VW Eurovan '02, engine light on, sputters, feels like vapor lock when rainy

I have a 2002 VW Eurovan, 2.8L V6 Winnebago Vista 21B, 130k miles, my check engine light is on but having a hard time trying to figure out what’s causing it and what direction to head without spending a fortune. It started while traveling across country two years ago, several days into the trip, after driving several hours at freeway speeds on a cool rainy day, I stopped for gas and when I turned it back on it sputtered and coughed and ran REALLY rough, I slowly moved the vehicle out of the way, about 50 ft, turned it off and when I turned it back on it was fine, except the check engine light came on. I took it into VW and they ran the test… the codes were:
P0118 Coolant Temperature Sensor 1
3 Cylinder Misfires P0305, P0300, P0303
P1151 Bank 1, mixture adaptation, range 1, Lean limit not reached, static

They said it wasn’t going to destroy the vehicle, to continue on my trip and I’d need to do some sleuthing to find the culprit. The light came on and off throughout the trip but didn’t have the sputtering again ( although I didn’t push it as hard when driving it either, kept it around 65 - 70).
Got back to Montana and a local shop replaced the ignition coil.
That didn’t fix the check engine light, which is on continuously now (that’s been 2 years with mild use of about 8k miles). Until now, it hasn’t sputtered again so I didn’t really worry about it, but it happened in Oregon last week when it was again cool and rainy, I’d been driving hwy speeds for a few hours, I stopped for gas and when I restarted it sputtered, coughed and rumbled like it did 2 years ago. I turned it off for 30 secs, restarted and it was fine.
In talking this over with a variety of folk, we’re thinking the issue could be a fuel filter, fuel pump, coolant sensor or catalytic converter sensor… I have a fuel pressure test scheduled in a couple of weeks. Has anyone had this issue before? Thanks for your help and have a great day!

Let’s see, its not vapor lock and the computer will have no idea what the fuel pressure is or if the pump is on. So if you have a light on, the computer has set a trouble code that is to be used to lead to resolution of the problem. What makes you think it is not a bad coolant sensor which is used to set the fuel ratio?

After two years just get a computer diagnosis and let them track it from there.

A faulty engine coolant temp sensor code means either the sensor is bad, the wiring to it is faulty, or the thermostat isn’t properly regulating the coolant temp. It should be easy for a shop to test the calibration of the sensor and verify the sensor’s connectors aren’t corroded. It’s a rare thing coolant temp sensors go bad though. If it tests ok, next step is to replace the engine thermostat probably. You’ve got to focus and fix this engine coolant temp sensor code first, b/c it may be causing all the symptoms and fault codes.

Does the dashboard coolant temp gauge act like it should? i.e. it starts off low then moves to around the mid-point and holds there when the engine warms up after about 15 minutes of driving?

I expect you have more than one problem. After you address the coolant temp sensor code, if the “vapor lock” symptoms persist after filling the tank, another problem may be the fuel tank evap system. When you fill the tank w/gas various valves are supposed to switch on or off so that a big dose of gasoline vapors doesn’t get pushed into the engine as the tank fills. If one of those valves fails, it can cause a flooded condition when you try to start the engine just after filling the tank. Usually that condition throws a code but the engine coolant code and the misfire and mixture codes may be masking it for some reason.

I wouldn’t worry too much about the P1151 for the moment. I’d check and replace the coolant temp sensor if needed.

The rough running after rain could be due to aged spark plugs and/or possibly the plug wires. Replace the plugs and check each wire with an ohmmeter. I believe the wires on that particular model may have resistors in the ends so make sure all wires show roughly the same resistance. The old or new wires along with the ignition coil could be sprayed down with WD-40 as that can help prevent moisture induced arcing.

The rough running, turning it off, and running fine after a restart could be a fuel pressure loss problem; check valve in the pump, fuel pressure regulator, or an injector sticking open.

It sounds like the fuel pump is not retaining pressure after the engine is switched off. If this occurs when the engine is very hot the fuel in the fuel rail will boil and push the fuel in the line back to the tank, a form of vapor lock. Are you experiencing a long crank time when starting the engine?

Thanks for your insight George, the dashboard coolant temp acts normal; starts out cold and when it warms up it is dead center on the gauge, I think it reads 190, and I do check it regularly while I’m driving. I have never seen it overheat. The idea of a bad connection makes sense, especially when it gets wet, so that is what we’ll check next. I live in somewhat of a remote area and my favorite mechanics don’t work on Europeans, and the one they say is good doesn’t have a tall enough shop to get me in… so we may try checking the wiring on our own and then having the codes run again.
And Nevada, the crank time is normal as well.

Ok… Just got the Trick Winnie back from the local European auto shop… they couldn’t get my vehicle inside their building but they said they’d try to work on it anyway. They ran the codes (the third time now) and this time a code came up for the 16891 Idle Control System, 17559 Long Term Fuel Tirm, and several cylinder misfires… but no Coolant Sensor. Turns out it was a cracked Booster Vacuum Hose. Since it’s going into winter storage, we won’t truly know for awhile if this is it, but it sure sounds like the culprit. Those codes didn’t come up on the first two runs of the codes, and the wiring on the Coolant Sensor could still be a problem and just triggering that code randomly, I will try to check that… Thanks for all the input! I really appreciate you taking the time on my mystery.

The fuel trim error must have led them to some path allowing un-metered air into the engine. Good for you for getting it fixed. Brake power boosters are a common vacuum leak source. They’ll typically cause lean codes and misfires. A lot of times a vacuum leak like that will cause a sort of hissing noise too. That’s often what the owner observes. This could in theory anyway cause an overheating condition too. Maybe that’s the relationship to the coolant sensor code. Seem dubious, but at least now you’ve got a theory … lol …

The reason a vacuum leak can cause overheating is b/c excess air into the engine is sort of like blowing air on a fire. It heats up faster that way.

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