Quick Maf sensor testing question

[93_jdm_fd]

I've had this real annoying rough idle/misfire forever now and do my usual hours of searching this site and others for possible causes but nothing has solved my problem. I just read today that if I unplug both maf's with the key off, start the car and it runs than I have a maf sensor problem. Is this true because I did this and it runs and idles but won't rev past 3000rpm which you would expect with them unplugged.

I have cleaned both mafs before, replaced plugs, replaced coils, set tps, swapped out fuel injectors, checked codes, etc. It builds all kinds of boost and does not hesitate, stumble, stall anything while I'm driving, just at idle it's rough like a v8 with a giant cam or something, it even sounds like it at idle, lumpy like.

Here are a few videos of my problem.

http://www.youtube.com/watch?NR=1&v=CJLq1z3fZ3U&feature=endscreen

http://www.youtube.com/watch?feature=endscreen&v=dpBfs5-fSKI&NR=1

[gezed]

i ran the car with mafs unplugged and it runs fine just the 3k rev limit, get a multimeter voltage should be the white wire i think and idle voltage should be .8-1v and goes up to 5v or something when u rev it up

[93_jdm_fd]

Yeah I may have a slightly dirty element but they are probably fine. I will be checking every sensor out with my meter as per FSM to find out whats going on.

[Skym]

I think o2 sensors. If you disconnect o2 sensors it should stop. But they are usually compensating for a intake airleak which seems to make engine stay too lean which causes the missfire (lean missfire). ECU retune is the only way to solve it, if want to keep o2 sensors plugged in.

Sometimes rough idle can be engine fighting against thicker oil. I found this out when switching from 10w60 to 10w40 (to suit oiltemps, factory oilpressure). Factory is 7.5w30 for factory clearances, oil temps.

Sometimes it can be that the o2 sensors are stuffed (lazy, slow to react) and when combined with idle stabilisation on ECU, it makes rpm go up and down. If o2 sensors have done over 40-60,000km, replace them.

Other causes of missing are injector and coilpack looms that have gone hard due to heat.

[Ramius83]

What RPMs are you idling at? What is your vacuum reading at idle?

[Ramius83]

Also, are you able to data monitor anything with a scan tool or Consult? I am wondering what your A/F alphas are while it is idling like crap. If they were reading 125+% lean or 80-% rich, then I would suspect O2 sensors, air/vacuum leak, etc? If both are reading the same, could be related to same item(s)......

[93_jdm_fd]

It idles at 900rpm and the rpm is steady it just the engine is shaking not the needle on the tach. The vacuum reading on the factory guage is steady around -4(just under the line between 0 and -7). I hooked up a another vacuum guage to the intake manifold and got a steady needle reading of 17, I forgot what the guage uses to measure the reading though. I can remember though that it was at 17 and the needle was steady and not boucing around with the engine shake.

[93_jdm_fd]

Now on the drive home today from work it was almost the rpm was set at steps like giving it gas it almost feels like it looses power and then goes again then higher up the rpm it hits a wall again and then goes. I ordered two new o2 sensors today but they won't be here until friday. I got two from a 94 v6 3.0l maxima which uses the NTK/NGK ones that seem to be most common to use.

[93_jdm_fd]

I replaced both o2 sensors on my lunch break today, disconnected the battery to reset to ecu. Starting it up after work and it seems to run better when cold but still has the slight shake/miss at idle. I bought the car without an engine, found a blown one, rebuilt it and this is how it ran ever since I first started the engine for the first time last summer.

I got the block bored out to 86.5, wiseco pistons, crank ground and collar added, acl race bearings(rod and main) tomei oil restrictor, and an oem nissan complete gasket kit. I had the engine block bored at one shop, the crank done at another shop and I put the engine back together myself. I am a licence mechanic and have done many times before. Anyway could this v8 with a cam idle be becuase the enigne was not properly balanced? Since the pistons are forged, crank has been ground and a collar added?

I just don't know what else to do. I can't just go start replacing stuff for fun because it's starting to get expensive for nothing. Coils, injectors, o2 sensors, what next, CAS, TPS, MAF's??

[Frankyy]

unplug your injectors 1 at a time if the idle changes for everyone of em you just eliminated a big problem

unplug 1 maf at a time if the car dies or idle changed then it's a maf

pressure test your vac system for any possible leak, it's alot easier to hear leaks while the motor is off then when it's running( I found 6 yesterday i didn't even think I had any).

just throwing ideas out there hope something helps

[93_jdm_fd]

How would I go about pressure testing my vacuum system, I understand the concept of doing this but where is the best place to hook up a vacuum guage? I replaced alot of my vacuum lines when I had the engine out and on the stand but I ran out of vacuum line. The 3 or so that I didn't replace could be whats causing my problem.

[danwit]

I would also test your coilpacks while your in there. Unplug each one at idle, if you unplug one with no difference its no good.

To pressurize your intake, i went to home hardware and made this:

Put it on any pipe thats pressurized, hit it with a compressor and listen for leaks.

[93_jdm_fd]

I was looking at pressure testers last night on a google search. Looks pretty straight foward. I tested the old coils and they were fine but for fun a bought another 6 and still made no difference. I replaced all 6 injectors already with a know good set, new bottom seals and top and o-rings and still made no difference. After replacing the o2 sensors on friday, reseting the ecu I did notice difference in the cold start up and it seems to run better but still at idle it has the pop/shake like the hundreds of threads started on other sites of a rb series engine idle rough.

[93_jdm_fd]

One thing I didn't do was gap the spark plugs. I just put in NGK bkr7e plugs and just assumed they came pre-gapped. I did check a few of them with my spark plug gap tool but it only goes as low as 1.12mm, I couldn't fit that in either of the plugs so I just assumed they were at 0.8mm. I've even read of people gapping them to 0.65mm.

[Frankyy]

I gOt a 3 inch end cap for PVC plumbing grinded the threads off and undid the Ic piping right after the twin turbo cast peice and clamped it down with the existing coupler drilled in a valve in the end cap of course