Low idle

[DoubleChevron]

Hi guys,

a '92 3.9 V8. When it's good an warm it idles way to low. about 400rpm I'd guess, which obviously makes it idle rough as buggery. Is there a way to adjust this? I'm pretty sure there is no "dud" components as everything works fine, cold idle is higher, it idles nicely with the A/C running.... It just needs the settings for hot idle increased by about 200rpm... infact A/C on revs would be perfect.

Any ideas :confused: It doesn't stall amazingly ... but idling so low can't be good for it ... the oil pressure must drop away to nothing at such low rpm.

seeya,
Shane L.

[PhilipA]

The stepper should always aim for about 650-700RPM and it sounds like its working if the idle with Ac on is higher.

I suggest you clean around the throttle blade and the oil vent outlet into the throttle area with carb cleaner. Also clean the stepper cone and its seat.

If that doesn't work next step is to set the Kerb idle at about 550RPM, To do this block off each end of the stepper bypass hose ie the stub on the throttle body and the stub on the stepper housing, and loosen the grub screw you will see on the top of the throttle body. This is a bypass.

It should fix it just by cleaning and make sure you clean the throttle blade itself as well as the throat in the vicinity.
Gee an easy one!
Regards Philip A

[DoubleChevron]

The stepper should always aim for about 650-700RPM and it sounds like its working if the idle with Ac on is higher.

I suggest you clean around the throttle blade and the oil vent outlet into the throttle area with carb cleaner. Also clean the stepper cone and its seat.

If that doesn't work next step is to set the Kerb idle at about 550RPM, To do this block off each end of the stepper bypass hose ie the stub on the throttle body and the stub on the stepper housing, and loosen the grub screw you will see on the top of the throttle body. This is a bypass.

It should fix it just by cleaning and make sure you clean the throttle blade itself as well as the throat in the vicinity.
Gee an easy one!
Regards Philip A

Thanks Philip,

I'll give it a crack tonight if I get some time.... I haven't broken the car for nearly two weeks, so I better do some more tinkering :angel: :wasntme:

seeya,
Shane L.

[DoubleChevron]

Ok, I whipped the housing off that contains the idle stepper motor so I could see what I was doing. Just like everything else under the bonnet of this car, it looks clean and like it's been apart in the near past and checked. Everything looks checked and replaced, wiring, hoses, radiator .... It one of the things that stands out when you lift the bonnet.

http://www.aulro.com/afvb/attachment.php?attachmentid=91111&stc=1&d=1424692332

I just gave it a quick wire brush with a soft stainless steel brush and sprayed down the guts of the drive with some silicon spray. Note: the washer broke up as soon as I unscrewed it. fortunatly my bag of leftover orings and gasket has a slightly thicker version in the exact size (it'll be fine the stepper motor should just drive the drive out a fraction further).

http://www.aulro.com/afvb/attachment.php?attachmentid=91112&stc=1&d=1424692332

http://www.aulro.com/afvb/attachment.php?attachmentid=91113&stc=1&d=1424692332

Note: the metal tag sitting out on the housing that has chopped up the last seal. I just ran a file over it to level it.

It does seem to idle much more nicely now. I guess we'll see next time it's good and hot if it's made any difference though.

[PhilipA]

OK , but the main reason for slow idle is that the throttle plate gets dirty and therefore reduces the amount of air that passes it when it is just cracked, so make sure you clean it also.
Regards Philip A

[DoubleChevron]

This is one thing that's annoyed me since the first time I lifted the bonnet:

http://www.aulro.com/afvb/attachment.php?attachmentid=91120&stc=1&d=1424692332

http://www.aulro.com/afvb/attachment.php?attachmentid=91119&stc=1&d=1424692332

This looks absolutely ****house.... It'll be the gas fitter that did this. You can clearly see the intake leaks at the air cleaner connector and where that breather hose attaches.

http://www.aulro.com/afvb/attachment.php?attachmentid=91118&stc=1&d=1424692332


http://www.aulro.com/afvb/attachment.php?attachmentid=91117&stc=1&d=1424692332


http://www.aulro.com/afvb/attachment.php?attachmentid=91116&stc=1&d=1424692332

How could the gas fitter allow this to leave his shop like this. Anyone that sees it is going to say "whatever you do don't use XXXXX for gas conversions".

I'll need to move the air cleaner and sensor 1/4" further forward so the rubber flexible bit fits in there with the gas mixer ring.... I'll need to somehow fix up that ****ty hole slashed in there for the breather too. (I'll get my uncle to checkout how the rest of the gas has been done just to be on the safe side when I next see him. He retired about 2years ago, but specialised in gas conversions for about 15years prior to that).

[DoubleChevron]

shouldn't there be a rubber seal between the sensor and air cleaner housing ?

[img]http://www.aulro.com/afvb/attachment.php?attachmentid=91121&stc=1&d=1424692332

http://www.aulro.com/afvb/attachment.php?attachmentid=91122&stc=1&d=1424692332

Wow ... Look how HUGE the intake restriction is from the gas :eek: :eek: :eek:

That would have to make a big difference to both gas and petrol performance :confused: The weird bit is it seem to run really nicely .... I would have thought that would kill performance.

Has any tried a BLOS carby to get rid of the huge inlet restriction ?

http://www.aussiefrogs.com/forum/redirect-to/'redirect=http%3A%2F%2Fwww.ebay.com.au%2Fitm%2FBLO S-Propane-Carburetor-LPG-Carb-Mixer-Better-Performance-and-Mileage-%2F320994547616

seeya,
Shane L.

[PhilipA]

So the low idle is on petrol or gas?

If on gas the stepper will have not have the same effect unless there is a feed in to the petrol ECU.

It will still raise idle for aircon as it opens a set step for aircon on, but probably won't control idle as it cannot change fuel/gas input only air and that depends on how well the gas is calibrated.

In the gas case you will have to open up the air bypass , then probably your aircon step will be too high.LOL
Ah the beauty of gas.
Regards Philip A
And look at the dirt in the intake! There should be an oring between the MAF and aircleaner. Boy what a crap job.

[DoubleChevron]

So the low idle is on petrol or gas?

If on gas the stepper will have not have the same effect unless there is a feed in to the petrol ECU.

It will still raise idle for aircon as it opens a set step for aircon on, but probably won't control idle as it cannot change fuel/gas input only air and that depends on how well the gas is calibrated.

In the gas case you will have to open up the air bypass , then probably your aircon step will be too high.LOL
Ah the beauty of gas.
Regards Philip A
And look at the dirt in the intake! There should be an oring between the MAF and aircleaner. Boy what a crap job.

Pretty sure it's both petrol and gas. I'll have to check. It's only done a few thousand kms since the gas was fitted (see how it's all shiny and brand new) ... Next job is to clean the throttle butterfly (I'm pretty sure I can see it shiny in the piccies above :) ) ... to be honest though, I can't believe this is all 280,000kms old. Everything is remarkably clean. Someone has fixed this up in the distant past (distant time past I'd say, but not a lot of miles ago).

seeya,
Shane L.
PS: I don't reckon that'll be dirt there.... look how HUGE the breather hose is ... surely that can't be right, shouldn't it have a metering orifice at the end of it ? ... it'll be crankcase fumes/oil residue

[PhilipA]

There should be a T piece near the plenum with a small hose to the plenum. The T. Piece should have a very small hole <1mm which leads to the plenum. This creates vacuum for the crank ventilation.
Regards Philip A

[bee utey]

If your breather hose from the drivers side rocker cover is connected to the inlet duct, remove it ASAP. It should remain connected to the port on the side of the throttle body at all times. The way the LR breather system works this is the best way. Fitters that hook a breather into the front of the mixer think that the LR breather is the same as Holdens and Fords with a PCV system, which it isn't. As Philip said, you need the tee piece with the small vent to the inlet manifold. The size of that breather sets your base idle speed as much as any other component. Go get a genuine one, they're not that dear (I paid $18 for the last one).

The problem with moving the breather is that the engines dirty fumes are being put into the throttle body in a way that they enter the IAC valve and goop it up. With the stock breather only on full throttle do fumes enter the throttle body and they are drawn through on the front side away from the IAC so don't enter it. At low throttle the fumes are drawn into the engine via the small branch of the tee. It's really quite clever and LPG fitters do love ruining it.

This is a home made brass tee, I had to reduce the small hose outlet with an internal jet of around 3mm to correct it.

http://www.aulro.com/afvb/attachment.php?attachmentid=48941&d=1341968784

Note the mixer, it's one of mine at 46mm ID, see below.

As to the mixer ID, the maximum size that a 3.9 can run successfully is around 46mm. Most of the off-the-shelf mixers are around 42-44mm and will reduce your top end power a bit, you may lose say 500 rpm off your power band. Down low you'll never notice it. I've re-profiled plenty of mixers in the lathe to increase their ID and make sure the gas outlet channel is as clear as possible.

Oh and do get some o-rings for the MAF, they're easily lost so keep a spare handy. I make mine by super gluing cut down larger ones out of a random collection I once got at a garage sale. You can probably buy bulk o-ring rubber at a bearing shop.

[DoubleChevron]

Thanks for that picture.... A simple picture speaks a thousands words sure is true :) I'm pleased we have some gas guru's on here ... 'cos I'm sure my uncle would have said "that's right the way it's done" too as he's not into "rovers" at all. He hates old cars, he'd have told me old Rovers are unreliable heaps of **** and get rid of it ( gotta love grumpy old mechanics, he'd say the same thing about my citroens too :D ).

OK, I'll chase up one of those brass fittings. I'll have to find a new non-butchered bit of flexible intake hose too.

The gas installer has done such a nice job in some places.... and such a ****house job in others. The gas gauge also doesn't work. I know the float is working as you can hear is squeaking as it moves around under 1/2tank. I imagine it's not wired in.... (or the sender in the tank is cactus). I'll have to try and find the wiring schematics for the gas system to figure it out. I'm not in a hurry to take it back to the guy the installed the gas.

The gas gauge doesn't really worry me ... just keep a quarter of a tank of petrol in there at all times and switch it over if it runs out.

Hey Bee utey, have you tried one of those BLOS gas carbies. I googled it and they seem to have a very positive following :)

seeya,
Shane L.

[bee utey]

Hey Bee utey, have you tried one of those BLOS gas carbies. I googled it and they seem to have a very positive following :)


Never been tempted, they look like a device like the equally well loved hiclone to me. Even the biggest available one seems a load smaller that a plain well profiled 46mm mixer. I think their heyday was in the eastern european dark ages before sequential vapour injection transformed small engine performance on lpg. IMHO don't mess with a simple easy to sort system unless you have a passion for complexity. Then go for SVI and electronic tuning instead.

Oh and I just checked my spare breather tee, the jet size is 1/8" or just over 3mm, not 1mm as first mentioned.

[PhilipA]

Specialists like Graeme Cooper used to sell a ready made brass "T' with the correct holes as the OEM ones are plastic and die over time or if disconnected too many times.
they probably still have them as there are a lot of D1V8s around
Regards Philip A

[DoubleChevron]

Specialists like Graeme Cooper used to sell a ready made brass "T' with the correct holes as the OEM ones are plastic and die over time or if disconnected too many times.
they probably still have them as there are a lot of D1V8s around
Regards Philip A

Thanks Guys,

I'll see if I can buy one pre-done. It'll be easier than soldering a brass "T" shut and drilling it out to 3mm. here's the plastic version on ebay by the looks of it:
http://www.ebay.com.au/itm/Crank-Case-Breather-T-Connector-Land-Rover-Discovery-Range-Rover-Classic-V8-EFI-/281100928620?pt=LH_DefaultDomain_15&fits=Model%3ARange+Rover&hash=item4172ebc66c

seeya,
Shane L.

[DoubleChevron]

Well I played with the brass screw on the gas mixer hose. 1/2turn has lifted the idle so it has a nice smooth, still quite low idle when hot on gas.

The side effect is a high idle when cold. With a manual gearbox this would be fine. You see the threshold values for cold idle must be different. It can try to idle as high as 1600rpm when cold .... so pulls at the torque converter that drags the revs back to about 800rpm. What this means is the idle stepper motor is happy with the cold "idling" revs of 800rpm ...

If you throw it into park or neutral at traffic lights ..... The revs shoot straight up, and within 2seconds, the idle stepper motor drags it down to a nice smooth 6->700rpm idle... Like I said, it'd be fine with a manual gearbox.

So idle stepper motors doen't work that well with automatics... as the torque converter drag can mask a "high idle". Makes sense to me....

All fun right :)

seeya,
Shane L.

[PhilipA]

They are supposed to have a high idle when cold.
About 1200RPM.
Regards Philip A

[DoubleChevron]

They are supposed to have a high idle when cold.
About 1200RPM.
Regards Philip A

The torque converter isn't gong to allow it to get to 1200rpm without lots of dragging :) Yesterday I tried, and the revs shot straight upto 1600rpm when I put in neutral. The stepper motor immediatly kicked in and pulled the revs down to about 800rpm. Which was perfect given it was warm out, and the car had been running for a few minutes.

I'd believe 1200rpm for freezing cold start in the depths of winter would be about right.

seeya,
Shane L.

[loanrangie]

It wont drag in park or nuetral Shane.

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