Car doesn't want to idle

Need a second set of eyes on this - I am stumped and feel like I may be overlooking something. This is long, so I appreciate any help. Car has always driven really well, until one day I smelled fuel after parking it in the garage after a long day of driving through the mountains on a hot Summer day. The night prior, I had filled the gas tank up and was messing around and accidentally overfilled it. After a few days of troubleshooting, I came to the conclusion that I needed to replace the evap vapor canister in the passenger side wheel well. I ordered the OEM part and replaced, smell went away. I drove the car for 35 minutes after I replaced the canister and the car ran great, life was good. Drove it to take the kids to lunch the next day and the car died when coasting to a stop. It immediately started right back up and idled fine, had no problem getting lunch and getting home. I double checked to make sure I hadn't forgotten to tighten the battery cable, which I have had on and off a quite a few times while troubleshooting. I put the car in the air and double checked the evap pieces I had just replaced, double checking the lines weren't mixed up and smoke tested the system again to ensure no leaks, I found none. I put the car back together and the problem just keeps getting worse, to the point where it is difficult to start cold and doesn't want to idle. If I provide a little assist via the gas pedal, I can get the car up to temperature and then it was idling fine. Taking it for a test drive, it struggles from a dead stop (hesitates really bad) and feels like it struggles below 2k rpm as well. 3k and above the car runs great. Here is a list of things I have done: - Replaced the evap vapor canister - Checked the evap purge valve to make sure it isn't stuck open. It is closed and I can hear it actuate when applying 12v - Smoke tested intake manifolds and vacuum lines connected to them. I found the resonance flap actuator leaking on the rear crossover tube, which I have sealed up temporarily and it is no longer leaking. I also found the manifold adapter where the brake booster line hooks up leaking a bit, I have also temporarily sealed that until I can get a new part. Cannot find any more leaks, everything on the intake looks good. - I replaced the MAF with a new Bosche MAF. The problem did not change. - I have isolated the evap system from the engine completely to eliminate a leak in the evap system by removing the purge valve and capping both the end of the valve and the vacuum port on the throttle body. No change to the problem. Looking at my scan tool, the long term fuel trims are way out of whack. They are sitting at 32% on both banks until I go almost full throttle, then they drop to 0%. This is the first thing leading to me thinking I have a fuel delivery problem. The long term fuel trims do not change if I unplug the MAF and drive. I have twice now got the check engine light to illuminate, kicking out P1126 and P1133, my scan tool tells me P1133 is "Oxygen Sensing adaptation frau bank 2 lower load range". Tomorrow I am going to check fuel pressure at the rail. I am starting to think either the fuel pressure regulator is bad or the fuel pump is going out. The thing I am having a hard time wrapping my mind around is, if it is a fuel delivery problem, why does it run better under load at higher RPM? I am having a difficult time believing this is a coincidence and just so happened to start acting up the day after I replaced the Evap vapor canister. What am I missing?

Looking at the fuel tank and have a few questions. All the info I see online seems to be for a C2 which appears to have a slightly different setup. I only have the two plastic lines that hook up. Which one is the supply line and which one is the return line? Also, there is a nipple that has nothing connected to it, should there be? Lastly, there is this adhesive type stuff on one spot on the black sealing collar. Is this an OEM tamper proof type thing or has someone before me been messing around in here? I wonder if they applied the adhesive in an attempt to seal a crack or if there would have been another reason. It appears that it was applied and then the seal was broken intentionally.

Usually this is a big open leak on the intake side. But you smoke tested forever and it's OK. It's quite logical to look at the last thing you did with suspicion, but you leak tested it and there's no way it can lead to over-fueling. It kind of sounds like a progressively failing fuel pump. But with those codes I would first check your wiring to the pre-cat O2 sensors. The argument against the wiring or the sensor being bad is that it was running fine for quite some time. What does the scan tool show for O2 sensor voltages? Here are mine when my cats went bad. The pre signal is what to expect. I don't know what it would look like to create the over fueling you have. Good luck.

There are a few threads that talk about the issues with this connection into the fuel tank. Yes, they do crack. I recall the nipple with no connection is normal. I also recall that some of the tubing in the tank connecting these lines to the pump will sometimes split and leak internally. Certainly something to search out. Or maybe just haul it out of there and inspect it.

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Yeah, that�s on my list of things to checkout. Was going to crack into it tonight but wanted to understand the system a little better. I forgot to mention I tested the AOS with my manometer and it�s good, as well as smoke tested the oil fill tube and found no leaks.

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Thicker of the two will be return line. That adhesive is not from the factory. Like you, I suspect a repair attempt. I would remove it to see what is underneath.

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That�s the confusing part, they are exactly the same diameter.

If u unhook them one nipple is larger then the other. I suspect that the chsrcoal canister had nothing to do with your issues and its just manifesting into additonal issues. More needs to be done to find the root cause of the codes. Checking fuel pressure is a good start.

Your symptoms (fuel trim pulling fuel) and poor running at low rpm sound similiar to the issue I have been chasing too. Check fuel pressure at idle and while accelerating. Also check that it holds pressure when the engine is shut off. For a C2, spec is 54psi at idle. I cannot recall what the leak down spec is. Check your MAF. It should read 14-15 kg/hr at idle on a 3.6. Unrelated to the above low speed stalling, My fuel pump went out years ago and I replaced it. However I created another leak on the sender where the lines connect because the plastic gets brittle with age. Hairline cracks caused a small fuel leak that smelled of gas when I drove the car. Replaced the sender and all was good.

Just got finished checking the fuel pressure at the rail: 0 psi with the ignition switch on but the engine off. Thought this was odd but seems that the pump doesn�t prime until it seems a signal from the crank position sensor (from what AI tells me). 30 psi at idle but struggling down to 20 psi. Time to get into the tank I guess. Also, seems the C4S uses a �returnless� fuel system, there is no return line.

Yes all 996.2 cars has the pressure regulator and return inside the fuel tank its self ( ie. no return line from the engine) I have seen that glue on the fuel tank lid before and thought it was odd, but evidentially it is from the Factory, maybe just to keep the big nut from vibrating loose...IDK...lol There has been several instances of a rupture in the small rubber line inside the fuel tank causing a low pressure/low flow volume....may be a quick/easy/inexpensive fix

Simple diagnosic test.....hopefully leading to a simple fix.

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Yes, I watched a video of another changing their fuel pump out and saw the same adhesive mark on his. I�m going to carefully pull everything out and inspect as I go.l, I�ve read about that rubber line your referencing, definitely going to check that. Draining some fuel out before I open the tank. Took the gauge portion off my tester, hooked up some tubing, and jumped the fuel pump relay to pump some of the gas out.

Ok - removed the sending unit and peeked inside, everything seems hooked up correctly and it doesn�t look like anyone has been in here before. One wire from the sending unit to the pump has lost all its insulation in a few different spots. The plastic tubes look good but there is only one way to know if they have a crack and that�s by running the pump from what I can tell. Thinking of making a long harness to plug in to the connector and then running it to a 12v battery plenty far away, that way I keep any chance of a spark away from the open fuel tank. Is that a dumb idea or is there a better way to do it?

Sounds ok to me but I have done a LOT of dangerous **** in my life .....

Quotes source post: 20671229

Ha same! I did make some wires to connect to the externally located battery and removed the level sending unit, so I could see inside the tank while the pump was running. The pump would run but it was not actually pumping any fuel. I expected to see fuel coming out of the lines that would have connected to the sending unit but nothing happened. I reconnected the sending unit and ran some tubing from the top of the unit over to a 5 gallon bucket and reattempted. Was very difficult to see anything but it didn�t look or sound like anything was splashing around in the tank or �hissing� out of a cracked line, so that�s about as good of a look as I�m gonna get. Not sure at this point if it�s the pump or the fuel pressure regulator, but I�m not sure it matters. The FPR is mounted on the sending unit and it doesn�t look like I can buy it separately. I guess I�ll probably just ordered a new pump kit with the new sending unit so I don�t have to mess with this again. Not cheap, $1500, but it�ll at least be done.

Its just the pump. Save your $. Edit: i reread your test and as said below. Pull the entire thing out and inspect all the hoses first.

First thing, take the pump and the venturi pumps (two of them) out of the tank. Inspect the lines very carefully for cracks. I'll bet the U shaped tube is split. That can be replaced for like $20. Get a foot of *submersible* fuel line on amazon. Make absolutely sure it is submersible! Replace the U shaped line. Use fuel injection clamps. Put everything back together. I have done this repair between track sessions. It's super easy. BTW that glue has been on every VWAG car I have changed a fuel pump on. I'm sure it's a factory tamper seal.

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Yeah I guess that�s probably the best idea, just remove and fully inspect it. Are you taking about the hose that failed in this guys pictures? The black rubber hose?

Yes that black hose.

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Wow, would not have expected that! Large scale production normally don't like handling dribbly nor smeary stuff for risk of contamination down the line.

Pulled the fuel pump and Venturi tubes out today. Thought I was pretty careful when I removed the pump, found this tube sheared completely. My guess is that it was split and I finished it off when removing it. I inspected it prior to removal and couldn�t find any cracks (pics below) but it might have just been splitting and I just couldn�t see it. Or maybe it was just that brittle and broke completely with the slightest force. Inspected the Venturi tubes as well and they look good but I feel like it�s just a matter of time before one becomes a problem. The car is 23 years old. Because I�m building this car for driveability and road tripping, I ordered a new pump and new Venturi tubes. I could see those things just failing one day in the middle of nowhere and us being stranded, rather just have the piece of mind. Super easy job but not cheap.

Good on ya for doing the work and finding the problem! The split line is a tricky one as the gas doesn't end up on the ground. It shows as all kinds of odd drivability issues. On my car it gradually got worse. At first it ran ok at less than 1/2 throttle. Then it barely had enough power to go 45 mph. Finally I had to push it into the garage as it wouldn't run at all. BTW that corrugated hose is available as aftermarket parts from several sources.

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Yeah that seemed to be how my car was - just got worse over time. I thought about just doing the hose but then thought how I�d be kicking myself if the pump failed on me in the near future. I also put a lot of value in convenience at this point in my life because things are busy! I spent about 10 minutes pulling the parts out today, and 5 minutes making the decision to order new ones because Pelican had them in stock and I�ll have them in two days haha! Frees up the limited amount of brain bytes I have to focus on other stuff.

Well the new fuel pump is installed and all is well again. Thanks to all of you who commented and helped! This happening the day after I installed the evap vapor canister really threw me for a loop at first but turns out it was just coincidence. Glad to have it sorted! Fuel pressure at idle is now inline with the spec and the car drives great again! Just in time too, wanted to get this wrapped up and solved before this goodness showed up.l: