High-pitched whine, jerky acceleration, rough idle, check engine light

[211]

For the last couple months I’ve had an intermittent CEL. I’ve pulled the code numerous times (buddy has an OBDII code reader and laptop), it’s always the same; KNOCK SENSOR. It’s intermittent so the CEL will go out for a week or so then come back on for a couple days, then for some reason just go out for another week or two…

 

…but recently I’ve been experiencing some other issues.

When I accelerate there’s a high pitched ‘whistle’ or whine right around 4k, this happens in all the gears and only in the upper RPM range. At first I thought it was one of the belts but they seem pretty tight; it almost sounds like it’s sucking air in from somewhere like a crack or split in a boot or something, but I’ve checked and I don’t’ see anything obvious. Anyone else ever experience this?

 

Also (and this may or may not be related to the above), acceleration has not been so smooth. The car is noticeably jerky and the idle has been rough.

 

This is a 2000 OBW 110k miles. I replaced the plugs at 103k (when I did the timing belt, W/P, idlers, belts etc). Plug wires are OEM and I think they were replaced during the car’s 60k mi major service interval (previous owner, done at dealership).

My first hunch is the plug wires but how do you know when they need replacement? There’s no service interval in the Subaru Maintenance Schedule for plug wires, just plugs.

I realize I need to replace the knock sensor, but these little buggers aren't free! 80$ for one of these and I'm not sure it will make the car run smoother.

Need to prioritize at the moment.

Edited May 21, 2009 by 211

[porcupine73]

Sometimes whistle is idle air control valve or one of the vacuum lines unhooked. I have an '00obw and I will tell you from experiments with the knock sensor that it can nearly make the engine stall at times and give it nearly no power.

[211]

I have an '00obw and I will tell you from experiments with the knock sensor that it can nearly make the engine stall at times and give it nearly no power.

 

Interesting! Maybe I should focus on that then for now. Needs to happen anyway.

It's just that the knock sensor CEL has been intermittent for quite a while and the other symptoms mentioned are just now appearing.

[OB99W]

You may have more than one problem causing the symptoms you've described, but you should deal with the the knock sensor first. Assuming the knock sensor is properly mounted and connected, the code almost always is caused by a cracked sensor. When the ECU determines that the knock sensor is bad and sets the code, it also goes into a ''limping'' mode that retards engine timing (since the ECU can't reliably tell if knock is actually occuring). That will definitely affect performance, and might at least partially be what you're experiencing.

 

While I can understand your concern that a new sensor might not resolve the problems, you may be paying for it anyway. The engine won't run as efficiently as it can if ignition timing is retarded unnecessarily, so a bad knock sensor will somewhat reduce gas mileage -- your out-of-pocket expense for the extra gas will eventually catch up with the cost of a new sensor, but if the sensor hasn't been replaced you'll still have the problem.

 

I'd suggest dealing with the knock sensor, and then seeing what symptoms remain. By the way, sometimes ''whistles'' are caused by exhaust leaks.

[unibrook]

OBiwan99W speaks wisdom. Do knock sensor first, since you are getting that exact CEL code. If after that, you are getting hesitation under load when the engine is warm, I suggest replacing your front 02 sensor if it hasn't been done in the last 40k miles.

[211]

Okay I'm back.

Replaced the knock sensor (dealer part). Went to check/clear the CEL code and found a Misfire Cylinder 4 code present along with the Knock Sensor I knew was already there.

So that explains the jerky acceleration and rough idle, but now I'm wondering if the misfire is what caused the knock sensor code to trip or if the knock sensor failing caused the ECU to go into limp-mode and thus cause a misfire in cylinder 4.

Either way the car still runs like crap but with the ECU just being cleared it's still going through its learning curve.

 

Any ideas is appreciated

Thanks

[bdecriscio]

I'm a little confused! On other posts regarding bad knock sensors, it seems that most posters say that a bad knock sensor code indicates just that, not a knock detected. My assumtion was that if you didn't have symptoms of knock or pinging then there was no retarding of timing, just that the risk was the computer would not compensate if you did have engine problems such as knock or pinging. Set me on the right path, I'll need to replace my sensor sooner rather than later. (not easy to do since someone previously put in an after market one with very little wire left for me to work with). Thanks, Bob

[211]

I'm a little confused! On other posts regarding bad knock sensors, it seems that most posters say that a bad knock sensor code indicates just that, not a knock detected. My assumtion was that if you didn't have symptoms of knock or pinging then there was no retarding of timing, just that the risk was the computer would not compensate if you did have engine problems such as knock or pinging. Set me on the right path, I'll need to replace my sensor sooner rather than later. (not easy to do since someone previously put in an after market one with very little wire left for me to work with). Thanks, Bob

 

That was sort of my understanding too, which is why I went so long before replacing my knock sensor. Ultimately my car did start to run rough which prompted my original post. I should've pulled the codes again because I bet the misfire code cropped up later and is the REAL culprit for why the engine is running so poorly.

Now I'm 80$ into this for a new knock sensor and the car still runs like poo. I need to know what to do next because blindly throwing money at this thing is not an option.

 

Oh yeah, and I just noticed BOTH my CV axles are shot (spewing grease); but that's for another thread

[ron917]

Your knock sensor was broken, so the money you spent on it was not wasted. The knock sensor code is thrown ONLY if the knock sensor is defective. And yes, it can be intermitant.

 

Knock or predetination is a normal operating condition. It happens often, whether you hear it or not. Under load, the engine is running on the hairy edge of predetonation. The knock sensor tells the ECU when it happens so the ECU can take appropriate action to prevent engine damage. If the knock sensor is defective, the ECU goes into a limp mode (retarded timimg) to protect the engine and the car has no power. And yes, the limp mode can intermitant, also.

 

The miss and other symptoms you are experiencing now are a different problem.