Cleaning the IACV on a Stagea RB25 Neo

Seriously, it couldn’t have happened at a worse time. I’ve taken a week of work to move house twenty clicks down the road (and if you want to read about the torture involved and learning how to work with something French, you can check it out right here) and on my first day back at work the Stagea died an idle death at a busy roundabout right in the middle of school drop off time…

Two warning lights popped up first..

And as you do when they light up the dash, your heart sinks. “Not the coilpacks again, the second hand splitfires have been so good up until n-” and then it completely died. The needle dropped, the engine switched off. I fired it up again and it died straight away. Flicking the hazard lights on I tried again and it died then swore, tried it again and it died.
What a s#%^ place for this to happen.

The next time I started it up with one foot on the brake and one on the accelerator (it’s an auto) and kept the revs high which got it moving enough to crawl up a nearby hill before it ran out of puff and I had to park it and pop the bonnet.

Now at this point I started running though my head what it could be – the last time a similar thing happened was with my Rx7 and that turned out to be a vacuum hose that had dropped off my air intake. Not the case here.
Maybe the MAF sensor had broken? I’d re soldered everything a while back, maybe it had fallen over this morning?

I kept trying to start it and hold the revs but ultimately just flattened my battery. A great start to my first day back.

I’m going to need some help here..

I text my boss to let him know I’d be late, I text my wife to ask for a jump start and before you know it there was her little Lancer trying to coax some life back into the Stag.

Mitsubishi Lancer jump start

Unfortunately even though it helped start it again, it would still die as soon as you removed the leads it would die again. With the kids in the back of her car and needing to get to school and me having to keep a foot on the pedal to keep the revs up – it was a too much of a challenge. Time for someone who has more of an idea of what it could be…or maybe a tow truck.


So I got onto the RACQ. $200 and something later (signed up to roadside assistance and because I needed it within 72 hours of sign up, there was a $100 call up fee) and 40 mins later a happy mechanic by the name of Steve rolled up and asked if I could stay on the pavement and out of harm in case anyone careened into my parked car (highly unlikely where it was parked but he’s just doing his job.)

After twenty minutes of having a look, firing it up a a couple of times and even checking the oil levels (no I know they’re good) he brought out the tools and tightened up the throttle cable to great success. It started, it idled, it didn’t switch itself off again.

Seriously, just a stretched throttle cable? That’s all it was??

Stagea throttle cable
This thing stretched just enough to drop the revs..

He also test my battery and discovered that it had dropped a cell (of course had one that he could replace it with in the truck for the low price of just $160..) and $360 later I was back on the road…

So it’s working, why am I cleaning up the IACV then?

Because for the last twelve months or so it’s had a strange idle. Not a concerning idle to the point where I wondered if it was about to fall over but the occasional vibration at the lights (which I put down to worn out engine mounts) and recently, I’ve noticed a little bounce on the tacho. Taking off and cruising seems to be fine, it’s just when it idles at any length of time the small jumps start to appear:

A search around the net seems to point at people cleaning their IACV and smoothing rough and strange idles out…so let’s try that!

(QUICK EDIT: I discovered accidentally today that this strange idle and a clicking sound only seems to happen….with the air conditioning on. Wonderful. Even with the new battery humming away, the air con seems to be a bit of a load on the engine. Thankfully from what I’ve read cleaning up the IACV seems to fix this too! So now there’s extra incentive to get this thing off and clean!)

(ANOTHER QUICK EDIT! 8 months later and I was trying to work out why my consult port wasn’t doing anything. I was trying to do a scan with that one weird paperclip trick but to no avail. No flashing engine light, nothing. Eventually I worked out that it was a fuse that it goes through that had one – an 10amp engine control fuse – this one:

Stagea obd 1 fuse

Putting in a new fuse caused my revs to jump up another 500 rpm (and this was after I’d tuned everything like you’ll read below), suggesting it may have been broken for quite some time and possibly part of the problem. So before you get cleaning, maybe try this fuse first?)


Anyway, onwards with the tutorial!


Nissan Stagea IACV location
Here’s what’s coming off. Drivers side at the back of the block.
These three hoses contain coolant so we’ll be making sure the engine is cool before removing them

What you’ll need: 

A 10mm spanner. Once again my 10mm ratcheting spanner that I bought way back to get the rocker cover off a GC8 WRX comes to the rescue. Remind me to buy more ratcheting sizes as this one is brilliant. Also a 10mm socket wrench for the bottom two bolts (the ratcheting one doesn’t work down there sadly, not enough room.)

Pliers to get the hose clamps off. I like locking pliers for this purpose.

Carby/ throttle body cleaner. I was going to try degreaser but since YouTube and the world wide web in general seem to swear by the stuff, who am I to argue?

A stubby screwdriver to adjust the idle screw


Another gasket (part number is Nissan 23785-AA000). Apparently if you take it off carefully, you should be able to use it again. I’m planning to go really carefully here. (Edit: It broke easily. {Permatex time!)

Gasket maker/seal. Just in case. I have some leftover Permatex Black from the WRX job. Provided it hasn’t hardened to the density of a rock, this could come in handy.

Screwdrivers to scrape the old broken gasket off…

A towel under the coolant hoses

Right then, lets get this thing cleaned!

Remove the three small hoses (you may get a dribble of coolant. I didn’t but had the towel there just in case.) A slow steady pull was all I needed for all three to slide off.

Disconnect the grey plug on the wires coming out of the IACV/AAC

Undo the four bolts, pull unit away slowly and try not to damage the gasket (mine just fell to bits no matter what I did)

Remove the larger hose connected at the bottom and now it’s free!

IACV Stagea

Now I thought it’d be absolutely caked with carbon but this is what I’d call a light smattering. Still it’s out of the car now so no point throwing it back in there without a clean first. I used plenty of carby cleaner with an old toothbrush and plenty of cotton wool buds to really get into the corners and crevices.

We started with this:

Dirty IACV Stagea

The tools got a workout:

And things looked a little brighter!

Clean IACV Stagea Neo

Now that it’s cleaned, we do the reverse order to pop it back. But first, a layer of the black goo:

Back we go!

Attach the big hose

Line up the unit and bolt it back in (top tip: Don’t tighten the bolts until all four can go in easily. There’s a bit of jiggling and swearing involved)

Reconnect the grey plug (I almost forgot this)

Reconnect the three coolant hoses.

Now bleed the coolant system

This bolt here next to the little sticker is to bleed the coolant of air. Remove bolt, start car, wait til a little coolant comes out, stop car, put bolt back in, well bled.

With everything back in, now we fine tune the idle.

There’s a few guides to do this but here’s what seemed to work for me. Disconnect the TPS plug (that’s this one in the middle of the engine towards the back)

Start the car. Mine started but dropped the revs without the TPS giving it a hand to cough up a couple of warning lights. That’s okay, we want it to warm up without any assistance.

Wait for the car to get to proper warm up temps (ie temp line on dash at halfway)

Adjust the IACV screw to get the idle revs to 800-900 rpm. Clockwise lowers the revs, counter clockwise brings them up. The adjustment screw is here on the IACV and you’ll need a stubby screwdriver to turn it either way.

idle adjust screw stagea

Reconnect TPS plug, adjusting again if need be. (I may have to adjust it again with the TPS in at the next cold start, we’ll see how we go)

Initial test

I took the wagon for a quick blurt down the road and so far so good. With the IACV clean and the idle back up to where it should be, things do seem a little smoother. The true test was the air conditioner – so I turned it on, the revs dropped slightly (as expected with the power draw on the engine) however…no needle bounce when at the lights! No flickering lights on the dash when it’s in use. The air was cold, the revs were behaving. Glorious!

Now onto the next job!


Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.