Lexus IS Forum banner

1 - 17 of 17 Posts

·
Registered
Joined
·
6 Posts
Discussion Starter #1
Heading to work the other morning I felt the car start running a little rough. At first I thought it might have just been a hiccup, after all it was cold and the car's got ~250k on the clock. Paid closer attention and felt it definitely missing, so I turned around and limped back home. The car was misfiring worse and worse, was barely running by the time I rolled into the garage.
Pulled the trouble codes and aside from two emissions leaks that had been there for... well... as long as I can remember... there were codes P0300 (random misfire) P0301 (cyl 1 misfire) and P0305 (cyl 5 misfire)
Great, simple enough... Went and bought a set of Denso iridium plugs and the premium spark plug wire set from O'Reilly that came with the 3 coil boots as well.
Got everything swapped out and back together (fixing a few vacuum leaks I noticed along the way) and fired the car up, it was still misfiring bad and would barely stay running.
Let the car sit overnight to deal with in the morning, when I started it again it was running a little bit smoother (still rough though), I was hopeful that it may just be oil that had emptied into the cylinders during the spark plug change that I hadn't been able to vacuum out.
The car continued to misfire, and trouble codes P0300, P0301, and P0305 returned quickly. After double checking all connections under the hood again (found one vacuum hose that wasn't connected, corrected that) and letting it run a bit more, P0303 decided to join the party. So now it's definitely misfiring on 1, 3, and 5.

I don't think it would be coils, since 2, 4, and 6 would also be throwing codes as well, correct?

There was an oily residue that appeared to have collected in the intake duct, almost looked and felt like Lucas oil stabilizer. I suppose it could be the MAF sensor if it got dirty, but wouldn't that throw it's own code and why would cyl's 1,3, and 5 specifically be affected?

What should I be looking towards next to troubleshoot this problem?

Thanks in advance...

PS. Car is stock except for a high flow air filter in the factory air box
 

·
Registered
Joined
·
2,389 Posts
Check the coil connectors and the one on the ignitor. If the valve cover are leaking. The oil will cause this also. It could be coils. But with so many and all of a sudden doing it. I doubt it.
 

·
Registered
Joined
·
6 Posts
Discussion Starter #3
Thanks for the reply!

Coil connections all snapped firmly into place when I put everything back together, I will double check though to be sure.
I picked up a can of MAF cleaner, removed it and cleaned it, cleaned the intake duct really good, and threw in a bit of Seafoam into the gas tank. The car seemed to be running smooth enough to drive up the street to the gas station where I topped it off. At higher RPM's (~3k+) the engine feels smooth, though does seem to lack power. By the time I returned home the car wasn't running worse or anything, but there was the smell of what I could only describe as heat. Not the engine overheating, not anything on fire, but something was definitely getting hotter than usual. There was a bit of smoke coming from the back of the engine and it didn't smell like oil. Could a clogged cat be the culprit?
Ordered an infrared thermometer which should arrive tomorrow, my brother (is300 owner as well as all around gearhead) said testing the temp before and after the cats should provide pretty solid confirmation of this or rule it out. Am I on the right track here?

Igniter was never unplugged, and it does appear to be a clean and solid connection.

Let me double check all electrical connections at the coil packs and see what happens...
 

·
Registered
Joined
·
2,389 Posts
Thanks for the reply!

Coil connections all snapped firmly into place when I put everything back together, I will double check though to be sure.
I picked up a can of MAF cleaner, removed it and cleaned it, cleaned the intake duct really good, and threw in a bit of Seafoam into the gas tank. The car seemed to be running smooth enough to drive up the street to the gas station where I topped it off. At higher RPM's (~3k+) the engine feels smooth, though does seem to lack power. By the time I returned home the car wasn't running worse or anything, but there was the smell of what I could only describe as heat. Not the engine overheating, not anything on fire, but something was definitely getting hotter than usual. There was a bit of smoke coming from the back of the engine and it didn't smell like oil. Could a clogged cat be the culprit?
Ordered an infrared thermometer which should arrive tomorrow, my brother (is300 owner as well as all around gearhead) said testing the temp before and after the cats should provide pretty solid confirmation of this or rule it out. Am I on the right track here?

Igniter was never unplugged, and it does appear to be a clean and solid connection.

Let me double check all electrical connections at the coil packs and see what happens...
Yes it could be a cat. If it is smooth until it warms ll the way up.
 

·
Registered
Joined
·
6 Posts
Discussion Starter #5
Connections appear good, temps before/after cat(s) don't indicate anything wrong with that system, cleared the memory and ran with the MAF unplugged then plugged in and while it didn't make much of a difference, I don't think that's the culprit because if it was, all cylinders would be misfiring.
The only thing I can think of is that the misfires are coming from the cylinders that have a spark plug wire connecting them to the coil, the cylinders with the coil directly on the plugs are fine. The wires are new and the misfire existed before changing them, so I don't think it's bad wires... Is there any reason why the plugs connected by wire wouldn't be getting enough power while the ones directly connected to the coil do?
 

·
Registered
Joined
·
2,389 Posts
Connections appear good, temps before/after cat(s) don't indicate anything wrong with that system, cleared the memory and ran with the MAF unplugged then plugged in and while it didn't make much of a difference, I don't think that's the culprit because if it was, all cylinders would be misfiring.
The only thing I can think of is that the misfires are coming from the cylinders that have a spark plug wire connecting them to the coil, the cylinders with the coil directly on the plugs are fine. The wires are new and the misfire existed before changing them, so I don't think it's bad wires... Is there any reason why the plugs connected by wire wouldn't be getting enough power while the ones directly connected to the coil do?
Could even be bad coils. I have had one fail on the plug wire side only before.
 

·
Registered
Joined
·
237 Posts
I would also put my money on bad coils given everything you've described. Just days ago I switched my coils trying to diagnose a gear related problem. And when I went back to my newer replacements once I fixed my main issue, all was good again.

Just understand that auto parts stores, particularly dealers charge an arm and a leg for new coils. The generic ones made for our cars online, amazon has a few, the price comes in at a much more reasonable ~$20/coil. Beats paying $80-130/coil elsewhere. Those are the ones I've been using for nearly two years and haven't run into any quality issues, so take that for what it's worth.


At higher RPM's (~3k+) the engine feels smooth, though does seem to lack power.
Misfires on a few cylinders can be masked once the rotating assembly enough inertia to spin more freely. But you know it's down on power, so it's likely a spark related issue.

Great, simple enough... Went and bought a set of Denso iridium plugs and the premium spark plug wire set from O'Reilly that came with the 3 coil boots as well.
Did you check the gap before installation? OEM gap is 0.041" or 1.1mm for stock N/A configurations
 

·
Registered
Joined
·
6 Posts
Discussion Starter #8
I would also put my money on bad coils given everything you've described. Just days ago I switched my coils trying to diagnose a gear related problem. And when I went back to my newer replacements once I fixed my main issue, all was good again.

Just understand that auto parts stores, particularly dealers charge an arm and a leg for new coils. The generic ones made for our cars online, amazon has a few, the price comes in at a much more reasonable ~$20/coil. Beats paying $80-130/coil elsewhere. Those are the ones I've been using for nearly two years and haven't run into any quality issues, so take that for what it's worth.




Misfires on a few cylinders can be masked once the rotating assembly enough inertia to spin more freely. But you know it's down on power, so it's likely a spark related issue.



Did you check the gap before installation? OEM gap is 0.041" or 1.1mm for stock N/A configurations
The parts store by my house only had one of the coils in stock, so I bought it figuring if I can confirm that it's the cause I'll drive across town to the other store to pick up the other two. I thought about buying the generic ones online since they are significantly less expensive, but at this point honestly time is money and I don't want to wind up with fitment or warranty issues over a relatively small amount of money.
So... Brought the coil home, took off the throttle body and since the rear coil was the easiest to access (cyl 6 with the wire going to cyl 1, which is one of the misfires) I replaced it first. Hooked everything back up, fired it up, and let it run for a few minutes while doing some much needed tidying up in the garage. It idles alright, but with a little bit of throttle it's still clearly misfiring but the check engine light wasn't on. Took it for a ride around the block and the light flashed, but at idle seemed to remain off.
Checked the codes and it's still the same P0300, P0301, P0303, and P0305. Nothing's changed there.

I'm tempted to go buy the other two coils and just triple check all electrical connections while everything's apart, but don't want to waste $160 on the two coils if the current ones are functioning properly.

As for the spark plug gap, I was under the impression that iridium plugs came pre-gapped?
I might take them out just to see what they look like...
 

·
Registered
Joined
·
2,389 Posts
The parts store by my house only had one of the coils in stock, so I bought it figuring if I can confirm that it's the cause I'll drive across town to the other store to pick up the other two. I thought about buying the generic ones online since they are significantly less expensive, but at this point honestly time is money and I don't want to wind up with fitment or warranty issues over a relatively small amount of money.
So... Brought the coil home, took off the throttle body and since the rear coil was the easiest to access (cyl 6 with the wire going to cyl 1, which is one of the misfires) I replaced it first. Hooked everything back up, fired it up, and let it run for a few minutes while doing some much needed tidying up in the garage. It idles alright, but with a little bit of throttle it's still clearly misfiring but the check engine light wasn't on. Took it for a ride around the block and the light flashed, but at idle seemed to remain off.
Checked the codes and it's still the same P0300, P0301, P0303, and P0305. Nothing's changed there.

I'm tempted to go buy the other two coils and just triple check all electrical connections while everything's apart, but don't want to waste $160 on the two coils if the current ones are functioning properly.

As for the spark plug gap, I was under the impression that iridium plugs came pre-gapped?
I might take them out just to see what they look like...
If there was no change in that cylinder with new coil and all. I am thinking to look at the ignitor being bad. There is a small possibility of the TPS also.
 

·
Registered
Joined
·
237 Posts
The parts store by my house only had one of the coils in stock, so I bought it figuring if I can confirm that it's the cause I'll drive across town to the other store to pick up the other two. I thought about buying the generic ones online since they are significantly less expensive, but at this point honestly time is money and I don't want to wind up with fitment or warranty issues over a relatively small amount of money.
I understand, I was in a simliar boat just a few days ago with getting a new VVT-i sprocket. Either immediately get a new one from the dealer for $340, or wait a couple days and buy a Viton O-ring for $5. I needed to know what the issue was fast, so bye bye monies.

I'm tempted to go buy the other two coils and just triple check all electrical connections while everything's apart, but don't want to waste $160 on the two coils if the current ones are functioning properly.
You can always flip the one you bought around in hopes that two of your others are actually working ok while you wait for the generic ones. Amazon has the 3 pack on prime if you're a member, take advantage of that sweet sweet one day shipping haha

As for the spark plug gap, I was under the impression that iridium plugs came pre-gapped?
I might take them out just to see what they look like...
I remember having to gap my OEM Denso plugs, took a minute to get them all to spec, but once they were I didn't have any issues.
 

·
Registered
Joined
·
643 Posts
As for the spark plug gap, I was under the impression that iridium plugs came pre-gapped?
I might take them out just to see what they look like...
I changed my plugs at the 100,000km recommended swap about 5 years ago, i hadnt had the car long and it turned out someone had put the copper ones in, so i put the OEM denso iridium back in. Just changed the timing belt the other week at 160k km and while i had it all apart i thought i would check the plug gaps, i havent had it apart to check them since i put them in. All were between 1.1 - 1.3mm so i regapped them back to the factory spec, but i thought that wasnt to bad all things considered, though i dont thrash it much and it never gets raced.
 

·
Registered
Joined
·
321 Posts
I’d hold off shooting the parts cannon at it just yet.

1) Any chance moisture got down there? If so water can and will boil and pop off the plug wire when it warms up.

2) Are you sure nothing happened with the fuel injectors?

3) I’d pull 1 wire off at a time and put on an old spark plug. Start it and leave it sitting on the block to ground it and you should be able to verify if the coils are firing.
 

·
Registered
Joined
·
6 Posts
Discussion Starter #13
If there was no change in that cylinder with new coil and all. I am thinking to look at the ignitor being bad. There is a small possibility of the TPS also.
Hmm... Is there any way to test the ignitor? My brother has an IS as well and has offered to send it to me in the mail since his car is parked for the winter (haha, sucks to live where it snows!) to try out.
As for the TPS, wouldn't that trigger its own code as well? And how come only 1-3-5 would be affected and not 2-4-6?

I remember having to gap my OEM Denso plugs, took a minute to get them all to spec, but once they were I didn't have any issues.
I changed my plugs at the 100,000km recommended swap about 5 years ago, i hadnt had the car long and it turned out someone had put the copper ones in, so i put the OEM denso iridium back in. Just changed the timing belt the other week at 160k km and while i had it all apart i thought i would check the plug gaps, i havent had it apart to check them since i put them in. All were between 1.1 - 1.3mm so i regapped them back to the factory spec, but i thought that wasnt to bad all things considered, though i dont thrash it much and it never gets raced.
I will take the plugs out and check the gap, I'm skeptical that this is the cause of the problem however since these were the codes that were in the computer before I changed the plugs as well.

I'm going to hold off on buying the other coils for now since the misfire in cylinder 1 didn't go away with the first new coil.
I guess for now I'm going to wait for the loaner ignitor and see what that does, unless any new ideas come up. I'll be sure to post an update if anything new happens. Thanks to all for the ideas and suggestions!
 

·
Registered
Joined
·
2,389 Posts
I do not recall a test procedure on the ignitor. You could do a bit of reading in the factory service manual. Other than that. If you can barrow one. That would work very easy except for shipping time and cost.

The TPS usually would make other codes pop. But unless we see some other things. We are drawing at straws. If the plugs were wet with gas. I would say leaking injectors.
 

·
Registered
Joined
·
237 Posts
I will take the plugs out and check the gap, I'm skeptical that this is the cause of the problem however since these were the codes that were in the computer before I changed the plugs as well.
I've come to learn our ex's can be touchy when it comes to misfires, sometimes picking them up when there seemingly isn't an issue.

A regapping would be ideal as it's the cheapest way out haha
 

·
Registered
Joined
·
6 Posts
Discussion Starter #16
Okay, so here's the latest.
My brother mailed me the ignitor from his IS300 and it made no difference, so it's probably safe to rule that out.
While on the phone troubleshooting a few other possibilities with him he suggested clearing the memory (unplugging the battery) and then disconnecting the TPS to see what would happen.
Interestingly the misfire went away and it idles nice and smooth. Now, with the throttle design on this car and the limp mode that I guess is enabled under these sorts of conditions, there is no pedal response until ~80% throttle and even then it responds differently than when the TPS is connected and functioning properly, but a quick spin around the block and the misfire seems to go away. After getting back to the garage, I pulled the codes and there was only one code: P1120. No misfire codes. Great!

So off I go to the O'Reilly Auto down the street to pick up a new TPS sensor for a whopping $91, get back, and realized that what I had unplugged (and had appeared to take care of the problem) wasn't in fact the TPS sensor. I had unplugged the connector on the back side of the throttle body near the accelerator cable, and saw that the TPS (based on the one I got from the store) was on the front of the throttle body. Ugh!

From what I have been able to find, I had unplugged the "Accelerator Pedal Position Sensor", and of course there doesn't seem to be an aftermarket replacement available from the local parts stores. I found one on PartsGeek for $130 which is awesome, my brother is mailing me his throttle body to try before buying, so we'll see if this ends up solving the problem.
 

·
Registered
Joined
·
2,389 Posts
Okay, so here's the latest.
My brother mailed me the ignitor from his IS300 and it made no difference, so it's probably safe to rule that out.
While on the phone troubleshooting a few other possibilities with him he suggested clearing the memory (unplugging the battery) and then disconnecting the TPS to see what would happen.
Interestingly the misfire went away and it idles nice and smooth. Now, with the throttle design on this car and the limp mode that I guess is enabled under these sorts of conditions, there is no pedal response until ~80% throttle and even then it responds differently than when the TPS is connected and functioning properly, but a quick spin around the block and the misfire seems to go away. After getting back to the garage, I pulled the codes and there was only one code: P1120. No misfire codes. Great!

So off I go to the O'Reilly Auto down the street to pick up a new TPS sensor for a whopping $91, get back, and realized that what I had unplugged (and had appeared to take care of the problem) wasn't in fact the TPS sensor. I had unplugged the connector on the back side of the throttle body near the accelerator cable, and saw that the TPS (based on the one I got from the store) was on the front of the throttle body. Ugh!

From what I have been able to find, I had unplugged the "Accelerator Pedal Position Sensor", and of course there doesn't seem to be an aftermarket replacement available from the local parts stores. I found one on PartsGeek for $130 which is awesome, my brother is mailing me his throttle body to try before buying, so we'll see if this ends up solving the problem.
Yeah, the app sensor is not cheap and I do not know any regular auto parts store that can get it. I would replace it and the TPS.
 
1 - 17 of 17 Posts
Top