i apologize in advance for this long post, but i wanna be as detailed as possible so that you guys might better be able to get a grasp of the whole picture.

i have the following mods.... Z-tube, Popcharger, Motordyne 3/8" plenum spacer, TopSpeed headers, Crawford high flow cats, Fujitsubo Y-pipe, and Fujitsubo Legalis-R exhaust

the Z-tube and Popcharger were installed with roughly 1200 miles on the car.... odometer now reads at 20k and change. on very rare occasions over the past 6 months or so (once every 4-6 weeks if i had to put a number on it) when idling at a light, the motor would feel "jerky" is the best way i can describe it.... the idle was lumpy, like it was about to stall. you could feel the entire car shuddering alittle. since this was always at idle or just when easing onto the gas, i attributed it to a crappy 5AT.

like i said, this problem was random and VERY rare, so i never really took note of it as a serious problem. also for the past month or so, the car was throwing a CEL, which read a lean condition on bank 1. i finally tracked that culprit down... my plenum bolts needed to be retorqued. did that, reset the ECU, no more CEL. that was about a week ago.

this past weekend, we put the car on the Dyno Dynamics at MRC Motorsports. the car turned a 247.3 (another 5AT pulled same number with just intake and a borla exhaust... which is weird). while she was on the dyno, after Julian let off the gas, you could hear tons of backfiring and gurgling coming from the pipes. ever since the dyno run, the shuddering, "like i'm gonna stall feeling" happens every time the car is idling.

so i thought to myself, maybe the motor's not getting enough air at idle? checked my popcharger.... thing is filthy. so, i went thru the whole cleaning process today. cleaned, rinsed, re-oiled, let dry a long time. i briefly started the car (like 30 seconds) without the Popcharger filter attached, and it seemed to idle fine. after re-installing the filter, the problem returns.

once you get going, she runs fine and feels just as strong as usual. however, the lumpy idle is there, it hesitates slightly when you ease onto the gas, and the idle is lower than i feel it should be (it hovers right around 600rpm right now)

so.... any thoughts?

my car is in the midst of a full ECU reset right now, so maybe tomorrow morning when i reconnect it will be better. if not, my next step is gonna be to 86 the whole popcharger filter element and overnight a new one from JWT, but i'd rather not spend the $65 on a new one if it's a simple problem that i'm just missing. thanks in advance for any insights you guys might have

 

have yoiu checked the MAF? sounds like it may possibly heading south. any leaks around the intake?

 

Do you have a grounding kit? That will help with a rough idle on a 5AT.

 

sounds like an intake leak...is everything hooked up tight and plenum stuff bolted in tightly

 

praying that it's not the MAF since i don't wanna replace it. no air leaks around the intake that i can find. i cleaned and re-oiled my Popcharger intake to make sure that wasn't the problem (and no, i didn't use too much oil b/c i know that can taint the MAF)

yes i have a full 10 wire grounding kit from GroundingGear. and trust me, this kinda rough idle is WAY beyond what a grounding kit can fix. it idles like a Peterbilt tractor-trailer. it's actually audible if you start the car and then go stand outside it.... you car hear it in the exhaust pipes that it's not running right, sounds like it's gonna stall any second

yes when the problem started i checked everything. i thought since the car was running lean it might have been a leak post-MAF, making the car pull in unmetered air. all connections for Z-tube are tight and i retorqued the plenum bolts to Motordyne's specs.

i've been thru 2 ECU resets in the past week, the rough idle persists. and although the reset killed the check engine light, the car wouldn't pass inspection this morning b/c the "emissions control system" is not ready to be tested so soon after an ECU reset. the guy told me to drive 100-150 miles, although i guarantee the CEL will come back at that time

 

I doubt it's the MAF. I had a Nissan MAF go on me on my 03 Alti, and it was not as he's describing. My car felt like it was running on 2 cylinders, and would run ok as long as VERY little throttle was applied. A little more throttle and the car choked as it was going to cut off.

 

yea in that case i would say also that it's not the MAF... b/c at anything above idle the car runs absolutely fine... pulls hard from 1000rpm all the way up to redline

 

steve, you might want to tune the engine. i'm putting my headers and exhaust at mrc on the 29th and am planning on putting in the UTEC. my MAF failed on me in november and the dealer helped me out under warranty, it's $700 dollars to replace that thing, i found out that it got contaminated cause i didn't replace the lil filter on my injen intake. not the main filter, it was the lil one. ask julian cause it sounds like you need to tune the car to the mods.
good luck. tony

 

Do the exhaust leak checks with the stethoscope.

Also check to see if a piece if plenum gasket isn't bent and folded over upon itself.

 

havent done a listening check b/c i don't have ready access to a lift. i have been avoiding the headers as an explanation b/c i SURE don't want to re-do that whole thing

one thing to note, the problem is less severe at night (when it's cooler). also, turning the A/C on and off has no effect on the idle RPM. it stays between 600 and 650.

i knew the topspeed headers weren't going to last forever for their price, but i was hoping they'd survive long enough till i go FI. i guess we'll find out

also, about the plenum spacer...i have one of the original ones that uses the metal standoffs in the middle and the foam gasket tape... if i remove the plenum is there any risk of the standoffs falling into one of the intake runners?

 

SI, let us know the culprit, I am very interested in this thread as I will have similar setup as you, except cat back. I bought topspeed headers too...i really hope that is not the culprit, or I'll hate myself for not going strup or crawford.

 

i think my MAF is fine b/c the car pulls hard from 1000rpm right up to the redline. if my MAF was going south the motor would be running alot worse than it is.

there are literally dozens of cars with modifications almost exactly the same as mine. could my car benefit in horsepower with a tune? sure. but with this combination of mods, the car shouldn't be running this bad... something is definitely wrong.

i'm starting to lean toward's Hydrazine's possible explanation that the headers may be the culprit. there is a difference in sound that i've noticed, more hollow than before. and when i'm driving past retaining walls or big trucks (something that reflects the sound back at me) i can hear a faint hiss. i guess i need to wait for a lift to find out.

 

topspeed quality is very good, just as good as other nismo copies such as strup. The problems you describe don't really sound like broken headers or a header leak or whatnot.

edit: fyi, if it were a header leak (since you wroet above about a faint hiss) you'd know - you'd have a VERY noticeable 'tic tic tic tic tic' at idle, amoung other issues.

 

it could be a cracked header? if it sounds like a mac truck that could be the problem. let us know.

 

Try removing Popcharger filter again (longer than 30 secs) and see if idle is stable.