P1553 and P1504 coming in and going out

[tyy990]

It's 2004 Fabia, 1.4 with BBY engine.

 

That all started after a major engine overhaul. I replaced all pistons (one was worn out and made a clanking noise). Other than that noise the car was running fine before the overhaul. So now after I reassembled it and started it it ran perfectly fine for a couple of minutes and then all of a sudden I got a rough idle and the EPC light on followed by the traction control light. Then idle went completely insane fluctuating between 900 and 1200rpm and not reacting at all to the gas pedal.

 

So I double checked the timing, vacuum, cleaned the MAP sensor just in case but there was no change. Then I disconnected the EGR connector while the engine was running and it immediately started running almost fine and reacting to the gas pedal. So I removed the EGR and soaked it for a while in brake fluid. Then I put it back and the car was idling fine. It warmed up then I drove it around the block and it was all fine. Just as I parked it I got the dash lights again and the same errors. So, I blamed it on the EGR and got a new one.

 

After replacing the EGR I got very similar experience. It was running perfectly for a while then I got the dash lights and then it got to its initial state - weird idle and no reaction to the gas pedal. 

 

I am really dumbfounded now. I have double checked timing, brake vacuum hose, EVAP hose (blocked that too), PCV hose...nothing. I have VCDS and I have ran adaptation for throttle body and EGR. Nothing changed.

 

It looks like a vacuum leak in a way since when the car seems to run fine idle is at 880rpm (BBY engine so it should be 680) but I really cannot figure out how it get better and worse like that. In general when I manage to trick it into running fine it could idle fine for hours without getting any errors. Errors only emerge while driving.

 

The MAP senor shows 0.4 bar at idle and 0.97 bar with engine off. The latter seams fine but I am not really sure about the former.

 

So there are three questions at this point:

1) What MAP readings do you guys get at idle? Is 0.4 bar normal?

2) Am I missing some possibility for a vacuum leak?

3) Could this be something else?

[TMB]

I know you've checked the servo hose but they can crack at the bottom out of sight. Worth having a really close look.

[Breezy_Pete]

I see about 0.3 bar at idle.

It's not clear from what you've written what you did with the PCV hose? Ideally, to eliminate it from your enquiries, you should disconnect it from the inlet manifold and block the hose stub it goes onto. Maybe you did do that?, it sounds as though you are quite methodical.

 

Auto or manual gearbox?

Edited 13 June, 2020 by Wino

[tyy990]

I disconnected the PCV hose and checked its integrity. I did check all the vacuum hoses on all sides. I haven't blocked the PCV hose yet and that is something I would do.

 

@Wino you mention in another topic a pressure equalizing port on the PCV body. Where is that? Is it where the arrow points here - 

 

I mean the PCV used to work just fine before the overhaul but it might have gone bad now by very unlucky coincidence. 

 

0.4 bar is 30% more than 0.3 bar so maybe I really have a vacuum leak. But I really cannot figure out how it comes and goes like that. Or it might be ECU or MAP sensor failure.

 

Argh, that was not really supposed to be that complicated. 

[tyy990]

Another thing I forgot to mention - the car spent like 8 months partially disassembled waiting for me to find the time to complete the project. Does something on these cars go bad or stuck from sitting around and not being driven?

[Breezy_Pete]

Haha, I only read a preview of your post without seeing your photo. I just edited one of mine to this:

 

[dant158]

I'm currently having potentially similar problems with my Fabia 1.4 BBZ.

 

No recent overhaul or anything, but have been having intermittent issues with codes P1553 and P1504 (amongst others) for some time now. Just today was driving on the motorway and had the EPC/Check engine lights come on, along with the ASR light, and loss of throttle response. Managed to pull over to the side and wait for a few minutes. Tried restarting a few times and got the same response you mentioned in the original post (she would fire up, but rev hunting like crazy with the throttle making no difference). Then after a minute, she fired up just fine, (engine and epc lights still on, but no ASR) and got us home.

 

I've been tinkering around within my very limited experience/expertise working with cars. Cleaned the throttle body and adapeted it, cleaned the MAP sensor checked the lambda, etc, but to little avail. Such seems to be the problem with these intermittent faults; difficult to tell if you've actually fixed it, lol

 

One interesting thing I read and was going to try next was about the thermostatic control of the hot air/fresh air intake flap in the engine cover. I've seen a few posts indicating that the thermostat/piston/flap/spring the assembly can fail and lead to hot air being drawn into the intake, instead of cold air, leading to all sorts of issues. it seems some people have gotten a lot of benefit to 'fixing' the flap in the closed (fresh air intake) position. 

Ref: 

 

 

Potentially worth exploring? Apologies if this is a bit of a hijack, but I came on to make a post about this, but then seen your fault codes on the front page already

[tyy990]

No hijack really. Is not the case in my case though since I get this behavior with the cover removed and throttle open to atmosphere.

[tyy990]

Well all in all that was solved by resetting the ECU to factory defaults by writing value 00 to channel 00 in the engine control module. I really can't believe the ECU needs to be reset and cannot figure out but itself something has changed. But that's what really fixed the problem.