Lumpy Idle??

[allante666]

Hi
2000 legacy 2.5. runs fine except for a lumpy idle. doesnt quite cut out but feels like its going to. if stood idling at a junction for any length of time its very slow to pick up again. (i mean like a few seconds rather than straight away).
Had new plugs. Its on lpg and although it idles slightly better on petrol its still not right.
Any ideas?
Thanks

[1996Battlewagon]

The firing order didn't get messed up when the plugs were replaced did it? I know it's simple, but it sometimes happens.

[allante666]

No it was like it before I replaced them. It runs perfectly ok when it's not idling so I don't think they can be in the wrong order. They are connected in the same layout as the coil pack sort of thing.

[allante666]

An update to this is that I found the hose had come off the PCV valve. Great! I thought, that'll be it. Nope it still does it, didnt make any difference putting the hose back on even though there was plenty of suction on the end of the valve so it must have been sucking in air.

[ouch1011]

I'm not familiar with the export models of Legacy, but is this a factory dual-fuel setup? Or some sort of aftermarket setup? LPG and Gas/Petrol require different tuning. I'm just curious to know about this setup.

I've seen/read alot about the SOHC models having misfire issues at idle only being caused by the cam timing being slightly (like 1 tooth) off. Have you had any timing belt work done recently?

[allante666]

Hi
Its an aftermarket lpg setup. They have a seperate ecu for the lpg injectors although it takes its engine data from the cars own ecu.
No, I havent had any work done as far as the cam belt goes but then again ive only just got the car. Its obviously had this problem before as someone has fastened a cable tie around the throttle linkage to stop it going quite as far back at idle and to try and increase the revs slightly.
You have a point though, its worth checking the timing. It does at times, particularly at low revs, feel a little bit retarded.

[02_Legacy]

It does at times, particularly at low revs, feel a little bit retarded.
The timing belt that ouch is talking about does not set the ignition timing. The timing belt rotates the camshaft, which moves the valves. The ignition timing is set by the ECU by data sensor imput such as MAF, TPS, IAT.

[allante666]

HI, yes, I meant the ignition timing. HOWEVER! I think I have found the problem. uponcloser investigation it looks like the previous owner has had problems with the idle. The TPS has been moved from its original setting several times by the looks of it. It has been marked but the mark doesnt correspond to anything! The 'idle' has been set by a cleverly placed cable clip to hold the throttle slightly open at tickover!
So..I got ecu explorer connected up and figured the best bet would be to reset the ecu. The timing was showing 10 btd at idle (if you could call it an idle) but even sat in the drive the engine felt retarded. I pressed reset and hey presto! the engine was instantly more responsive (the timing went up to 16 before top dead) and the idle was suddenly at about 1100!
I dropped the idle to 900 for now and took it for a short drive. even the gear changes were smoother and better. (its an auto). I suspect the idle is high due to the TPS being in the wrong place?. Ill drive it to work tomorrow to let it settle down an dthen have another look later.

So..my question is, How do I set the TPS to its correct position? and, what shoudl the timing be? (and how to set the timing, i.e. are there any sensors that need disconnecting before setting it with ecuexplorer? i presume i need it static rather than dynamic.)

All in all though a good nights work!

[allante666]

Hmm, might have spoke too soon! after 30 or 40 miles the idle seems to be slowing down and getting lumpy again.
Also, when travelling about 40mph and the revs at around 1500, just with a very light foot, there is a point that the engine feels like its bucking and missing, slightly more or less revs and it disappears. No CEL though. (the only error that showed up historically was a knock sensor but i figured that may have been because the timing was out?)

[Huffer]

The TPS is extremely finicky to adjust and really shouldn't be done without some prior knowledge.

Sounds like the prior owner had a problem with the idle, and attempted to fix it by adjusting the TPS manually. The real issue is that the Subaru ECU is an adaptive one - which means it is probably pulling timing to compensate for something else. The dual fuel is probably the source...

[allante666]

It may be but the dual fuel shouldnt affect it as Im running it on petrol whilst trying to make adjustments. The lpg ecu isnt in the equation. Do you think the tps is finicky enough to cause a really lumpy idle?

[Huffer]

Yep.

[allante666]

Ok, ill work on that assumption then! Ive found the instructions for the basic setting of the tps by measuring voltage at a couple of terminals on the ecu. I take it that whenever I change any setting such as that I should reset the ecu every time and then take it for a drive yes?

[Huffer]

Yep, but it will take a few drive cycles for the ecu to adapt and show if theres any error.

[allante666]

Ok thanks. do you know what constitutes a 'drive cycle' and how many it requires before its finished doing what it does?

[Scimitar]

A drive cycle goes something like Start, Warm-up to operating temperature, Shut down, Cool down. I believe with OBD II, it's usually 3 cycles, but don't quote me on that.

[allante666]

ok well tonight i set the tps according to the manual (alter it until you get 500mV on two ecu terminals). I then reset the ecu and took it for a 2 mile drive with some stop start driving. Ill run it over th enext few days and see what happens, Idle is a lot better and doesnt cut out but still a little lumpy. Is there any way of checking the cam timing without taking the covers off the belt?

[Huffer]

Good stuff! You'll really need a timing light unless the ecu software can give you parameters to work with. Sounds like you have a couple of things going on.

[allante666]

I have a timing light but the software also gives a live readout. I'm just a little suspicious that maybe someone has changed the cam belt and got it a tooth out. I just wondered if it was possible to check the cam timing without taking off the front covers. I don't want to spend hours blaming the ecu etc if there's a simple mechanical reason.

[Huffer]

well if you want to check the mechanicals, then you have see them...

[httrdd]

I had a lumpy idle on my engine swap and tried everything to fix it. My water pump went and during disassemblfy I found out my crank timing was off 2 notches. After changing the pump and resetting the timing it ran perfect.

[allante666]

yeah this is what im sort of leaning towards. I guess if the cam timing was off slightly the ecu would try and compensate with the ignition timing, hence why after a reset its ok for a few miles then starts getting back to how it was.
I think as soon as i get a chance im going to have to have a look just for my own peace of mind if nothing else.
Was yours ok other than a lumpy idle? at speed mines ok, it will happily manage 100mph and acceleration is pretty much ok. probably a little flat if anything under 2500 rpm

[httrdd]

Yep that is what mine was doing. It would surge at a stop.

[allante666]

Mine never surges, it just gets slower and lumpier and if I dont give it a few revs it will cut out.It will start again ok but its a pain, specially as its an auto. Another thing that makes me wonder about the belt is that when you floor it, every time it changes up a gear you get a little crackle from the exhaust, like you would get on a rally car with bigger lift cams . It might sound good if I was a boy racer but im a bit too old for that! Id rather have a smooth idle!

[Huffer]

Check your timing belt, and tensioner. Any more than 1 inch slack and you'll skip a tooth or two.

You should also clean your MAF sensor, and the Idle Air Control Valve on the throttle body. Those two things will contribute to a stumbling idle.

[allante666]

I've already cleaned the idle valve. Does it set itself up when you put it back? There's no adjustments you have to make is there? I don't have a MAF I assume I have a MAP instead.