Seems like the purge valve and canister are probably shot regardless of whether it is causing the idle problem simply because it is evidently open, leaking fuel and charcoal sludge, creating a rich fuel mixture, and causing a gurgling in the tank.

When you remove the purge valve and plug the opening in the throttle body, the idle problem persists. That could be due to a bad catalytic converter, or the sludge could be jamming up the throttle body as well - that could cause idle issues too. I can’t remember if you cleaned out the throttle body/intake manifold since discovering the sludge.

You might also need to reset the fuel adaptations (or let it run long enough without the purge connected) to get the car to adjust the fuel mixtures.

I wonder if you remove the purge line (and plug the throttle body and purge line so it acts like a properly closed purge valve), reset fuel adaptations, then check your pre- and post-cat o2 sensors, if things would look normal - pre-cat sensors gradually increasing and decreasing in a wave, and post-cat sensors more steady with a voltage somewhere around 0.4-0.7v or so. That might give you an idea how bad the cats are behaving.

Do you hear that rattling only when driving, or will it do it when revving the engine in park/neutral? If that rattling is the cats, then I would expect you’d hear it regardless. If you’re only hearing it in gear, then maybe this is another issue. If you are hearing it when in park/neutral, probably the cats - you can also tap gently with a mallet to see if you hear anything.

One thing though - if you’re still getting fuel and sludge through the purge valve, I would not be driving it with that purge connected. The charcoal might be abrasive to the cylinders, etc. if its getting that far. Might check the throttle body/intake manifold to see if its in there as well, and clean it out.

Still a major mystery as to why there are no codes.

This reply is a bit rambling - sorry. If I were going to tackle this myself, I think this would be my plan of action:

1. Try to determine if the rattle is coming from the cats or not. If not - if you have a transmission or drivetrain issue - maybe you’ve decided not to go further.
2. Clean out throttle body and intake manifold if necessary, and maybe change the oil;
3. Disconnect purge valve, and plug both throttle body connection and purge line opening to mimic closed purge valve;
3. Reset fuel adaptations;
4. Warm up engine and check post and pre cat o2 sensors (and the mid-cat sensors if you can access those values);
5. Depending on what is found from above, maybe get an emission test and, if it fails, seek to have the cats replaced under the emissions warranty.

 

No likely the cats, the rattle is ONLY under hard acceleration and NOT every time. It did it multiple times yesterday but did not do it today. Its a brief sharp noise like screws in a GLASS jar.

To clear up a misunderstanding, the purge inlet on the throttle body only has brown powdery soot, nothing wet. The full load breather on the intake is spotless. It is the part load breather on the throttle body connected to the PCV that is dripping dark molasses like fluid. I've had the throttle body apart and super charger apart multiple times for cleaning but nothing looks out of the ordinary.

I've reset fuel adaptations several times which seems to improve idle issues for a short while.

When I disconnected the purge valve, the rough idle did NOT go away, only the filler neck noises went away.

My software indicates 6 O2 sensors, 3 for each bank. Sensor 1 is indicated as wideband, today sensor 2 varied from .1 volts to .945 volts and sensor 3 stayed at around .7 volts. This was true for both bank 1 and 2. Earlier this month sensors 3 were reading 1.29 volts. However at the time of today's reading, RPM was staying at around 700 and was not dropping.

 

Also any idea what this part is? I noticed it sitting there after the main dealer replaced the radiator 6 months ago. Has a hose attachment on it which is not connected to anything. I removed the end cap and there is a white shiny foam membrane sealed at the end under the cap.

 

I believe that part you reference is the breather for the front diff. Mine is tucked in closer to the radiator.

A bad converter, when it’s making noise, sounds kind of like marbles to me - I’ve heard others say it sounds like glass. So I thought your description of screws in glass jar wasn’t too far off. But, obviously, I can’t hear it - you can. I take it from your post that it does not occur in park/neutral, or only in gear. So, I guess you’ve got something else going on.

The post-cat sensor at 0.7v certainly seems correct, so maybe the cats are okay.

I realize that disconnecting the purge valve didn’t fix the idle, but that doesn’t mean the purge valve is not shot - it pretty clearly is not functioning properly if it’s causing a gurgling sound in your tank at idle.

I misunderstood about the soot in the purge - thought it was wet. Either way, seems like that soot must be charcoal, and I expect the soot got into the valve from the charcoal canister being saturated. I can’t think of any other way that brown soot would get into the purge valve.

As for resetting adaptations, did you reset adaptations with the purge valve disconnected and the purge inlet and purge tube sealed shut? If you reset adaptations with a bad purge valve still pulling fumes from the tank, it’s just going to revert back to whatever fuel adaptations it had before.

As for oil in the breather, some oil from the part load breather is normal - not sure why it looks like molasses (dark-yes, but thick?) but they all drip a little oil. I know you changed the oil a while back and noted some swirls and an odd color as I recall, along with the odor of gas. You could get it tested, or drop the pan and see what else might be in there - might give you some kind of clue as to why that oil is so thick at the PCV.

Kind of running out of ideas on the idle issue. Seems like it’s got to be either ignition related or fuel control related. I believe you said you ruled out ignition. Fuel control has only so many parts: MAF sensors (2), coolant temp sensors (2), MAP sensor (throttle body), MAPT sensor (back of the inlet manifold, drivers side), o2 sensors, low pressure fuel pump, high pressure fuel pump, fuel rail pressure sensor, fuel injectors, throttle/position sensor, vacuum leaks/PCV, and the purge/EVAP system. Seems like you’ve ruled out a bunch of these as well, but maybe need to revisit. I’m happy to run comparative values for you off my car on any of these if you think it would be useful.

 

No, this was the first time I disconnected the purge valve so no I did not perform an additional adaptation reset.

Perhaps answer this about yours, does your idle behavior mirror mine? Does it usually sit at 630 but occasionally steadily stay at 700, 800, 900, 1100, 1200 regardless of whether AC, fans, heat, etc are on or off? Does it ever drop below 600 such as 500 or 550 rpm? If it does drop down that low, is that due to turning on various high load features such as heated windscreen, AC, etc?

I am confident the rattle is not the cats and is either drive line related or engine related.

Oil is off for analysis so waiting on that.

Part of the puzzlement is the shuddering/low idle is consistently inconsistent meaning it does not happen every time I drive but when it does happen, daily, it can be replicated until it can't be replicated. My daily driving routine is, well, routine and consistent so I can pretty much when and where it will happen.

 

No, my car idles around 630 (not sure on the exact number). The idle doesn’t move around, at least not that I’ve noticed. The only time it idles higher is on a cold start - it will idle high for maybe 20 seconds, which is normal. I have not noticed any difference in idle regardless of what kind of features are running. I’ll try to pay more attention to that, but I haven’t noticed any change.

You say the idle issue can be replicated until it can’t. What do you mean replicated? Is this when you remove the gas cap to induce the idle surging? Or is there something else that you can do to replicate it?

 

Yes, 630 seems to be the "happy" spot too. And of course closed loop cold start is ALWAYS going to have high idle.

The idle surging when opening the gas cap is more of a reverse surge. Idle at 630 and then every 5 seconds a drop and shudder to 500 rpm, then back to 630, back and forth (630 to 500 to 630 to 500) every 5 seconds for about 10-20 minutes.

As for the daily consistency, as an example. Normal cold start morning, 3 mile drive, sit in idle for about 5 minutes with idle at 630 and then it drops below 600 for a few minutes with shuddering, then back to 630. An hour later another short drive but this time idle sits constantly anywhere from 700-900 rpm. A few more short trips with varying idle speeds. in the afternoon another 3 mile or so drive with a 15-20 minute idle but this time idle sits consistently at 1100-1200 RPM. Turning on various accessories sometimes makes idle drop to 500 with shudder and sometimes it makes it jump from 630 to 700 with no shudder. Turning off accessories sometimes does the same thing, rpm drop or rpm rise.

Thanks again for your input.

EDIT: Cold start idle is about 1900 rpm and idle after cold start today was 900 rpm.

After all of these hardware tests could it in the end be a software issue with the ECU?

Also for the last couple of days I have been smelling a strong burning smell from the side and top of the engine compartment like burning rubber and tar. This is new because when I had numerous coolant leaks, the constant sweet smell of coolant persisted until the leaks were fixed and no smell but the normal hot engine smell for months.

 

Could be the ECU. I have been thinking about that possibility mainly because you are not seeing any codes at all. I recall seeing a post one time - totally different problem - but there were no codes being thrown when there should have been. This person had the PCM reset and it fixed whatever problem was occurring.

You also mentioned that the purge valve continues to click even when the car is idling even after you removed it from the throttle body. That means it must be getting an electrical signal to activate rather than simply chattering from the vacuum of the engine. You could check with a voltmeter. I’m not 100% certain, but I don’t think the purge valve should be activating when the car is just sitting at idle. Mine doesn’t seem to. If that’s true, it might also point to some ECU problem. I don’t have the specs on when that purge valve should open, but maybe you can find it.

But resetting an ECU scares the hell out of me.

Couple other things you could check: The throttle position sensors - when the car is running normally, take readings at different RPMs - make sure they’re consistent. Then, when the car is idling high, check the TPS readings against the readings when the car was running normally. If they are different for a given RPM level, then it might point to a faulty TPS sensor.

Fuel tank pressure: since you identified low idle issues when removing the gas cap, I’m wondering if your high idle issues have anything to do with pressure/vacuum building in the tank. Your recount of the symptoms seems to show that the idle gets faster as the day goes on. The engine is maybe staying a little warmer, but the fuel tank pressure also might be changing as the day warms up, car sits in the sun, etc. (This is really kind of grasping at straws).

Burning rubber smell - beyond belts slipping or the AC compressor going out, no idea really. You mentioned what you think are drivetrain noises - not sure if that could be related. I assume you checked brakes/tires for any rubbing.

 

WELL!!!!

After over 2 years this afternoon finally had a much needed MIL indicator!!!

DTC is Fuel Rail Pressure Sensor 1 FAILURE

 

An odd thing to be celebrating an MIL light, but some guidance at long last! What is the actual code number?