Low RPM idle / Engine woes

[Olly350z]

Evening everyone, or perhaps morning?

 

So my Z has been sat for a number of months now but it finally came back on the road last friday. Ive noticed since then it has developed a low slightly rough idle. When fully warm it idles at 500rpm, with a slight cough and pop. Can feel the engine shaking slightly almost like it wants to cut out

 

I should mention that it had its plugs changed 10K ago and the oil / filter changed around 2K ago. Any ideas on whats causing this? The car has always been run on Vpower and rarely driven hard, it has thrown a CEL every now and then but these have always been O2 codes due to the high flow cats. When you put the aircon on it idles fine at 900rpm like it should

 

Also, I'm planning on another oil change soon, and would like to put a slightly thicker oil in for some piece of mind and added protection with rising temperatures. It does burn a little oil but not even near what nissan state. Can I have some recommendations for oil please

 

All constructive advice welcome

Edited May 7, 2017 by Olly350z

[Ekona]

Sounds like a dodgy MAF to me. Give it a clean with some carb cleaner first, see if that makes a difference, else try and swap with a known good one just to rule it out.

 

Thicker oil is not always a good thing on modern engines as they're designed for thinner stuff because of tight tolerances. What are you running now? Personally I'd go with a 5w-30 from Fuchs GT1 or Millers Nanodrive, better a quality oil than a thicker one IMHO.

[davey_83]

Whatever you do get oil with the right viscosity index, not just the right grade ie 5w30. I put the below in a few months ago and on first drive the car felt noticeably slower and warm idle pressure was up about 8-10psi. Fortnight later and it was swapped out for Motul 8100 5W-30 and the car feels back to normal.

 

[Ekona]

Another good reason to buy quality.

 

Exception is for emergency top ups, then anything will do as it's better than running on air!

[Tricky-Ricky]

Ran Shell Helix semi synthetic in all my cars, turbo an non turbo, great oil, had it analyzed once came back with flying colours, i ran the 10w40 in my VQ, never noticed anything like that with mine, the difference between a 10w30 and 10w40 is not great, so if the op is looking for a slightly thicker oil 10w40 would be fine.

 

Trouble is VI is not normally mentioned on oil cans, other than being lumped in with API GF CK FA etc classifications, and i have not seen anything lower than 80 mentioned, and most is 110, most modern oils are designed to be long lasting with higher mileages between changes, so the VI is very stable and doesn't normally degrade much in normal use/temps

 

If used hard on track i would use a fully synthetic due to the higher heat tolerance, and monitor oil temps before deciding on a diferent grade.

[Richf]

Have you put fresh petrol in it ? Fuel does go off over time

[Olly350z]

Yeah Rich had half a tank of vpower that friday night!

 

Last oil change i believe it had Fusch titan pro, was definitely fully synthetic and bought from Opie Oils. I just believe its had a slightly thicker oil in it in the past. From dropping out what it came with ive lost maybe 10-15psi across the guage. I have to be honest I never knew about more indepth knowledge of the oil side, always thought 10w40 5w30 etc was the same.

 

So what can I replace it with thats marginally thicker? Just marginally as I dont want to deviate too much from Nissans specifications

[Ekona]

Why do you want thicker oil? You'll lose performance as more energy will be used pushing the oil around rather than being delivered to the drivetrain.

 

I mean, I'd do it for FI applications as they will generate more heat anyway, but for NA? Unless it's a track monster, I'm not sure it's needed.

[Olly350z]

Dan Im only theorising at the moment due to some of the issues, or concerns shall we say im having. Personally I feel that the 5w30 is very thin, its almost got the consistency of water. And I wonder if it is giving that protection once the engine is fully warmed up, on a long drive where it does get driven harder then pootling around town.

 

What you must understand is that while Ive built my B18c after it died from oil pump failure, its taught me one thing, oil pressure is critical. Now moving onto VQ its an entirely different beast which I find daunting at times, no scratch that most of the time. Now from when I purchased the car and did an oil change I noticed a 10-15psi drop. As an example when cruising in 6th at 70mph / 2500rpm im only getting Id say 50psi indicated by the guage. On a hot idle after a drive id say its about 20psi. Different from when I purchased the car, so I can only assume it had a slightly thicker oil

 

Now having been to Abbey, Mark said it was fine and one of the healthiest sounding he'd heard especially considering its an 04. Its now developed this lower RPM idle which in my head ive put down to a number of possible issues

 

Plugs

Coilpacks

Maf sensor

Vacuum leak

 

Its obviously not been happy sat as its the third day and now the third dash light, now the wheel slip indicator. Noticed its coming on when light braking, as the Master Cylinder is making a sucking noise. All im after is brainstorming chap, Im not just going to go out and stick treacle in it haha

[Ekona]

A pressure drop is not a bad thing, it puts less stress on the pump for one as well as freeing up power as you're not creating the friction.

 

You have to remember that modern engine are built to vastly different designs, and are designed (and built) with much thinner oils in mind specifically. Back in the old days you might run a 20w80 in your old Bentley or whatever which would be pure mineral oil, but you'd never dream of using that these days! When you make an engine with fine tolerances you reduce the space between parts, and by reducing that space it means you need a thinner oil to run between it. Running a thicker oil means it never thins up enough to enter those passageways, and you end up with surfaces not getting any lubrication at all. Obviously, that's not what we want to achieve.

 

To give you a real-world example, some Porsche engines use oil to change cam profiles within the engine at various rpms depending on load, and if you try and run a thicker oil what happens is that the oil cannot travel down where it needs to operate the lobes etc, so you end up with an engine that simply doesn't work.

 

 

Given the VQ is designed for 5w30, I see no reason to move from that spec unless you're running the engine miles out of intended purpose (i.e. couple of big turbos, or smashing it off the limiter all the time on track). I'm not saying you'll do any real harm by running a 10w40 over a 5w30, but I'm saying the reasoning behind it is purely a mental one that will provide minimal benefits and will lose you power as the pump has to work harder. I might run a quality 10w40 over a cheap 5w30 (so a Motul over a Magnatec), but that's about it. Given that Abbey have given you a clean bill of health, I really wouldn't worry about it and I'm 100% sure it's got nothing to do with your current woes

 

 

Get the MAF cleaned up first, that's the most likely issue here.

[Rob350]

I too have the slightly low idle, whats the best way to clean the MAF once iv taken it out the intake??? Just squirt the hell out of it with brake cleaner??, or spray in a specific place?? Or avoid spraying somewhere??

 

Sorry to thread jump mate

[Tricky-Ricky]

Dan's right, however if the pressure drop only occurred when you changed the oil that's OK, but if its happens over the course of a day or two it can indicate bearing wear, but as Mark has given it a clean bill of health its unlikely, but something to bear in mind.

 

Changing from say a 10w30 to a 10w40 should not make a big difference in oil pressure maybe 5-10 psi at 4,000rpm, idle oil pressure is not an ideal indicator, 3-4,000rpm is where Nissan's pressure guide is taken, so it always better to check at the same rpm.

[Tricky-Ricky]

I too have the slightly low idle, whats the best way to clean the MAF once iv taken it out the intake??? Just squirt the hell out of it with brake cleaner??, or spray in a specific place?? Or avoid spraying somewhere??

 

Sorry to thread jump mate

 

 

I have used meths on a very soft artists brush to clean MAF for years, just be careful and gentle.

[Olly350z]

That definitely a point to note, the drop has only occured SINCE changing the oil. Other then that its a consistent pressure whenever its used.

 

Must also say that while Mark said it was Ok it was a visual and sound inspection, along with a bit of revving haha. Its no way a reflection on him or Abbey as they didnt even charge me

 

Can I use brake cleaner on the MAF sensor? And any idea what this whoosing / sucking noise is everytime I brake?

[Ekona]

I always use carb cleaner on MAFs, never anything else. Electrical contact cleaner would also work, dunno about brake cleaner.

[davey_83]

With mine changing from that particular Shell 5w30 (AG spec designed for a 1.3 CDTi Vaxuhall combo and possibly not the best for a VQ35) the move to Motul 8100 5w30 reduced the warm pressure effectively freeing up some power and response. Choice of oil filter also can have an effect on oil pressure too.

 

If you have a vacuum leak post tb, your mpg would be shocking even on a run.

[Olly350z]

Well Ive pulled the MAF out today and given it a qood squirt with carburettor cleaner and its now sat on the window sill blotting off which Ill refit tomorrow. No obvious signs of contamination but then its so small I doubt the naked eye could pick it up

 

Noticed ive got a leaky rocker cover again so im wondering if the plugs are wet. Think my next modification may be a new cover, god help my wallet

[Olly350z]

Refitted the MAF sensor and as predicted all its done is made things worse. Im reaching the end of my tether with this car. Since bringing out of storage and the body shop I've had nothing but warning lights all week. It started with an ECU light, which was O2 sensors again because of HFCs. I do have spacers before anyone asks so switched them off for the time being. Following day I had the airbag warning light, again switched off. Ive had the traction light flicker on and off as well despite being in crawling traffic.The car then developed a low idle, sitting in traffic you could hear it popping and banging with an idle of 500rpm. Switching the aircon on helped bring this back up to 900rpm. Pulled the MAF sensor out and gave it a squirt with carburettor cleaner as recommended on the forum. Plugged it in today and this is whaI'mim greeted with.

 

 

ECU light

ESP light

TRACTION light

And a fluctuating idle. At a complete loss as to how all this has come since its A.) Sat in my garage and B.) fitted spacers. Bar the idle it was ok yesterday for a short period

 

Edited May 7, 2017 by Olly350z

[davey_83]

Pull the plugs and replace if needed. Reset the ecu (warm engine), clear the lot and start from scratch - throttle body, pedal sensor, idle control valve resets all in order.

[chippychip123]

You need to read the codes really, but a low idle and occasional pop is quite normal if the air con is off!

One of the reasons a lot of people run it all year round, along with the misting up in winter

 

I personally have only ever used electrical cleaner on MAFs and I avoid touching the wires with anything as they are very sensitive

[Olly350z]

Its never dropped that low before with a shake to it thats the issue for cleaning the MAF. I only used carburettor cleaner as advised on the forums and no metal wires were touched :l

 

Will get the code reader in the week and see what it says

[Olly350z]

So I think I hadnt plugged the MAF back in properly from looking through the pictures I took before hand. So this morning I took it apart again, tripple checked everything then did the pedal dance to clear codes. Started it up and now no lights at all... So does that mean ive cleared them and its not detecting an error?

 

If thats the case then its good but Im still left with this lower RPM idle, going to attempt idle reset tomorrow. What else could cause a low idle?

[Ekona]

Failing MAF

[Tricky-Ricky]

It may be worth removing the throttle body and cleaning, the idle is controlled through the throttle stepper motor, and as the VQ generates a lot of oil mist due to its low load/idle PCV system, it tends to gum up the back of the TB which can cause problems, not saying its that for definite but worth a try.

[Olly350z]

It may be worth removing the throttle body and cleaning, the idle is controlled through the throttle stepper motor, and as the VQ generates a lot of oil mist due to its low load/idle PCV system, it tends to gum up the back of the TB which can cause problems, not saying its that for definite but worth a try.

 

Given my current track record with this car and how its bitten me every time with engine lights when Ive attempted something, how much of a DIY job would you say this is along with cleaning the PVC? Have to be honest Im rather embarrassed by how this car has kicked my backside everytime compared to the old Hondas...