Hey all, this is my first post on these forums, and I've been reading it for weeks as it seems better than the haynes manual for advice! 

 

I bought the car (51 plate 1.4 mpi) a few weeks ago with no MOT, 59k miles, for £400. I put it through an MOT, and with 4 new tyres and a new spring it sailed through. It seems to have an idling issue, which is worse when hot, although it is a bit shakey normally. Sometimes when the car has been used a few times, it stalls when it has come to a halt (Eg. at traffic lights). I recently changed the coolant temperature sensor, and the thermostat (the old one was broken). This seemed to make the car slightly better, but an hour ago it stalled when I came to a halt. If I start it when its warm, the revs go 1000, then drop to about 600 (engine sounds like its struggling) then it returns to normal, and seems to be fine. After it had stalled today, I drove it home (no problem, seems to perform fine) and then when it was sat in the driveway I revved it to 2000 then took my foot off, it went 2000, 600 (STRUGGLE) then returned to normal. It repeated this after even the smallest rev. Later on I did this, and it just dropped to ordinary revs without the struggle.

 

I have taken the throttle body off (I'll give it a clean) and I'll post some pictures of what it is like now, if someone could tell me if it looks OK or not that'd be greeeaaat . I've read it might be the idle air control valve, so thats the next step.

 

Bottom of the throttle, looks pretty oily. There is some oil in the inlet manifold too.

 

Top of the throttle.

 

Finally, I saw there was a pretty battered looking tube going into the back of the inlet manifold, with a crack at the entrance. I think its brake related, and I read somewhere that this can cause stalling problems? It does make a sort of low whistle as it speeds up, which I assumed was just the noise the engine makes, but I guess it could be the brake vacuum thingy. The MOT guy did reckon the brake pedal poked out a bit far, but he let it go. I  can't see how this'd be heat related, and I imagine this is irrelevant. I'll post a picture though.

 

This is the entrance to the manifold, looks pretty cracked

 

This is where that pipe enters the brake thing (drivers side of the engine) This area looked a bit damp around the pipe entrance earlier, no idea if this has any relavance.

 

Sorry for the essay, and thanks SOO much in advance for your help. I am at a loss with what to do. It's an annoying fault, because otherwise the car performs and drives beeaaautifully.

 

Cheers,

Tom.

That pipe is the vacuum pipe for the brakes.

 

Start by getting that changed.

 

It can cuase stalling problems or even loss of braking assistance.

 

Quite common on the fabia.

 

Phil

Yep, heat will make the pipe softer, more flexible and so leakier at that cracked area.

 

Throttle body looks like it has been cleaned pretty recently.

Ok, thanks! I'll order a new tube now, Is it relatively simple to just swap the tubes? Ah I hadn't thought of heat making the pipe leakier! Could this pipe be the cause of the brake pedal being too high, and the whistling? I'll get back to you once I've done this.

 

Thanks very much,

Tom.

Quick question, the brakes have never actually felt like they're performing worse than they should whilst driving. Does this change things?

 

Cheers

Tom

You'll likely find that you get more stopping power for less leg effort once you've fixed that pipe.  You should definitely fix it, even if it actually isn't leaking at the moment, as it's a potential safety issue.  If it completely fails you will suddenly find yourself with no servo assistance, and having to press the brake pedal a lot harder to stop.

 

I'm not sure whether it'll affect the height of the pedal, but I think the whistling noise will be it leaking so that should go away.

Hey! 

Right, I've put a new vacuum tube in, and the brakes seem to function absolutely fine. However, the problem with the revs seems even worse. I sat there with it idling, pressing and depressing the brakes, and the engine didn't really respond (tiny alteration in revs when I pressed and depressed, but I assume this is just the normal changes in manifold pressure. When I just left it idling, it sounded rough and struggly, but it stayed between 750-900, and didn't really think about stalling once.

 

However when I revved it a few times, it STRUGGLED, dropping to like 600 revs then 1000, then 600 etc. It didn't stall, but came so close that the battery light came on.

 

I think this is because I unplugged the throttle body when I took it off, does this mean I have to reset it with VAG-COM? If not, what do you think could be causing this? Its obviously gotten worse, and the two things I've fiddled with is the vacuum tube and the throttle body.

 

Thanks very much

 

Tom.

It also has the engine light on, along with a new fault code, something to do with the mass air flow/volume systems. Maybe I didn't install the vacuum pipe correctly, but I've done all the tests on the brakes involving pressing the pedal down and feeling the changes in resistance, and its passed them all. This is confusing... :S

Disconnect the battery for 30 minutes, ENSURE that everything is switched off, re-connect and leave to idle for 30 minutes without touching any pedals or switching anything on. This re-sets the ECU.

 

DB

Has the whistling noise gone?

According to the Skoda manual for the 1.4 8V engines, they have an Air Intake manifold Pressure & Temperature sensor

 

Both sensors are incorporated into a single sensor housing, fitted behind the throttle body.

 

I would suggest checking the connector, if possible plug in VCDS to test the sensors.

 

 

IMO thats where there could be a fault. as that measures the Intake manifold pressure and tempreture, and with those two readings you can calculate the volume of air in the manifold, and therefore how much fuel to inject. If its faulty it may cause incorrect fueling.

 

If you have a physical air leak in the system the Lambda/O2 sensor would trigger an EML fault saying the system is running too lean.

Thank you I'm now resetting the ECU.

 

Yep! The whistling has vanished, cheers for that advice, the other side of that cracked tube was even worse, so whether that was the problem or not, it would have gone very badly wrong soon enough! You may have saved my skin haha

 

Ahh I see, I'm struggling connecting it to vcds (port ok, interface not found), but it connects to easy obd fine, and thats where I got those fault codes. I also checked live data readings, and the manifold pressure reading was 52-55. Not sure if this is a normal value or not. The problem has gotten markedly worse since fixing the vacuum hose, reckon this is just the throttle body being out? Or would fixing the leak make the sensor worse? Thanks for your advice!

 

Finally, what about the idle air control valve? I couldn't find anything about it in the haynes manual, but I've seen it referenced online loads. Could this have anything to do with it?

 

Thanks very much for your help everyone, I feel like I'm making progress!

 

Tom.

I have a feeling that mogwye's advice will see things return to how they should be.

Do a throttle body realignment if the battery disconnect doesnt work (tut on ross tech wiki). 

 

 

To Test the Intake tempreture sensor:

 

Go to "measuring blocks - 08"  -> Group "004", then there should be 4 boxes. Engine Revs, Battery Voltage, Coolant Temp, Intake Manifold temp.

 

You need to be looking at the 4th value, i.e the Intake manifold temperature. If it doesn't change at all and does not make sense (i.e reading -40 degrees Celsius) then there is an issue with the sensor/wiring.

 

 

To Test the Intake manifold Pressure sensor:

 

Go to "measuring blocks - 08"  -> Group "003", then there should be 4 boxes. Engine Revs, manifold pressure, Throttle position , Ignition Advance/Retard (an angle)

 

This time you want to be looking at the 2nd value, it should be between 350 mBar and 600mBar. Again if it is stationary and does not change then it could be a fault with the sensor/wiring

Yeah I saw on one thread that the battery disconnect method is a bit hit and miss! I hope it works, that'd save a lot of hassle!

 

I'm struggling with connecting a third party plug to vcds, but I'll get that cracked and check those sensors asap! I'm confused as to why the problem would have gotten worse after the tube was replaced, but I'm definitely not ruling it out!

 

The intake manifold had a bit of oil in it, not pints of it, but enough that'd it would pour out if I tipped it. Could this have anything to do with it? PCV or something?

 

I'm still halfway through this ecu reset, but I'll get back with the results.

 

Thanks,

Tom.

because that pipe connects the brake servo to the intake manifold as the intake vacuum assists the servo's operation. So the crack in the pipe would be allowing air to get into the engine bypassing the throttle body. if the pressure sensor was faulty, and was reading a higher manifold pressure (although still under 1 Bar) it would be fuelling to as if there was more air in the system then there actually was. So in a normal situation it would over-fuel, but because of the crack in the pipe it was allowing extra air in making it fuel closer to the actual amount.

 

But this is all speculation and you wont know until you can measure those blocks.

 

One quick question, when you removed the throttle body did you replace the red gasket and tighten the 4 bolts to the same Torque?

Sounds like an excellent theory mate, definitely makes sense!

 

I used the same gasket (it looked ok) and I couldn't find my torque wrench so I just tightened them to about the same feeling. Was that a stupid thing to do? Haha :S I found the torque wrench now, should I redo it? Would it have this big an effect on the engine running?

 

Thanks

Tom.

Right,

The ECU reset didn't work, it doesn't seem to have done anything. The engine idled beautifully for 30 minutes though, so the fault definitely lies with acceleration! I'll spend tomorrow sorting out my car interface with vag-com, so I can check those sensors and reset the throttle body.

I just used a friend's posh vw/audi scanner, and it came up with the following fault codes:

 

- 16500 (P0116) Engine coolant temp sensor implausible signal. (I recently replaced the coolant temp sensor, so I guess this is an old fault code)

- 17549 (P1141) Load calculation cross check - implausible value.

 

Not sure if this means anything, I'm picking up vibes of my MAP sensor thing being broken!

 

Thank you

Tom.

Throttle body adaptation needs doing.

Will that be whats throwing up the fault code then? I'll do that the moment I've got VAG-COM up and running!

 

Thanks very much!
Tom.

from the second fault code 17549

 

http://wiki.ross-tech.com/wiki/index.php/17549/P1141/004417

 

i suggest you read that page.

from the second fault code 17549

 

http://wiki.ross-tech.com/wiki/index.php/17549/P1141/004417

 

i suggest you read that page.

 

Errr, Taylor93, he's already corrected those problems, he just hasn't got VCDS working yet so he can clear the codes and re-adapt the throttle body. The car is otherwise fixed now.

VAG-COM cable should arrive in the next hour or so. Going to remove the throttle body again to clean it, and maybe also clean the MAP sensor. Then I can torque the throttle body back on properly (oops :P).

 

Once thats done I'll adapt the throttle body and pray that the car works!

 

Cheers

Tom.

Right, just adapted the throttle, and I think she's fixed!

The idle is still a little lumpy, with the needle moving up and down a little bit, but there was none of that crazy stalling business. I think the lumpy idle is a 1.4 mpi "thing" so I guess I'll learn to love it haha.

 

Thanks SOO much for everyone's help!

 

Tom

Glad it's sorted.

 

Yeah the 1.4 MPi is a little lumpy anyway.

 

It's basically the same as the 1.3 mpi in the felicia and that's the same.

 

Changing a slightly worn timing chain can help.

 

Phil