs.com/techinfo/spar...faqresistor.asp

Also, I've heard numerous bad things about the Denso iridiums breaking tips off into the engine. Be very careful. You should look into the NGK BKR8EIX iridiums, stock number 2668. They are much better IMO.

 

Nevermind, I just saw that you had the BKR8EIX's in the car. This is weird then. Maybe just a bad coil or spark plug?

 

Completed the fuel pump re-wire to battery, switched out the ngk bkr8eix for the denso IK24's and repositioned my AIT sensor. Checkengine light no longer comes on and the high rpm breakup is 90% gone!

The car drives much smoother now, however its still a little lean at idle. I could definitely tell the difference in the fuel pump re-wire, more consistent af's too. The spark plugs made no noticeable difference, imo. And moving that AIT to the cold side of the intercooler also helped. Before it was on the hot side, dont ask me why.. I am using the AEM AIT btw, not stock.

I'm much happier with how the car drives and responds now. Time for a retune. Thanks for the help guys.

 

14% isn't enough to be that rich. Should be about 35% before you start adding fuel from stoich. So your running too lean at idle and too rich at partial throttle/closed loop. That might be enough to cause your issue.