[alien]

Alright, try figure this out...

Went for a drive at lunch – cold idle was 1400. No more than 30 secs later i’m at a set of lights and it’s at 1100. Take off, drive a few hundred metres, stop – 1400. Drive another 1km, stop, 1100. Head back, stop at lights, 1400. Pull back into work, stop – 1100. Disconnect IAC plug – 2500+ (didn’t look) – plug back in – 1100. Repeated with same results.

Now it gets interesting..

Driving home: Cold start – 1400. Lights – 1100. Lights – 1400. Lights again – 1400. Drive up the freeway, stop at lights again – 1400. Intentionally short change gears and taking it very easy before next stop – 1100. Push up to 5000rpm in each gear to 4th, stop – 1700. Take it easy for a few hundred metres, stop – 1100. Push 5000rpm in all gears to 3rd, stop – 1800. Take it easy a few hundred metres, stop – 1100. Redline it in 2nd, stop – 2000.

Then, after a quick workout just now with the battery disconnected (intending to reset ECU), i started it up again and it went right to 1400, then in about 5 seconds dropped to 900. It idled spot on until it was at temperature again, then i turned it off, back on again, 1400 and dropped to 900 in a few seconds. Then i gave it a rev to 3000rpm and came off the pedal and it’s idling at 1400, then takes a few seconds before it lowers back to 900.

My best guess is that a sensor must be malfunctioning??? It seems like after it’s had revs it wants to hold them. Not sure what sensor is responsible for that though? And i’ve got no misfire or lack of power?

... Thoughts?

[Buckman]

What engine mate.

[rexhunta]

Vacuum Leak ?

[MrRocky]

Swap throttle body and tps sensor
Alot of the time swapping just the sensor alone doesnt fix it.
You may also be able to clean the throttle body but you will have to be thorough and remove it from the plenum

[alien]

TPS makes sense, i was thinking something like O2 given it idles high after having more revs but there's no other symptoms.

Buckman - for all intents and purposes, call it a g13bb jimny motor (it's got a g16b bottom end and injectors on it).

[fordem]

I've had a defective PCV valve cause symptoms very similar to those, but on a J20 engine - the PCV valve was broken and allowing so much air into the system that the IAC could not compensate - essentially any "vacuum" leak allowing air in can cause it.

[Buckman]

Yeah could be pcv sticking could also be the engine coolant temp sensor failing telling the ecu that the engine is cold when it's not. Measure the resistance of the ect sensor when engine is bone cold, get it up to operating temp and measure resistance again.

[redvitara]

What about the coolant hose to the iac?
I had idle probs when i first got mine & it turned out to be this hose that was restricted by rusty gunk.
Redvitara

[alien]

Thanks guys! I'll post back what it ends up being

[alien]

IAC internals in the throttle body were all gummed up. quick clean and its good as new.

[shandy92]

Easy fix then, did u end up getting the head done?

[alien]

Yeah all done and runs great. I believe the gunk in the throttle body was related to the gasket going, cos it was fine beforehand... but then it doesn't make sense being where it is to suddenly get jammed up. Must just be coincidence.

[shandy92]

Oh cool, for how long tho???? Still keeping ideas open for other engines? Yeah its a bit strange, engines do weird things sometimes.

[alien]

Well, I ended up sticking with the cheap/easy option for now. Not exactly swimming in cash to get a new engine, so hopefully this new gasket stands the test of time.

Down the track i'd definitely look into something newer to go in there though. Next year there's a Vitara 1.4 Turbo being released - 103kw / 220nm.. that could be fun =)

[shandy92]

Nice, lets hope they fixed the block issues from the jb24 and g16 and havent transfered them to this new one.

[fordem]

Research direct injection & intake valve "coking".

One of the problems with direct injection engines, especially those that use EGR systems has been heavy coking of the intake valves - soot from the EGR system gets deposited on the back of the intake valves - on MPI engines, the gasoline in the incoming charge washes the soot into the combustion chamber, but on direct injection engines there is no gasoline in the incoming charge and the soot deposits build up and bake on.

[alien]

So it will have a 3 year warranty, at which point the delearship you bought it from will slog you with an engine rebuild to replace the valves?

[Seth2013]

correct!! - but you have to think of all that money you saved on fuel with your new direct injection engine, that will surely cover the cost of the rebuild

[Marko_SJ]

Or just give it a clean once in a while and block the EGR.

Edit: which I've done neither of in 5ish years and my DI engine is running fine.

[fordem]

Would you really notice the gradual decline?

One of my vehicles has a Mitsubishi 4G93 GDI engine (the first GDI engine to be used in significant numbers) and the crap that accumulates in the intake quite literally has to be seen to be believed, and the difference in the way the vehicle runs, after cleaning is equally astounding, and please bear in mind, I haven't pulled the head and done the valves or the valve throats, and that's where it "bakes" on.

I also own a much more recent GDI engined Kia (a 2015 Sportage with the 2.4 litre engine) which I am not going to be taking apart to inspect any time soon - with a 10 year, 100,000 mile powertrain warranty, it's going to be Kia's problem. The decision to go with Kia was made based on warranty & road side assistance, rather than the type of engine, this car is driven by my daughter and dad's not nearby to assist when needed - I fully expect it to be sold before the powertrain warranty ends.

[Marko_SJ]

fordem wrote:

Would you really notice the gradual decline?

One of my vehicles has a Mitsubishi 4G93 GDI engine (the first GDI engine to be used in significant numbers) and the crap that accumulates in the intake quite literally has to be seen to be believed, and the difference in the way the vehicle runs, after cleaning is equally astounding, and please bear in mind, I haven't pulled the head and done the valves or the valve throats, and that's where it "bakes" on.

I also own a much more recent GDI engined Kia (a 2015 Sportage with the 2.4 litre engine) which I am not going to be taking apart to inspect any time soon - with a 10 year, 100,000 mile powertrain warranty, it's going to be Kia's problem. The decision to go with Kia was made based on warranty & road side assistance, rather than the type of engine, this car is driven by my daughter and dad's not nearby to assist when needed - I fully expect it to be sold before the powertrain warranty ends.

If I wasnt so lazy to work on the thing, I probably would pull it apart to have a look.

People with modern-ish diesels and EGR get the same problem. They have work arounds, if enough of these petrol ones start going, people will discover a work around, which I suspect would be quite similar to the diesels.