GTR with a lumpy idle, need help

[93_jdm_fd]

So I have been trying to figure out what would cause my idle to sound like it has bigger cams which it doesn't. I have to idle the idle to about 1200rpm just so it's not loosening every bolt on my car. When cold it idles around 1000rpm and is really rough, when warm it's better but still does it and the idle is steady at 1200rpm.

I recorded a few videos today on my normal ride to work, cold start, semi-warm and fully warmed at work.

This is first thing in the morning

http://www.youtube.com/watch?v=m0k9FngCT8s

This one is just getting to my coffee place wit the car semi-warm

http://www.youtube.com/watch?v=xRHR8EL5pPc

This is coming out with my coffee and you can hear how ruff it is

http://www.youtube.com/watch?v=OXLRikkAVRE

Here is just sitting in the car and holding the camera steady, you can see how much the car is shaking

http://www.youtube.com/watch?v=KzBpu6uqoqY

Any finally at work(about a 10 min drive on the highway). It's not as bad but still sounds like a v8 and most people think it sounds cool, I would to if I had cams and was suppose to idle like this but I don't and it's driving me nuts.

http://www.youtube.com/watch?v=CQKdT7ccFXs

I have replaced both o2 sensors
spark plugs gapped from 0.6mm to 1.1mm and not difference at any gap
replaced all coils
replaced all injectors
tps is set to 0.45v
maps are cleaned and re-soldered
intake system was pressurized to 10psi and one vacuum line was fixed
checked for codes, code 55(normal)
CAS is set to the middle of its range(still looking for a timing light)If the cas is like a honda distributor you just set it to the middle and you should be good.


I need some more suggestions on what else to do? I have another ecu coming so I will try that when it gets here. It's only really bad when cold and when warm I can live with that cause it does sound pretty cool. It drives great and have no issues what so ever while driving, just the cold start idle is horrible and when warm it sounds like a v8 with a cam.

[Billy_Jack]

Compression then leakdown would be my next move

[93_jdm_fd]

Compression is at 160psi and our leakdown tester is garbage and leaks!!

[Skym]

Stock GTR cams can lump if you change cam timing with adjustable camgears. CAS, ignition map need to adjusted to suit. But from what I understand, it takes longer for engine to really move car when setup like that (shifted the powerband to mid, topend).

Another cause which happens on GTS as well is intake manifold gasket's have blown, but rpm can go up and down due to o2 sensors if leak is bad enough.

CAS is another that can cause missing when warming up, especially when bearings are on the way out which can pull timing by 1-2 degrees or so. But engine will get harder to start when cold, hot and gets worse over time.

I think it sounds similar to intake manifold gasket leak that I heard on a RB25DET. But it could be airleak near AFM's (engine starts stuttering) or coilpack failure that are similar. There are metal aftermarket intake manifold gaskets for RB26 to fix this intake manifold leak problem. But set CAS properly first via timing light, as sometimes it can be as simple as that.

Some use the procedure as shown in this PDF on page 10 -

http://www.linkecu.com/support/documentation/g1-engine-management-documentation/gtslinkinstructionmanual

It bypasses the black wire on coilpack loom near ignition module, which ECU sends signal to coilpack via ignition module. The idle stabilisation on ECU can make ignition timing go up and down by + or - 5 degrees or so and sends that signal through that black wire.

[93_jdm_fd]

I will pull the intake manifold off today and make sure the gaskets are good. I replaced all of them not long ago but you never know. I also want to have another look at every under the manifold while it's off just to make sure everything is good. I might also have a rear knock sensor unplugged? I removed it to put it at a better angle and can't remember if I plugged it back in or not. With the manifold on you can even get near the rear one.

I did remove the CAS the other day and spun the shaft, the bearing does sound rough. Like a skateboard wheel with dry bearing? Also when setting the timing do I have the unplug the TPS and set the CAS to 20(4 marks from the left)?

[MattiasJacobs]

21 or 22 degree I think. How does your car boost? Have you swapped out a different ignitor, or mafs. Sometimes they are just done resoldering won't help lol.

[93_jdm_fd]

My car boost perfect, 3rd gear floor it, 11psi, pulls really hard, shift to 4th, floor it, right back to 11psi and probably doing about 160km/h, lol. Yeah it boost awesome. I didn't try another ignitor or mafs yet. i don't have access to parts that I can swap. I did buy new coils, plugs and injectors with no change at all.

[Skym]

Sometimes the flanges are not straight.

From what I understand, from what others have said, ECU rev limit's engine, etc if knock sensor is unplugged or faulty (haven't tried unplugging knock sensor, so can't confirm).

When I had faulty CAS (been through 2 of them so far and the bearings on faulty CAS did feel a bit sluggish when turning CAS shaft), the engine got harder to start and engine felt down in power at lower rpm, etc. Also during warmup the idle was rougher. With replacement CAS the engine is smooth during warmup, revs fly to 1500rpm when starting engine (when engine has warmed up), not to just above 1000rpm like it did before.

Keep TPS plugged in (I thought CAS could be set easier by unplugging TPS to stop ECU using idle stabilisation on ECU, which from what I understand is triggered by idle contact inside TPS, but don't think you can do it that way). The ignition timing info (idle rpm, ignition timing) should be on a white sticker that's located on the underside of the hood on passenger side (near front of car). Timing light should display the number of degrees. The marks on crank pully are around 5 degrees apart from I think is left / drivers side.

[93_jdm_fd]

I removed the intake and found the rear knock sensor plugged. I guess if you have a bad knock sensor the timing gets retarded and I would probably feel a difference in the way it drives. It drives great, pulls hard. I also didn't see and split hoses or possible vacuum leaks either. Yesterday at work, just for fun I hooked up a vacuum tester to the factory boost gauge vacuum line and got 16-17 mm hg but the needle itself was bouncing all over the place. I though great something wrong internally. I tested the vacuum before at home with my really nice snap-on gauge and it was 17mm hg with a nice steady needle. I did this again today and 17mm hg was the reading with the needle steady, so that's good. What is the proper vacuum reading suppose to be at idle anyway? 17 sounds decent.

I have to get my hands on a timing light but for now I have a ecu coming and trying to track down a known good CAS.

[93_jdm_fd]

What about a weak fuel pump? Maybe at idle it's not pumping enough fuel but when I step on the gas the pressure comes up and making it run smooth? I've also been reading about rough idles and alot of people have intercooling piping that splits or pops off? this would cause a rough idle but would it also not effect boost? My car boost great so would this mean I don't have to pull my bumper off to make 100% sure nothing has popped off.

[Skym]

Check voltage to fuelpump. Fuelpump should be changed every 100,000km and fuelfilter in engine bay every 20,000km. Also change the sock filter on fuelpump when change fuelfilter in engine bay (if fueltank is run low all the time). I usually don't let it go below 1/4 tank, as no fuel = failed fuelpump.

When step on throttle, ECU injects more fuel and changes ignition timing to suit. Sometimes it's as simple as engine running too lean and when press throttle engine runs richer.

Intake airleaks can cause rough idle, especially airleak near AFM's (stutter). I run stronger bolt style intake hose clamps on intake piping instead of factory worm drive intake hose clamps.

[93_jdm_fd]

The car sat for almost 2 years in a heated storage garage with no engine. I installed the engine and replaced the fuel filter with a bigger one from a z32 before I put the engine in. I also never run any of my vehicles below 1/4, it just starts to suck up all the garbage in the bottom of the tank then.

Anyway it does make sense that the fuel pump can be getting weak, it has run like this ever since I put the engine in. I just found my cd disc with the complete service manual for this car so I will look into checking voltage at the pump. I will probably just get a new one and new sock anyway because my nismo speedo says 154,000kms which could be way off but still should be replaced anyway from the car sitting for awhile with no hardly any gas. I first started the car with gas that was left in it while adding $15 of new fuel.

[93_jdm_fd]

Anyone have an idle as to why my car idles around 1000rpm cold and once warm it idles higher which it should because the AAC adjust screw is set to idle at 1200rpm? Shouldn't it idle higher then when cold and come down to 1200rpm, not idle lower and then come up?

[BenC]

I would put some brand new plugs in it (or really scrub your old ones), Idle it for a minute and pull the plugs. See what they look like, see if you can narrow it down to specific cylinder(s) giving you issues

[93_jdm_fd]

I have 3 brand new sets of plugs I keep swapping in. I have ngk br7es or something like that. I have a set gapped to 0.6mm, 0.8mm and another set gapped 1.1mm. I drive for a few days, removed them and every plug has a nice tan color and every cylinder. I'm at the point now where it runs and drives great just has a rough idle and leave it. Right now I need another good running car beside me to swap CAS, coil harness, ignitor, AAC, mafs, tps, what ever sensor that could cause a rough idle one at a time.

I have been driving the car everyday since I put the engine in and it needs a clutch, upper control arms, the front pipe now has a small crack in it, the hicas light comes on once in a while so things things all need to be fixed to.