So my rx8 is not throwing any codes other than running lean, I know this because it backfires often I have a video of this and it has been going on for a while. I have a short ram intake, that’s the only performance mod, I’ve tried to clean it and the maf sensor and everything, could my intake really cause it? Lmk your guys opinions, don’t want to further damage my car.

 

Remove the short ram intake garbage. It's both a power downgrade and a reliability problem because it can mess with the MAF measurement.

Backfiring is running rich, not lean. If your car thinks it's lean, adds fuel, and actually ends up rich, you have an AFR measurement problem as well, though normally the O2 sensor should pop codes if it's busted.

It's also possible you have ignition coils and spark plugs wires in the wrong order so combustion happens out of time. Check that and the intake first.

 

I just put new coils and plugs, wow what a difference, I’ve been driving in what they call limp mode, night and day in speed and acceleration pulls a lot better but that is as about 2 weeks ago so ignition checks out, also starts much faster. Put the old intake back on with a new k&N filter. Also cleaned the throttle body and maf sensor. Still getting the code but now I got a CEL, which means it’s bad enough to trigger that light. What do I do next, I don’t really wanna take it to a mechanic if I can do it myself, should I get a new oxygen sensor?

 

What is the CEL code? That'll be a clue.

 

Yeah same code as before P0171

System too lean Bank 1

what should I troubleshoot next. Ignition was replaced 2 weeks ago, night and day difference, was running in limp mode before, also fixed the whole car shaking in 5th and 6th gear.

put old stock air box in cleaned throttle body and maf sensor, (it doesn’t idle as rough)

could it be the o2 sensor? Vacuum leak? And how would I check for one? Thanks

 

Could be a vacuum leak for sure. If you can get it to idle, what are the short and long-term fuel trims, AFR, and MAF airflow g/sec while idling and fully warned up? I don't really think it's the O2 sensor, it would have thrown its own codes if it was.

Are the vacuum hoses routed correctly?

 

yeah vacuum hoses routed correctly. I don’t believe it’s the O2 sensor. Disconnected and reconnected the battery to reset the ecu, damn did it struggle to start, died a couple times, couldn’t hold an idle, but once it adjusted it was good, fine, cold and hot start, but I’m guessing it’s working hard to keep a good A/F ratio but still struggling throwing that lean code. Here’s a video of me slightly revving it at idle and then letting it drop, when it drops it drops to like 500 rpm’s and flutters, then pops back up. Idk what else to do. I can’t check the A/F ratio from my obd2 but I will and can check the masa air flow rate. Anyways lmk what you think, thanks for the help so far.

 

yeah here’s the video of the fluttering idle.

 

Fluttering idle.

 

Why can't you check AFR from your OBD tool? It should be easily accessible just like MAF rate. If there's a vacuum leak you'll see warm idle MAF rate below 5 grams/sec at 800rpm, and the fuel trims should be high, up to 25. For it to trip "running lean" more than 25% of air going into the engine is coming from somewhere other than the intake, which is a lot.

 

I have the blue driver obd2 and it doesn’t show up as an option, I think it’s a vacuum leak, it’ll be a pain in the *** to find tho. If it’s not that, would it be a fuel problem? Fuel pump, fuel injector? But yeah, from the symptoms pretty sure it’s vacuum leak, any areas I should look for that are prone to vacuum leaks, the intake is all good I’ve checked it.

 

AFR might also be called equivalence ratio or lambda, depending on what software you're using. It's gotta be in there ..
What about fuel trims? LTFT and STFT?

Commonly overlooked vac leaks: VFAD nipple under the throttle body that you can't see; oil injector vacuum box under the UIM..

 

My money is on vacuum leak.

Listen to Loki he is wise in the ways of the force

 

yup it was the Vfad nipple completely off of it. Fixed it, reset ecu aka disconnected battery, still backfires and pops a bit on deceleration, is that still normal? Or should I just wait until the ecu adjusts.

 

Wait for it to settle on new trims, and it might have trouble idling until it learns. In a couple of drive cycles should be OK. May want to check the fuel trims again then, in case there's still a smaller issue.

Popping and backfires shouldn't really happen, but it's a matter of degrees. Is the exhaust all stock? The risk with backfires is you damage the catalytic converter (which ought to be checked for crumbling anyway if unknown condition)

 

yeah unfortunately can’t check fuel trims no data pops up from my obd2. Exhaust is stock, and now sadly, so is the intake, shouldn’t have wasted $200 on a aftermarket one. It still backfires, and has like a backfire hiccup if I’m revving in neutral at 6.5k, ssv needs to be changed soon too, as it’s been ticking at idle. Don’t know, considering possibly gutting my cat if it’s going bad tbh, but it doesn’t glow red even after pushing it and it being hot, I’ve checked.

 

so yeah it runs fine ssv ticks at idle still possess me off but it has a fairly rough idle which I know is normal ish for an rx8 but if it’s warmed up and specificcally in neutral it has this sort of thumping intermittent, that I can feel underneath my seat and it’s quite annoying, could that be exhaust related, possible back pressure?

 

You shouldn't feel any thumping, especially at idle. Slight vibration through the shifter maybe, but nothing thumping. It's not supposed to be rough either.

Thinking maybe you have a spark plug loose? Does the thumping hit in time with engine?

 

damn yeah idk why, wdym my hit in time with engine?

 

I mean does the frequency of the thumping increase with engine rpm, or with vehicle speed? Does it happen at stationary idle?

 

only at idle in neutral

 

The knocking might be a broken engine mount. Somewhat common, but wasy to check, there's a mount in either front wheel well. Usually the right side one is worse off because of proximity to hot exhaust.

 

sadly? Dude the stock air box on the rx-8 is superior to the hot air intake crap you got rid of, be happy you got rid of that.

 

yeah, definitely a hard pill to swallow after paying like $200 for it, definitely had a nice loud sound to it but tbh, yeah it’s better now, doesn’t backfire or any stupid ****, running like it should be, just regret spending money on it.