Misfire? Hesitation? Dead Spot?

[Bee-RSkyline]

Having trouble diagnosing what is likely an ignition problem but who knows?

Slightly inconsistent idle, drops very slightly now and then and can get worse to the point of hunting when engine is really warm.
Will not hold a constant speed @ 50-60kms bucks on and off on light throttle pressure.
Seems there is a dead spot around 2000rpm. revs will drop if held, but will push past.

TPS sensor reads .48V on idle and increases steadily to just over 4V @ WOT.
MAF has just been removed and cleaned.
Nistune ECU

Any ideas?

[gtrjerry73]

Sounds like your Maf. The contacts inside the plastic box with age and heat become separated and cause all these issues would be worth trying seeing as its easy and free unless you take it to an electronic repair shop (I would reccomend it cause if your not good at soldering then it will just come apart again) that's my best guess though especially if it gets worse as the underwood temps rise.

[Skym]

Slightly inconsistent idle, drops very slightly now and then and can get worse to the point of hunting when engine is really warm.

o2 sensor is probably picking up a intake airleak and adjusting A/F ratio lean, rich. When combined with idle stabilisation tables, ECU is adjusting idle up and down. If unplug o2 sensor engine should have a smooth idle. Sometimes using too thick oil can cause idle instability problems. I found that out when switching from 10w60 to the correct oil for my cars engine which was 10w40. Factory is 7.5w30. After oil change, idle was very smooth. Also engine felt less responsive at lower rpm with thicker oil (10w60), but the oil change (10w40) fixed that.

Will not hold a constant speed @ 50-60kms bucks on and off on light throttle pressure.

Check for a intake airleak behind MAF, either intake hose clamps are not tight enough, hole in rubber intake pipe behind MAF under intake hoseclamp, cracks between ribs on rubber intake pipe behind MAF, etc. When there's a airleak there (just behind MAF) engine starts stuttering.

Also if hits idle contact inside TPS, ECU switches to tables which makes the car buck. That is normal, but how much it bucks can be tune related.

Seems there is a dead spot around 2000rpm. revs will drop if held, but will push past.

Sounds like TPS settings (engine suddenly goes lean = hesitation before accelerating), but could be due to airleak behind MAF making ECU select wrong load cell on fuel, ignition maps which could produce similar symptoms or using incorrect oil.

MAF has just been removed and cleaned.

Could be airleak behind MAF, check intake hose clamp.

It's a process of elimination, but also can fix other problems you didn't know about and get a smoother running engine.

[Bee-RSkyline]

o2 sensor is probably picking up a intake airleak and adjusting A/F ratio lean, rich. When combined with idle stabilisation tables, ECU is adjusting idle up and down. If unplug o2 sensor engine should have a smooth idle. Sometimes using too thick oil can cause idle instability problems. I found that out when switching from 10w60 to the correct oil for my cars engine which was 10w40. Factory is 7.5w30. After oil change, idle was very smooth. Also engine felt less responsive at lower rpm with thicker oil (10w60), but the oil change (10w40) fixed that.

Can I run the car without the stock O2 sensor until my AEM Uego arrives? (Base tune on the Nistune board was done with a wideband o2 sensor and then replaced with stock sensor)
I'm running Motul 300V, can't remember the weight (theives stole the remainder of the can)

[Skym]

Can unplug o2 sensor if ECU tune is safe (look at A/F ratio plot on dyno chart that was done with stock narrowband o2 sensor unplugged) and don't have a failing fuelpump, etc. Usually most check with a wideband after unplugging stock narrowband o2 sensor to check A/F ratio, so might be wise to wait until you get the wideband.

Could be the Motul 300V 15w50 which is too thick for road use. The w50 is used when oiltemps are high (over 100 degrees C) on racetrack. Probably wouldn't reach over 100 degrees C on the road with lightly modded engine (maybe when on a long motorway trip), so the w40 is usually enough. But to select oil weight properly you need aftermarket oiltemp, oilpressure (match to factory figures) gauges.

[Bee-RSkyline]

thanks skym. unplugging the o2 sensor didn't affect idle at all.

leaning towards an intake leak or sensor failure now.
don't think it is right behind the MAF as it there is only about 12" of piping before the turbo & it seems really solid.
gonna take a while to go over all this piping.

[Skym]

If have Nistune tuning software, consult cable, laptop, you can check for sensor error codes, datalog sensors (good way to check stock narrowband o2 sensor, MAF voltage), etc and watch what ECU is looking at on tables, maps, etc in realtime. Sometimes the coolant sensor fails, but that should be obvious through Nistune tuning software.

[Bee-RSkyline]

Vids. Any thoughts?
I'm leaning toward a MAF issue now, as the part # suggests J30/Z32 MAF however the pigtail is definitely not the same.