I have a '95 Q45 and I've been having problems with it running rough and stalling out. I haven't been able to 100% replicate what causes it but it usually happens after I stop at red light or stop sign. I also noticed that the rpms fluctuate when the car is idling. This only happens once the car reaches operating temperature. Sometimes on a cold start it will run terribly. It will almost stall out and the exhaust will spew thick white smoke. This is usually fixed by shutting the car off and starting it again. Does anyone know what is causing this and how I can fix it?

I had the same issue exactly with my '96 Q45.

Turns out it was the Ignition coils. Replace all with OEM and also replaced spark plugs and was Good To Go.
Make sure they are OEM, there is a difference.

Thy cost about $170.00 each

Sounds like a mass air flow meter (MAF) to me. Sometimes it's just loose pins in the connector that can be tightened with a pick. Try gently wiggling the connector at idle and see if the idle changes.

I've also had a cold solder joint in the MAF. Try gently tapping the black box on top of your MAF at idle, and see if the idle fluctuates. If so, and you're handy with a soldering iron I've been able to remove the cover and re-solder the three points where the connector attaches to the board. The cover is stuck in place with black silicone RTV around the edges that you can scrape away with a small screwdriver or pick. You can clean it up and reseal it with more RTV when you're done.

Other common issues could be a bad fuel pump control module (FPCM) that has overheated due to a failing fuel pump pulling too much current. If you hear a "hive of bees" noise behind your back seat when you're below 1/2 or 1/4 full, that's a sure sign you need a new fuel pump.

Coil failure is way down on the list of common issues the G50, but at this age anything is possible.

do you smell unburned fuel out the exhaust?

My Q had all the fuel pump issues settled last year as well as the MAF, so the ignition coils were checked and that was the new issue.

Replace the coils any how because down the road they will need changing, and OEM won't be available then probably.
Also OEM fuel pump and controllers might be scarce too

3Q Jay wrote: ↑

Sat Oct 30, 2021 11:14 am

do you smell unburned fuel out the exhaust?

Sorry for the late reply. I forgot I even posted this and just remembered today. Yes I do smell unburned fuel out of the exhaust but only when it is stalling.

Well, unburned fuel is a problem. The question is--why?
Suggest verifying measured fuel pressure at the rail next--verify at idle, then immediately after shutdown, then again 5 minutes after shutdown.
This is to make sure your injectors are not leaking fuel into the cylinders, which is a recipe for a rapid death of your VH45DE.

Do not ask how I know. Leaky injectors will hydrolock the engine.

When we're your injectors last cleaned and flow bench tested?

Its either I have the same issue or a similar problem.. Because you pretty much described whats wrong with my 98 Y33 Q45 and I pretty sure one these answers on here is the Problem.. Thanks guys

WeeGee West 714 wrote: ↑

Fri Feb 25, 2022 2:08 pm

Its either I have the same issue or a similar problem.. Because you pretty much described whats wrong with my 98 Y33 Q45 and I pretty sure one these answers on here is the Problem.. Thanks guys

exactly whats happening with my 99, let my know if u figure anything out lol. heres a vid of my y33 troubles https://www.youtube.com/watch?v=1XE5rb3ENuw

Hmm…the idle fluctuation sounds like a vacuum leak. I had a bad “dancing idle issue for YEARS, never could figure it out. A shop suggested a vacuum leak, I found a cracked hose but the main one was the intake plenum gasket. If you’ve never changed it, that might be something to consider. You’ll usually find other things along the way.

I also had a hell of a time chasing down an issue on my 2 other vehicles: crazy high idles at random, and almost self-moving when driving (so high I would have to shift into neutral and turn off engine at 2,500 rpm). Turns out the throttle bodies were getting gummed up from too much short distance driving. Somehow getting like “stuck” a bit.

Ignition coils usually give off a blinking check engine light (but so will a bad intake gasket leak). You’ll usually get a code specific to that cylinder coil (also had that issue for months on my Maxima, in 1 cylinder only, even with new coil. Turns out, it needed a Hitachi or Nissan coil, it didn’t like the others).

98_Q45 wrote: ↑

Sat Mar 12, 2022 2:33 am

Hmm…the idle fluctuation sounds like a vacuum leak. I had a bad “dancing idle issue for YEARS, never could figure it out. A shop suggested a vacuum leak, I found a cracked hose but the main one was the intake plenum gasket. If you’ve never changed it, that might be something to consider. You’ll usually find other things along the way.

I also had a hell of a time chasing down an issue on my 2 other vehicles: crazy high idles at random, and almost self-moving when driving (so high I would have to shift into neutral and turn off engine at 2,500 rpm). Turns out the throttle bodies were getting gummed up from too much short distance driving. Somehow getting like “stuck” a bit.

Ignition coils usually give off a blinking check engine light (but so will a bad intake gasket leak). You’ll usually get a code specific to that cylinder coil (also had that issue for months on my Maxima, in 1 cylinder only, even with new coil. Turns out, it needed a Hitachi or Nissan coil, it didn’t like the others).

alright damn sounds like its what i thought and im gonna have to dig into the plenum and intake runners, thanks for the insight. The maf and throttle body were the first things i checked and cleaned but no fix there. Atleast it might not be a coil then since theres no blinking light. i'll scan it again today because the check engine light came back on 260 miles after i cleared the code. Damn nissans lol

checked the code at 120626 miles after driving with the CEL, now its a P0420 catalyst system efficiency below threshold bank 1. I'm getting so damn confused, everytime the light comes back, its a different code. clearing the codes again and going to drive and do more research. trying to get money together so I can start to work on it myself. Saw something in a G50 thread about the ecu causing the egr to not function properly, and im thinking since the codes keep coming back different, there may be something wrong with the computers, would a replacement ecu or a tune potentially help? where would I go for something like that