legacycentral bbs

Yes, finally, and it was the simplest of ideas... motor mounts. I put my bottom ones in yesterday and found it to be a big improvement, and since I didn't have time to do the dogbone yesterday, I just did it about 30 minutes ago after I got off work... and the hesitation problem has for the most part vanished! I presume that so much power was being wasted by moving the engine around that the car simply didn't have enough power going to the wheels...

I think I'm still going to put an updated knock sensor in there anyway, just for good measure, since it's not that expensive anyway....

But I have finally found the cure, and all this time I thought it was something more complicated!

Cool!

Is it possible that the vibration due to worn motor mounts could make the knock sensor register a false positive?

Very cool Michael,

Glad this worked for you. If I have time I may replace mine for kicks & giggles. Probably will put sti ones in.....and I'll have to look and see about a new dog bone.....not sure if it'd be worth replacing that.....we'll see.

vrg3 wrote:Cool!

Is it possible that the vibration due to worn motor mounts could make the knock sensor register a false positive?

That is my exact theory, that's why I'm going to replace the sensor anyway...

Sounds like you might be on to something I wonder if the engine could have moved enough for some part of the motor or the mounts to hit something? How about the hesitation that some people have found at about 5300- 5500 rpm I have a theory on that one ( and a cheap fix if I am right)but haven't had time to check on it. Another thing that might point to you being right is that I have never had the low speed hesitation but have the STI tranny mount and new Turbo engine mounts.
AL(CO)
al@iwtu.net

Well, actually, now that I think about it, the engine vibration could also result in worn-out wiring harness connectors. Weird readings from pretty much any sensor could result in hesitation. Vibration over time can just wear out the springiness in the connector terminals, and then when it shakes hard it can cause noise in the signal.

Since the clunking noises that once drove me bonkers are now absent, I do believe the engine was hitting something...

vrg3, please don't tell me that the connector from the wiring harness to the knock sensor has been vibrated to uselessness, in which case i would have to put a new connector on and until I did, replacing the sensor would get me nowhere...

I'm sorry, dude...

It's not necessarily true, though... Even if the connectors are damaged, they're not vibrating nearly as much now so they'll still work better even without being replaced. A cheap way to improve it a little would be to take a look at the contacts, and if they have any dirt or corrosion on them at all, clean them off. I'd start with contact cleaner, and maybe even a little acid or something if there's oxidation. The connectors can't be completely useless.

I think the harness connection to my IAC valve might be bad... My car's had a bad idle since I bought it last August; the previous owner replaced the IAC valve with a brand new one right before I got the car. I checked the ECU codes, and there was an IAC valve code. I figured that the dealership that replaced the valve never cleared the code, so I cleared it. The other day, while driving, I noticed the idle get weird; it stumbled and then bumped up really high, and the CEL came on. It went away in a little bit, but the same thing happened again a little later. I think maybe the ECU's connection to the IAC valve might not be good. My mounts are really worn out, too, I'm sure, since the motor vibrates like mad, so that's probably not helping. I don't think this alone is 100% responsible for my bad idle, too, so there's probably a vacuum leak or something also bringing trouble to the mix...

Well, I checked my connectors today, the sensor connector doesn't look great, but the wiring harness connector does . And when I put them back together, they seemed to connect with a tight, reassuring snap, no wiggling between the two. vrg3, I can see what you're saying but I think most of the wires to the various sensors have enough slack in them to prevent this...

Anyway, I just ordered a new sensor from www.subaruparts.com (thanks for the help ciper), and I'll report back after I put it in...

Well, irrespective of slack, the whole thing vibrates a little, and the metal-against-metal contact at the terminals has the potential to start corroding... What exactly do you mean when you say the connector didn't look good on the sensor side? Since you've got a positive engagement with the connector housing, any trouble ought to be fixable by cleaning the pins, unless they're really far gone.

Of course, the new sensor will have new pins in its new connector... :)

Okay, knock sensor has been replaced...

"and the hesitation problem has for the most part vanished!"
Note that I said for the most part, I still was having a tad in 1st gear, but I only noticed that after I made a big brouhaha that I had fixed it ...

Now it is fixed completely, save for when the engine's cold, but I try not to expect too much from it when it's cold...

It also helped my idle issue a whole lot, I don't really understand why, since detonation shouldn't be an issue at idle, but hey don't ask questions, just be happy it's fixed...

I think that it's still off a bit because I screwed around with the TB stopscrew and when I did I scraped off the red marker silicone whatever-it-is, so it's not at factory position, and I think the ECU's mad at me for that...

But, finally, my car runs like it should, so I am very very happy