P0305 Code (misfire code) Topic is solved

[songzunhuang]

Sigh, today I changed out the camshaft sensor since my connector was in bad shape. This did not fix my misfire. While poking around in there, I noticed a hose that was in bad shape and had a crack in it. So I bought 4 feet of hose and replaced two hoses that were of the same vintage. Well, still misfiring.

I also routed all wires to make sure they are nowhere near the plug wires. I zip-tied various items to make sure they stayed in place. Still misfiring. It looks like a visit to the dealer is in my future.

Old sensor and new sensor. Replaced since old connector was in bad shape.

Sensors.png (683.54 KiB) Viewed 1998 times

[beigg]

you changed the rotor when you did the cap and wires?

[songzunhuang]

you changed the rotor when you did the cap and wires?

Yes I did.
This misfire has really got me stumped.

[beigg]

Disconnecting the injector harness plug connector and the spark plug wire from #5, does that change it any?

[sleddriver]

.....Well, it didn't fix the problem of the rough idling.

So to review, you're having a problem with rough idling and misfire codes being set while also at idle? Yet there's no issues when driving above a certain speed or on the freeway?

At idle, the engine management controller is in closed loop mode. Idle speed is controlled by the ISAC motor. Any unmetered air entering the system downstream of the AMM will cause problems & rough idling as the EMC won't know about the leak. When the idle speed stumbles, the EMC will try and correct for it, making it even worse. It may even oscillate...back & forth as it tries to correct for a mistake based upon a mistake......

Once you step on the gas, the EMC goes into open loop mode. Idle speed isn't an issue and the EMC reads the two O2 sensors for feedback.

Have you smoked the intake? Have you checked each of those two large, grey check valves we discussed in a previous thread? Since you've replaced a lot of ignition parts, perhaps the problem lies elsewhere, as in a vacuum leak. I built a simple smoke tester from a metal gallon paint can, old aquarium pump, some small dia tubing and used firework punks as a smoke source. You can also use incense. I used a big blob of electricians putty to weight the can & hold the incense sticks. Put the air intake hose down low on the side of the can and the output hose in the lid. This way the airflow will be bottom to top and your incense will have a steady supply of fresh air from below (like a BBQ grill). You could put two holes in the top, but the input hose needs to go to the bottom.

Also beware that those little vacuum caps on the ends of the vacuum tree will turn rock-hard over time. When they do, they won't seal. I used short pieces of silicone tubing closed off. Or you can connect two branches together. Also the main tree can leak down at the bottom where it meets the IM. I used anerobic sealant here + a new o-ring. (Belt & suspenders approach). Any other non-hardening sealant is fine. I found all of these leaks + more with smoke. Great time & frustration saver!

[songzunhuang]

.....Well, it didn't fix the problem of the rough idling.

So to review, you're having a problem with rough idling and misfire codes being set while also at idle? Yet there's no issues when driving above a certain speed or on the freeway?

At idle, the engine management controller is in closed loop mode. Idle speed is controlled by the ISAC motor. Any unmetered air entering the system downstream of the AMM will cause problems & rough idling as the EMC won't know about the leak. When the idle speed stumbles, the EMC will try and correct for it, making it even worse. It may even oscillate...back & forth as it tries to correct for a mistake based upon a mistake......

Once you step on the gas, the EMC goes into open loop mode. Idle speed isn't an issue and the EMC reads the two O2 sensors for feedback.

Have you smoked the intake? Have you checked each of those two large, grey check valves we discussed in a previous thread? Since you've replaced a lot of ignition parts, perhaps the problem lies elsewhere, as in a vacuum leak. I built a simple smoke tester from a metal gallon paint can, old aquarium pump, some small dia tubing and used firework punks as a smoke source. You can also use incense. I used a big blob of electricians putty to weight the can & hold the incense sticks. Put the air intake hose down low on the side of the can and the output hose in the lid. This way the airflow will be bottom to top and your incense will have a steady supply of fresh air from below (like a BBQ grill). You could put two holes in the top, but the input hose needs to go to the bottom.

Also beware that those little vacuum caps on the ends of the vacuum tree will turn rock-hard over time. When they do, they won't seal. I used short pieces of silicone tubing closed off. Or you can connect two branches together. Also the main tree can leak down at the bottom where it meets the IM. I used anerobic sealant here + a new o-ring. (Belt & suspenders approach). Any other non-hardening sealant is fine. I found all of these leaks + more with smoke. Great time & frustration saver!

Thank you for the detail. I've done a vacuum check as best I could without a smoker. I did change out a few vacuum hoses this weekend, but they don't appear to be related to the idle circuit as you described.

At this point, my lack of time to devote to this is dictating that I take it to a repair shop. I guess this is one of the downsides of having several old cars. They all take time to maintain! Also, my daughter is using this car daily so this behavior (the misfire at idle) is making her nervous.

[songzunhuang]

So I dropped the car off at a Volvo Specialist today and they did a leak down test.
Good news, #5 only lost 5% in the test. Definitely not a burnt valve. Whew!

They connected to an engine computer and noticed that my fuel trim was very unstable at idle. They suspected a vacuum leak. After some poking, they noticed that the gasket between the intake manifold and head on the lower left edge of #5 was crumpled a bit. You cannot see this gasket from above and it was unaffected by the torque of the bolt. When they sprayed some solution in the area, the idle would change. This is the prime suspect.

The shop is replacing the intake manifold gasket to see if this fixes the issue.
I will report back when they are done. I hope it's the issue. It's a cheap gasket, but it is 2.5 hours labor. Estimate is $300.

[erikv11]

Well at least we suggested how to find this problem, even if it didn't work out that way ... hope you got it fixed!

[songzunhuang]

Well at least we suggested how to find this problem, even if it didn't work out that way ... hope you got it fixed!

Well the verdict is in. The intake manifold gasket failed on #5 and was on it's way to failing on #1. This is disturbing as there was nothing wrong with the bolt torque. A stupid $15 part caused all this issue. I changed the gasket when I changed the PCV system back in August of last year. So the intake manifold gasket only lasted 9 months. Even more alarming is that I got the parts for this from IPDUSA, which normally only sells excellent stuff. Hmmm...

While they were at it, I got the shop to track down my P0455 error as well. Total bill. $477.83

So closes this saga. I threw over $300 of parts at this and it was all unnecessary.
I guess the stuff needed an update anyway. That's what I'm telling myself.

At least it wasn't a valve job. That was quoted at $1800-2000, but thankfully I didn't have to go there.
Thanks to everyone for this most educational experience.

[abscate]

Robert gets the Spinner Cup for this one....

3. Double and triple check for intake manifold leak

I should have advised you to use spray to test for idle fluctuation, well done by the dealer. They earned their money on this one