JedMeister

Ok. Sounds like I'll just leave it stock then. Thanks again for your input.

Just wanted to report back again. My Subi is going so well now! No doubt about it at all; that knock sensor was rooted! It still brings a smile to my face when I put my foot down and it takes off! It's just been a pleasure to drive over the last fortnight! I still haven't hit it with a torque wrench yet, but the unstable idle seems to have fixed itself. Perhaps now it's running a bit better it has cleaned itself out a bit, although I still plan to give the throttle body a good go (when I get around to it). Now it's going a bit better, I've been thinking about perhaps getting a higher flow air filter and perhaps squeeze a little more out of it... Any suggestions on good ones? Also if I do that are there any other considerations? Or can I just fit it and go? [Guess I should probably start a new thread...!? Or perhaps just have a good search...!!]

Knock sensor arrived Friday and I put it in. The old one didn't have any visible damage at all (some have mentioned there is often cracks in the plastic covering) but it did had quite a bit of white corrosion on all the metal parts (between the senor and the engine, through the hole the bolt goes through and under the head of the bolt). And it was very tight (although perhaps that was because of the corrosion?) I replaced it and when bolting the new one in, gave the ratchet about a 1/3 turn after it seated. And it has made a huge difference!! It's still not perfect, it has a slight hesitation for a moment around 3k-3.5k but the +/-500RPM flat spot is gone!! As it has a slightly unstable idle at times I am hoping that perhaps if I give the throttle body a good clean I can clear up that and the slight hesitation. I have sprayed carby cleaner through the throttle body before but my reading suggests that I need to get in there with a toothbrush and give it a good scrub out to do a proper job... Over the weekend I gave it a pretty good workout. Myself and 3 mates went for a bushwalk which required about a 250km drive and it ran so sweet! It's never run that well carrying that much weight (probably equivalent to about 5 adults). So I think we can safely say that the knock sensor was the main issue... As for the OBDII adapter. I was using it with Torque (Android app) both on my phone and on my tablet. It connects fine (via bluetooth) and scans through all the protocols (and all the lights on the unit flash as it does it) but says that it can't connect to the ECU. My Dad has a later model Subaru Outback so I'll give it a try on that and see how that goes. Thanks again for all your help guys!

Thanks for the tips, I'll borrow a torque wrench then...

Yeah I've done a visual check and it looks ok but I figure with something like that a visual check is never enough. As for the flat spot, it's had it as long as I've owned the car (~4-5 yrs) but I just got used to it. Different fuel has never made any noticeable difference in any way, shape or form. Although I haven't tried any other fuel in since it seems to have got worse (I only hooked up the cheapo OBDII thingo night before last...) Once I put the new knock sensor on I'll try again. BTW, lots of people say that the knock sensor needs to be tightened to the correct torque, is that important?

Here in Australia 'Regular' is 91, 'Premium' about 97-98 (depending on where you go) and I have seen some others at around 100(+/-). I use Premium+ in my motorbike and you can notice the difference in that, definitely goes better/smoother/more power (I guess it comes down to power-to-weight). But never noticed any difference in my Subi. On a sad note I don't think my Subi is OBDII compliant Like I think I said above, I got one of those cheap eBay bluetooth OBDII connectors and no joy (won't connect to ECU). I guess it could be a faulty one though... My car definitely has the plug, but when I pulled it out, it's only got a few wires in the back of it. I guess I need to test the eBay bluetooth OBDII connector on another car. Although I don't know if it's conincidence or not, but ever since I had it plugged in and spent some time trying to get it to work, the flat spot has been really bad when it's cold and right down around 2,500 RPM (if you recall originally the flat spot was much less noticeable when the car was cold, now it heaps worse - once the car warms up it's like it was before). Do you think it's possible that just plugging in the cheapo OBDII connector has caused this? Or is it just coincidence do you reckon?? Still waiting on my knock sensor to arrive...

Just have a standard air filter. I have read that a high flow air cleaner is the cheapest, easiest way to get a bit more go out of the Subi. I have run it on Premium ages ago but didn't notice any difference at all. Still waiting on my new Knock Sensor to arrive, shouldn't be too far away.

Thanks heaps again guys. I'm blown away with how helpful you all are! Wish I'd found this forum a few years ago and then perhaps I would've fixed this issue ages ago... I guess it isn't fixed yet but I got a good feeling... @bluedotsnow - Thanks for that link, that is super excellent! It doesn't specify Australian models, but from what I can gather the Aussie models are the same as the European ones. And it turns out (assuming that is how it is) the knock sensor on mine is the AA070 (like I thought) which is the same part no as the US '99-'03 2.5lt (as advertised on the eBay listing I was thinking of buying). @Fairtax4me - Thanks for your reassurance! @mikaleda - Thanks for your suggestion, but reading on other threads/forums regarding knock sensors, it seems that testing knock sensor resistance isn't really enough, especially for a problem like mine (like Fairtax4me said). Apparently the only reliable way to test a knock sensor (or any other part) is to test it while the problem is showing (ie for me - while my car is experiencing the flat spot). After talking to a mate of mine (bit of an electronics whizz) he reckoned the only way to reliably test it would be using an oscilloscope on the knock sensor with the car on a dyno. That way the flat spot could be recreated while the signal the knock sensor is sending back to the computer could be monitored. Long story short, it's cheaper and easier for me to just buy the knock sensor and hope for the best, so that's what I'll do. Thanks again everyone for all your input. I've just bought that US part and will put it in as soon as it arrives. I'll try to remember to post back to let you all know how it goes.

Hmm... Been having a look on eBay for a knock sensor and it seems that there are 3 different ones. The AA031 (which I'm pretty sure isn't the right one - it's for older Legacy/Liberty models), the AA061 and the AA070. I've read in places that the only difference is the plug. Now from the (poor eBay) photos that I've seen the plug on the 061 and 070 are the same and the 031 is different. The main difference between the 061 and 070 is that the 061 has a non-detachable lead that plugs into the wiring harness (like this) and the 070 has a short lead that can disconnect from the knock sensor itself (like this). I've had a look and mine looks just like the 070 (has the detachable lead) and the cheapest one I can find (inc postage to Aust) is this one but it says it's for "2.5L 1999-2005" which is obviously not what mine is. Do any of you guys have any idea about this? Otherwise I might just shell out the ~AU$30 and try my luck.

Thanks again guys, I really appreciate the input. @1 Lucky Texan - I neglected to mention mileage it's done nearly 220,000km (~138,000mi) so I'll try & find out if it has hydrologic or solid lifters. @mikaleda - Yeah it's a bluetooth one so you can connect to it via a laptop or smartphone (according to my googling there's a few different apps that'll do it). @Fairtax4me - Thanks for clarifying. No CEL so there'll be no codes... So I think I'll get on eBay and get that Bluetooth connector & I'll also get myself a new knock sensor & see how I go. Thanks again guys.

You guys rock! Thanks for the rapid responses. After my googling I was thinking TPS or Knock sensor seemed like possibilities. Just thinking though, wouldn't a dodgey TPS tend to cause the hesitation regardless of whether it was under load or not? (Going by the name, it reports throttle position back to computer...?) @1 Lucky Texan - By valve adjustment, do you mean valve timing? If so, I would assume that that the timing belt replacement (and readjustment of the valve timing), or is there something else I'm missing..? Actually the more I think about it, the more likely knock sensor seems to me. Or perhaps it actually is knocking? (Someother fault causing the timing to be to too advanced or something). I have never heard it knock, but the flat spot occurs under the same conditions in which it would be knocking if the timing was too advanced (and it didn't have a knock sensor). @1 Lucky Texan - Excuse my newbness... but how do I find out 'are there any codes stored?' I'm assuming I'll need to connect to the computer somehow. After a bit of a google and I came across this on ebay. Is that what I need (connected via bluetooth to laptop or smartphone)? Or is is there a better way to go? Can I just disconnect the knock sensor and see what happens, or will I need to get a replacement to test if that's the issue? Guess it's probably worth checking the MAF sensor not sticking and run the multimeter over the TPS too

Hi all, I have had my Subi for a few years now and I love it! It's a 2lt '98 GX Liberty (Legacy in the rest of the world) Wagon. But it has one minor issue, For as long as I've owned it, it has had a flat spot around 3-4000RPM when under load. I didn't notice it initially when I test drove it, but within a few weeks of buying it I noticed it. It's most noticeable on the open road - under heavy acceleration, like up hill or overtaking. It accelerates up to the flat spot fine and once over about 4k (sometimes as much as 4.5k). Within the flat spot it just has no go. Whilst it is generally between about 3.5-4k, sometimes it happens as low as 3k and doesn't resolve until 4.5k (sometimes even closer to 5). A couple more things I have noticed about it: - Seems much less noticeable when the car is cold (air temperature doesn't seem to affect it at all) - It's always much better (for at least a few days-weeks) after it has new spark plugs. The guy I bought it off said that he had replaced the coil pack recently (and I have no reason to doubt him, but no proof either). I recently had the timing belt done and the mechanic siad that the old belt was one tooth out and I hoped that that may have been the issue but it wasn't... The only other issue (which may or may not be related) is that the idle is a little unstable sometimes. I had just got used to it but since I thought it may have been fixed it has been really bugging me... I've had a bit of a google and this is the only post I found that sounds the same as what I have. Unfortunately there is no clear answer there... Anyone got any ideas? Even ideas on how to properly diagnose it? Thanks in advance.