Idle surge after Stillen supercharger install -SOLVED
 

Hi Forum,

I'm having issues with idle after my S.C. Install. At startup in closed loop, idle is fine. After warmup and transitioning into open loop, the idle is terrible. Will go up to 1K RPM's and bounce around up to 1,500. I do see the fuel trims increasing.

The tuning shop went through a compression and leak down prior and numbers were good. 210 on average across the cylinders and leak down was less than 10%.

A boost and vaccum test was done and all is sound. MAFs were cleaned out and I also pulled the throttle bodies out and cleaned them (battery disconnected and unplugged the TB's before taking them out)

If I cap the PCV, the idle surge disappears, which would lead to a leak somewhere... But boost and vac test came back fine. I changed the PCV after that test and still nothing. I may have an exhaust leak between the drivers side manifold and high flow cat. Can an exhaust leak cause this idle surge with forced induction? I had a leak there before and I never had idle issues. I figure the supercharger has changed the dynamics and wanted to ask.

Some info:
07 350z Nismo @53k miles
Standard Stillen kit (no upgraded pulley, no fuel return, walbro 255 fuel pump with the regulator tapped with provided drill bit)
Kinetix HFC and a Tanabe Y pipe to factory OE Nismo exhaust
Probably irrelevant, but I also added a Mishimoto oil catch can(closed)
Has a custom tune (dyno'ed at 350wHP), idle set to 800rpms
1+ step colder plugs (370z spark plugs- standard gap)
Replaced Stillen provided BOV with a authentic HKS
Z1 oil pan spacer
34 row oil cooler

Never had any issues before, solid as a rock


Much appreciated,

-NT

There were a couple of threads that I read with slight idle surge at the set idle
RPM's. I believe this is not my case, the reason for my post.

Was able to get a couple runs today. A couple lights came on:

P0300 - random misfire
P0507 - power train idle control system RPM higher than expected

The past few days I was ruling out a few items. Vacuum was near perfect and no boost leaks. I may/do have an exhaust leak but I wouldn't think it would DRASTICALLY change the idle.

The issue is with the HKS SSQ BOV mentioned above. It's a BOV usually used in turbo applications and the spring rating is above 6 PSI for sure. Just recently learned that the BPV needs to be partially open with a centrifugal supercharger. This translates to using a BPV with a 1-1.5PSI spring rating OR using an adjustable BOV that can get down to that area. Made sense. S.C. is constantly running (unlike a turbo) and excess pressure needs to go somewhere.

Replaced the BPV with the Bosh one and ran an idle volume relearn and then viola! Problem solved.

-------- BUT -----------
As some have said... what a $h|itty design. The MAFs are soooo close to the filters that the moment the fans kick on, fuel trims start changing because of the air flow and temp change. Did they test these kits in a vacuum 0 gravity facility?

As other have done... they did away with them or created a better shield. I used the one they provided (350z HR single intake pipe dual MAFs) and it does 0.

Well... the P0507 came up again. The idle turned on me again.

If I go through the Idle relearn, the car idles fine. After driving around, it starts to idle at 1,500 etc..

The exhaust leak got worse, so I'm going to take care of this today

Probably tune issue, if i remember correctly, i'm on uprev and my nissan mechanic couldn't relearn idle because tune had it locked out.

You may be right. I'll have to get in touch with Kaizens next week after my track event at Thompson.

Got the exhaust leak fixed. No Cel light after 50 miles, but the idle is still screwed up.

I always see the p0507 code related to cleaning the throttle bodies. When I had everything off when installing the S.C., I did clean the throttle bodies. Not sure if this is related

Reset the ECU, went through the peddle release, tb closed position, and volume relearn. I used NDISIII to start the relearn. Waited for idle to get to 650 +/- 50 and then shut the car off.

Started it back up... idle like a kitten. Great.

Went to drive around the block... idle surge again.

Was curious about the purge valve connections and double checked the Stillen directions for it. Left side of the valve goes to back of the manifold. Other side goes to the EVAP. So everything looks good.

arrrrrgggggghhhhhh... back to the drawing board.

I am using 370z spark plugs (1+ colder, since I have a vq35HR). I've heard everyone using them once they go forced induction. Is there a reason I may have an issue? I left the standard gap on them.

My old man and I installed a magnusson supercharger on his C7 vette and we initially used 1+ colder plugs. Turns out they were no bueno and we tossed the stock ones back in.

Previously, i had the p0300 missfire, but I figured that was because the BPV was not opening up properly when going into vaccum... since I was using a high spring rated BOV (HKS SSQ) with the recirculation adapter.

tuner needs to set the idle

^ that. Either that, or give it some time for it to learn the fuel trims for the different IATs. I usually have a somewhat erratic idle when I first reset my computer or retune. But it usually settles down after a few days. I think it goes by number of ignition cycles before it stops the learning mode. It's probably something to do with the readiness monitors, but that's just a guess.

Went to Thompson speedway yesterday for a HSDE. I have to admit that I had 0 optimism going into the event. I brought basically my entire workshop with me.. extra belts, pulley, fuel pump, etc... Car handled very well and the charger just took me by surprise. Zero issues (minus the already known idle and cylinder misfire CELs). Power was great, which just gives the nismo an entirely different purpose on the track.

Update on the idle Info:
1) Decided to replace the throttle bodies. I got a set from a 370z with only 30K miles for $115.00. Cheap enough to replace. They will be here Thursday, so I'll install them on the weekend and go through the idle relearn procedure and post.

2) Found out that the P0300 Multi-cylinder misfire only occurs at startup on cold mornings. I'll replace the TB's first and revisit this.

3) Gas tank level reporting is off. Car gas meter showed that I had a quarter tank of gas and I had issues starting the car. I was very careful taking the fuel assembly out of the tank and installing it back.

EDIT:

On item 2 above, it may also be the TB. That p0507 is barking at me all the time due to ISC. If the T.B. is screwed up, at startup... it would most likely misfire.

check the maf harness extension as well as TB extension
most people who run the kit extend the harness itself instead of using the extension harness that comes with it which proved to be problematic.

I actually have their new revised harnesses.

I'm trying to fab up a new shield for the filter. It has been idling fine, but when the fans kick on... that is where the idle surge occurs.

This is most likely it.