Miss fire at low RPM while coasting

[blazen_accord]

I have traded by NGK iridum plug for plain NKG copper plug on my swap JDM F22A engine and don't know if it have to do with it or not. I get missfire/backfire when I let off the gas anywhere below 3000rpm, I get that pop, pop sound from my exhaust. it only do it after I let off the gas. Friends told me maybe i'm running a bit to rich at below 3000RPM, so i adjust my SAFC down from -35% to -39% accross 1000-2000-3000 rpm range for low throttle. But I still hear the poping noise from the exhaust, what could be causing it??

Also Around 2000rpm if I let go of the gas petal and coast down before comming to a stop, the the rev will slower go down like it should and then surge up and down from 1200rpm to 1500rpm. if I hit the brake the rpm will go down and idle normally around 750rpm-650rpm. I just replace my alternator because it was bad, but that did not help with both of my issue.. any suggestion?? possible my distributor is dying?? I got new OEM cap, wire and rotor replace 4 month ago.

[hemlockz]

good question, mine does the same thing.

[hemlockz]

I have a F22a1, shortram, delta cam, and straight through muffler. 140k miles. Timing is at a tick above the highest timing mark, so probably 18-19 dbtdc. Cam timing is 1 or 2 degrees advanced. I have had a rich idle since putting in the cam. I always had popping sounds when decelerating, (especially in 2nd) and a loud exhausted tone, but recently the tone has become a harsh noise and insanely naisly below 3000 rpm, it sounds a bit constricted and the noise seems to be coming from under the car at the resonator before the muffler. Coasting down, it sounds like an airplane flying through a long tunnel while misfiring here and there, (sort of like a flange sound effect) but I haven't experienced any noticable power loss. The overall change in noise happened this weekend after driving 50 miles, I came to stop and noticed something different. Where it used to sound not bad, now it's annoying... like a spree scooter on crack.

[Fearit22]

Mine has done that ever since I put on my test pipe. I guess it's normal? My car still runs well though.

[WhiteGhost]

Sometimes a Exhaust leak will cause that

[19dabeast85]

It's normal on any vehicle while decelerating in gear, stock exhaust muffles it, your aftermarket exhaust amplifies it to where you hear it. Absolutely nothing to worry about.

[WhiteGhost]

Yeah....When you let off the t.b flap closes and the car shoots lean.....And the spark burns the rest of the fuel

[Cblove]

The two above posts says it all, if you happen to be running cat less that will do it also with a modified exaust. Just unburnt fuel, not a misfire. Don't worry man.

[wed3k]

just keep checking your spark plugs..why is the ignition timing at 18?