Engine behaving strangely and popping hoses off intake manifold

So a couple weeks ago during a trip I noticed the engine behaving strangely: reving up and down repeatedly, reving up while slowing down to a stop as if it was engine braking, and running constant once stopped, when it's not supposed to.

On the way home going uphill I heard a pop sound.

Going down hill using engine brake, I heard an unusual whoosh sound while engine braking.

After that, using the engine again, it was performing much worse, until `CHECK HYBRID SYSTEM` came on and forced me to pull over (near home). Error codes were P3190, P0171, P0101, P3190, P3190

After restarting it was able to continue but ran very badly and shut down again after stopping at the gate.

Turns out the PCV hose popped off the intake manifold, causing a massive intake leak. That's what the whoosh sound was from.



I had a look in the tube and at the time thought it had a lot of build up in it but didn't bother with it.



So I attached it securely with a worm-gear clamp and thought that was the issue fixed.



Last weekend, we did the same trip, and noticed the engine behaving strangely again! When I parked and the engine continued running, I had a look under the hood but heard no intake leak. There were no pending error codes.

Nothing happened until we got home, and nothing happened for most of a week while my father went to work with it, until yesterday; it failed again right when he entered the lot (and he creeped into the parking garage). So he took a rental and next day I went with him to fix it.

This time the EVAP hose popped off the pressure switch thing. Error codes were P3190, P3190, P3190, P3191



I put it back on; didn't have any clamps but was going to add a hose clamp at home.

It appeared that somehow the intake manifold was having a positive pressure, enough to blow hoses off. My hypothesis was that the engine brake caused a positive pressure in the intake manifold… and based on my assumption that the PCV hose had a lot of build up, the PCV valve must be clogged, and was not letting excess pressure through (I thought PCV valves let pressure both ways at the time). And we never cleaned or changed the PCV valve with 212k miles. So I thought we should get a new PCV valve, and also should clean the intake manifold which I thought would certainly be very dirty with that disgusting EGR piping into it.

After a while of city driving, during and after getting off a freeway, the strange behavior happened again, then POP (during acceleration from stop), followed by the smell of sulfur dioxide (smells like kitchen match burning). So I stopped at a parking lot and had a look with a camera; that hose popped off again! I was able to reach under the air box and plug it back in without disassembling stuff again.

This invalidated my hypothesis that it was the engine brake, as little or no engine braking was used. (It could have done it a little during regen but the battery wasn't full so I don't think it did)

When going home (which involves going over a hill) I tested how the hose might be popping off: I powered hard up hill and then used engine brake excessively going down hill. Looked (felt) the hose; IT DIDN'T MOVE A BIT!

I took out the intake manifold (which was surprisingly quick and simple) to clean it and replace the PCV.

I realized that what I thought was build-up in the tube was actually the shape of the tube itself!!

(also at some point before I realized that the PCV valve only lets flow in one direction so it wouldn't backflow anyway; or at least I couldn't blow in the opposite direction… I do not know, does it let though with enough pressure?)

The PCV valve… was perfectly fine. It had no build up, just some discoloration; and it sounded just like the new one when shaking it. (and pressing the spring felt fine too) so I cleaned it with the carb cleaner (wasn't much to clean) and put it back; left the new one to return. What's with people cleaning or changing their PCV valves after ~30k miles?! When ours has 212k and is still perfectly clean! I do not know, maybe it has less than that, but I'm pretty sure it has a lot more than 30k...

Cleaned the intake manifold… There wasn't much to clean. But I found out how the EGR enters the manifold; I thought it just goes into the major channels and probably gunk them up, but actually it has its own sub-manifold with little holes into each channel of the actual manifold. So the EGR doesn't actually muck up your intake, it only mucks up itself. That was interesting.



So I didn't achieve much by removing the manifold besides putting worm gear hose clamps on the PCV side of the hose. I put hose clamps on all the other hose connections, on the EVAP line.



So. Presently the engine continues to behave strangely intermittently. To recap, that is, it speeds up and down… on the freeway, on city streets, at low speed (especially noticeable then)… when slowing down it may stay running at high speed until when stopped; when stopped it becomes constant, staying running when it shouldn't be (battery full and not warming up). And it does that even in stealth with battery full, even coasting downhill, even when switching to NEUTRAL! But yeah when stopped (even in neutral) it runs constant, but when moving it ramps up and down… This strange, like, engine retardedness, is sort-of intermittent, like it may be like that then not be like that then be like that… but hmm, it looks like it begins happening after a while of driving; never happened soon after cold start.

I orginally thought it was behaving strangely because of the hose that popped off, but apparently it's the other way around. First the engine behaves strangely. During which presumably it somehow pressurizes the intake manifold. Causing the hoses to pop off. Now that the hoses are securely fastened, theoretically they will not pop off, and the car will not die, but the engine will continue to behave strangely, which I do not yet know why. (but yea hopefully it at least wont die again)

Soo... any ideas? No error codes or pending codes are logged when this happens. We've thought about an intermittently malfunctioning sensor. Or, during writing this post, realizing it only happens in the later part of trips, maybe it has something to do with heat??

 

oh btw; we've had similar issues before. First time something like this happened was a long time ago when i noticed the engine revving when slowing down on an exit: Engine runs when braking | PriusChat

Second time was when gas cap was apparently loose Engine behaving strangely and check engine light on | PriusChat (or was it really? cause that was a little odd… and then when gas cap finally failed to seal it did not have this issue IIRC P0171 P0441 P0455 | System too lean AND Evap leak detected | PriusChat)

Certainly never had hoses popping off the intake manifold before, though.

 

You are right, I should have left an accessible connection unfastened, maybe even slightly lubricated. I think it has blown something deeper in the EVAP system.

Today since cold start the system was wonky. I checked for pending codes and found the familiar P0441 and P0455 (large leak in EVAP system), which we've had before due to a badly sealing gas cap (OEM is poorly designed; threads bottom out before gap for gasket is fully closed) with the same behavior. That makes sense; EVAP is connected to intake manifold so a leak in the EVAP means an intake leak and thus engine wonk.

So I picked up a clamp at home depot and clamped the EVAP hose, and removed a hose clamp before it in case it pressurizes again. That stopped the engine wonk, though I thought I heard some fluctuation at higher speeds, but probably not.

So now I think the past engine wonk which would happen before a hose pop was caused by the hose loosening and leaking a little before popping off completely, rather than the engine behaving wonky causing the hose to pop off. Which means there are no noticeable symptoms accompanying the original issue.

The EGR cooler was recently just cleaned and is still functional. There is no engine rattle.

The PCV valve is screwed directly into the engine block. If it was blocked the pressure would be contained within the engine block, before the hose. But the top of the crankcase is connected to the rubber intake pipe, so it wouldn't be possible for it to build up pressure because it would just backflow into the intake? Or does it go though a check valve? Also, the manifold side of the PCV hose is not blocked either.

I just tested the flow from the dipstick tube with my fingers. I felt absolutely no flow, while the system is warming up at least.
Edit: After reading this thread I tested for blow-by by removing the oil cap while the engine is running, and oh! There is a lot of blow from it, I guess similar to a hair dryer on medium like they had.
Edit 2: Looks like that may be normal and not mean anything. I will consider using a pressure gauge on the dipstick. I have a water pressure gauge but may need some fittings to attach it.
If I still can't find the issue then I may try a compression or leakdown test. I also considered getting Techstream to diagnose.