RESOLVED - Ssssssssick Q. The dreaded Knock Sensors

[oldmako]

Well after 3 years and 70,000 pretty much carefree miles my car has decided that it needs some TLC. It recently developed an occasional misfire at idle. It manifests itself when at a red light with the transmo in Drive. Oddly (or not) enough, it doesn't misfire when in Park, and it doesn't misfire after a cold start, only after it has achieved normal operating temperature. The car now has 175,000 miles on it.

The engine runs perfectly at 2500ish, which equates to about 75mph. I say this because I use the car on the interstate 98% of the time and it's smooth as glass on the highway. It also runs fine at WOT.

Previously it would "occasionally" misfire but this was always cleared up by some BG44k and a few tanks of the best gas I could find.

According to my made in CommieRedChina by a guy earning 3 dollars a day U380 El Diagnosto Supremeo Gizmo the following codes:

P0325 Knock sensor 1 circuit malfunction Bank 1 or 1 Sensor
P0330 Knock sensor 2 circuit malfunction (Bank 2)

Supposedly the knock sensors were replace before I purchased the car in 2008. It has run pretty much flawlessly since then.

I had thought that my coil(s) were getting long in the tooth because of the "stumble" threads but this is pointing the dirty digit at something else.

I would have thought that the KS were essential to higher RPM operations and more or less inert at idle, but my car is behaving in the opposite manner.

I was hoping to get a code for a specific cylinder which would have allowed me to just replace an individual coil. That would have been a much easier repair. But now I am flummoxed, confused, inverted, muddled, unsure, and in a general state of stupor.

So, tossed out for the Qmasses, what in the hail am I 'posed to do now??

Obsequiously awaiting your thoughts. Till then I will remain in humble servitude with wrenches at the ready.

Stay thirsty my friends!

[qship96]

IN MY EXPERIENCE, on my 96Q, going from defective knock sensors to new made VERY little difference, probably un-noticeable for the average driver.....tip in acceleration was snappier after replacement- but bad sensors caused ZERO stumbling or poor idle,zero- MPG did not change either.......look beyond the knock sensors for the root cause of your issues{but good idea to eventually replace both knockers after verifying with multimeter for continuity and ohms }

[oldmako]

Thanks for that. Your experience makes perfect sense to me and validates the reason I posted. Knock sensors affecting idle makes no sense to me, but I am just a lowly shade tree wrencher.

For now, the car is driveable the way it is. I'll give it a few more miles and recheck the codes. Hopefully something will pop up which makes more sense and is an easier fix.

[subtle_driver]

knock sensors only throw the ecu into a different timing/fuel map only on hard acceleration so there is less detonating. If they are bad the ECU permanently stays in this de-tuned state until the code is cleared and the knock sensors are good.

I agree, the problem you are having has nothing to do with knock sensors. You can sometimes trigger the knock sensor code with the misfire you are having. My friend had a knock sensor code triggered by a broken motor mount. It was metal to metal contact and caused a horrid vibration and it triggered the knock sensor to think it was detonation. I also have seen loose knock sensors that cause this too. And it can be caused from high temperatures and cheap or low grade gas.

But ya, try doing a compression test when the car is warmed up. It was a pain to diagnose. I also have seen Q45's with low compression on a couple cylinders that caused a missfire.
I have seen a 97 Q45 that had a bad injector that only acted up at certain times.

BTW, the china scanner may not get all the codes. You may have more codes in there, You need a consult to be 100% sure. I think Consult 2 is the best option for your 99?

[oldmako]

Three cans of that fancy chevron (??) techron rfuel system cleaner and about 1000 miles of Emmerson Fittipaldi style driving and my stumble 'be' gone.

I suspect that the KS codes were brought on by an earlier condition, perhaps even the stumble. At any rate, food for thought if your Q is suffering and you don't feel like dropping a grand and 3 days under the hood chasing the wrong gremlin.

178,000 and with the new Michelins it feels like a new car on the highway. Sure it has a few issues (shocks are overdue) but I am still thrilled with it. I'm going to take it to 250,000 and bury it.

Stay thirsty my friends.

[chris2020p]

Why only to 250,000 miles? Take it to 500,000 miles and more...better yet run it forever!

Also thanks for using the "RESOLVED" title.

[oldmako]

250K because I am the cars second owner and it has a few minor issues which I don't want to address. Maybe I'll go 300K. We'll see.

The bottom line is that the car is presently worth so little, and the repairs and parts are so darn expensive, that at some point I am going to just throw in the towel. Plus, there are so many other cars which I am interested in, hell I'll take an M45 or something else. Of course, I could change my tune, or get struck by lightening, or abducted by aliens, or wind up in the funny farm. Who knows.

Right now it needs shocks, a new windshield, a pax front seat, paint work, new console wood trim, etc. I got the car for next to nothing, but I may open the wallet a bit wider next time and get something in pristine shape. Something that would be more worthwhile getting anal about its maintenance and keeping it forever. I like the 850 csi BMW.

[paranoidjack]

Stay thirsty my friends.

Lol, just got home with a box of brown.

[chris2020p]

250K because I am the cars second owner and it has a few minor issues which I don't want to address. Maybe I'll go 300K. We'll see.

The bottom line is that the car is presently worth so little, and the repairs and parts are so darn expensive, that at some point I am going to just throw in the towel. Plus, there are so many other cars which I am interested in, hell I'll take an M45 or something else. Of course, I could change my tune, or get struck by lightening, or abducted by aliens, or wind up in the funny farm. Who knows.

Right now it needs shocks, a new windshield, a pax front seat, paint work, new console wood trim, etc. I got the car for next to nothing, but I may open the wallet a bit wider next time and get something in pristine shape. Something that would be more worthwhile getting anal about its maintenance and keeping it forever. I like the 850 csi BMW.

Sounds good.