2002 Impreza 2.5TS: Problems After Wire and Spark Plug Replacement

[Degree210]

 

Here is the story: My 2002 ran into a misfire in cylinders 1 and 2. The car had been occasionally stuttering on accelerations, however, the check engine light would not come on after a stutter, just after hitting high rpm on the highway it would start flashing and stop (above 3k). I was told by a few people to change the wires and I figured I had no idea when the plugs were last changed (used car new to me) so I might as well change those while I am in there. The change of wires and plugs go on without any problems, however, upon starting the car, the car is immediately revving up to around 2000rpm. I figured to take it for a test drive see if it righted itself, which it did not. While I was driving I noticed that the car drove better than it had before, smoother ride, felt like it had more power. I also noticed that the car seemed to always have a little bit of gas on. From a stop, with no gas pedal, the car would begin to accelerate. I was able to let it get to around 25-30mph very slowly, yet all on its own. Upon arriving to a stop at about 10mph (this happens every time), the car would jut forward a bit and the rpm would go up by about 250 for a split second then come back down, almost like I put down the gas pedal. Upon sitting idle in drive the entire car begins to vibrate, with the rpm at around 1100, seeming like it was about to stall. Brake lifted, car goes back to normal with no vibration. Father in law who has owned and fixed many Subaru motors said to keep the car on idle in park for around 20-30min. At about 20min, the car started pulsing the rpm and when gas was applied, simply continued its incessant pulsing instead of revving up. We tried to have the car relearn idle, going through the whole process of disconnecting the battery and then the long series of steps after to no avail. Still all the same problems. Drove it to work about 50mi total, on the way back, the knock sensor wire got disconnected and broke, and I lost a ton of power, the car was then even having a ton of trouble going up hills. The Replacement Parts: I replaced the wires with NGK RC-FX58 wires, and the plugs with NGK 5464 BKR5EIX-11 Iridium IX plugs. The gap on them is 0.044". Now what? I do not know where to start looking for solutions, from what I see and hear, there are no vacuum leaks and the throttle control wire was untouched and is not pulling on the throttle at all until the pedal is down. Any ideas? Thank you in advance for reading this far, sorry it was so long... Just making sure all the information is there.

Edited December 8, 2021 by Degree210

[lmdew]

Is the IAC hose on.  About 1" dia going from the air box to the IAC.

I always go with NGK Copper core plugs and NGK or Subaru wires.  If this all started after the maintenance double check all connections.

[heartless]

basic copper core plugs are all that is required by that car (owners manual lists BKR5E-11 or BKR6E-11), you gain nothing by using the iridium plugs except a lighter wallet

gap is a little bit high.. spec is 0.039 - 0.043 - i usually set mine closer to the lower end.. typically about 0.040 - gap will slowly increase with age and wear...

the plug wires you purchased are the correct set for that car, just make sure they are fully seated at both ends.

and definitely check all the plumbing to the air box, and all vacuum lines..

Edited December 9, 2021 by heartless

[Numbchux]

I believe that engine should be speed density (MAP sensor, no MAF), and therefore shouldn't be that sensitive to leaks before the throttle body. IAC is built into the throttle body, no separate hose for that.

 

What did you disconnect/remove to access the plugs? I generally remove the washer reservoir on the LH side, and airbox on the RH. The throttle cables (main and cruise) run right over the plugs on the LH side, you sure you didn't shove them out of the way and they got hung up somewhere? 

Any trouble codes? Confirmed, or pending? What does the TPS signal and coolant temp look like?

How did the knock sensor wire get damaged? Was there something tugging/chafing on it? The coolant temp sensor is in that area, too...

 

 

The symptoms kind of sound like a sticking IAC valve. Although I don't think I've ever heard of that on these before. And the timing would have to have been a complete coincidence, which is unlikely.+

 

I do agree that Iridium is not ideal for your car, but shouldn't cause any problems.

Edited December 9, 2021 by Numbchux

[1 Lucky Texan]

no oil on the plug wire boots?

double check ground connections, if the knock sensor wire was broken, maybe other wiring was as well?

[Degree210]

5 hours ago, Numbchux said:

What did you disconnect/remove to access the plugs? I generally remove the washer reservoir on the LH side, and airbox on the RH. The throttle cables (main and cruise) run right over the plugs on the LH side, you sure you didn't shove them out of the way and they got hung up somewhere? 

Any trouble codes? Confirmed, or pending? What does the TPS signal and coolant temp look like?

How did the knock sensor wire get damaged? Was there something tugging/chafing on it? The coolant temp sensor is in that area, too...

 

The symptoms kind of sound like a sticking IAC valve. Although I don't think I've ever heard of that on these before. And the timing would have to have been a complete coincidence, which is unlikely.+

 

I do agree that Iridium is not ideal for your car, but shouldn't cause any problems.

To access the plugs I removed only the washer reservoir, battery, and airbox. The throttle cable was not in the way, it started below the spark plug wires and I just kept it there. The throttle cable has slack to it.

The only code that is throwing is for the knock sensor P0327. The previous owner had work done on it and the mechanic instead of replacing the wire harness for the knock sensor, decided just to crimp them together with some electrical tape over the connection... Just another thing to fix, I have the parts just time needed.

Odd thing was that when I cleared the codes with the sensor, the car has a split second when it idles like normal. Doesn't seem like it is about to stall, it seems normal for about two seconds, the code kicks back in and then it starts to idle high again. I didn't think that code would cause the car to rev up like that though?

[Degree210]

3 hours ago, 1 Lucky Texan said:

no oil on the plug wire boots?

double check ground connections, if the knock sensor wire was broken, maybe other wiring was as well?

There was no oil on the plug wire boots. The knock sensor wire was already in bad shape when I got the car, it was only a matter of time. But from what I can see, there are no other severed connections. I will be having a second pair of eyes take a look at this with me the night after tomorrow to hopefully see anything I am missing.

[Degree210]

7 hours ago, heartless said:

basic copper core plugs are all that is required by that car (owners manual lists BKR5E-11 or BKR6E-11), you gain nothing by using the iridium plugs except a lighter wallet

gap is a little bit high.. spec is 0.039 - 0.043 - i usually set mine closer to the lower end.. typically about 0.040 - gap will slowly increase with age and wear...

the plug wires you purchased are the correct set for that car, just make sure they are fully seated at both ends.

and definitely check all the plumbing to the air box, and all vacuum lines..

Made sure the wires are fully seated, they are. Still problems persist. I was almost going to put the old plugs back in or change the gap on the new ones to see if that would help.

[Numbchux]

24 minutes ago, Degree210 said:

To access the plugs I removed only the washer reservoir, battery, and airbox. The throttle cable was not in the way, it started below the spark plug wires and I just kept it there. The throttle cable has slack to it.

The only code that is throwing is for the knock sensor P0327. The previous owner had work done on it and the mechanic instead of replacing the wire harness for the knock sensor, decided just to crimp them together with some electrical tape over the connection... Just another thing to fix, I have the parts just time needed.

Odd thing was that when I cleared the codes with the sensor, the car has a split second when it idles like normal. Doesn't seem like it is about to stall, it seems normal for about two seconds, the code kicks back in and then it starts to idle high again. I didn't think that code would cause the car to rev up like that though?

Sure doesn't make sense that the knock sensor code would effect the idle. But, it'll cause it's own issues. Might as well fix that issue first. Inspect the coolant temp sensor wiring while you're poking around.