1.6 BSE engine rough idle [solved]

[pyro]

Hi all,

My 2008 Leon 1.6 petrol (1p1) engine code BSE has been misfiring on idle for the last few days.

When on higher revs and normal driving it seems to run fine. On idle it knocks, misfires and generally sounds terrible. Idle is around 650rpm which is lower than usual.

When the engine is cold it runs ok, but as it warms up it starts to have problems.

I've tried changing the ignition coil but that has not worked.

I unplugged the front lambda sensor but that didn't affect anything. Will be trying the rear one later.

The error codes are suggesting it is running lean which I'm not too convinced about as it smells like it's running rich.
P1141 - load calculation cross check, implausible value
P0171 - system too lean

Does anyone know what the issue could be?

 

[Legojon]

When did it have a new fuel filter last? I assume you checked the plugs while you did the coils? Getting it scanned and determining which cylinders are misfiring would help. Maybe a fuel injector on it's way out.

 

[pyro]

Thanks for the reply.
The fuel filter was changed about 2 years ago and it's done less than 5k miles since then.

It's misfiring on all cylinders, I have checked with the cable and vagcom/rosstech software to track all of that kind of stuff. It wouldn't be an injector if all four are misfiring?

I didn't check the plugs, they were done last year. Will check them now.

The engine will actually stall the revs are getting low enough.

 

[Legojon]

Have you tried unplugging the maf sensor while it idles to see if it sorts itself out?

 

[pyro]

My engine doesn't have a MAF, only a MAP sensor.

I can only get to plugs 1 and 4 easily, they are both showing signs of running lean.

 

[pyro]

It's probably not the MAP as we checked the readings and it was reading correctly, i.e. about 1000 when engine off, about 450 during idle, 300 or so during throttle.

 

[pyro]

So the problem ended up being a busted intake manifold seal. There's a rubber seal that fits between the two sections of the upper and lower intake. One of those was shredded, possibly from where it was not correctly reassembled last time and got pinched. This was letting in air and causing the rough idle. The part number is 06A 133 227 D (original was B) and costs about £11 each.

Once changed, the car is running better than it has since I bought it. The MAP sensor is now reading about 330mb at idle, well within spec compared to the 470mb before, which was just outside spec but we thought that was ok yesterday (spec was 300-450).
We changed the front lambda sensor (behind the back of the engine on the exhaust manifold), and the ignition coil earlier in our attempts to fix it. Both of these were not strictly necessary for this particular issue but we found the coil needed to be replaced anyway as there was a hairline crack in it and two of the four connections had oxidised, and the lambda was reading an incorrect resistance across two pins compared to the new one I bought so it needed doing too.
We also noticed the bolts holding the throttle body were slightly loose. Tightening them up made a small difference, so check that as well if you are having problems.

Hope this helps anyone in the future.

 

[pyro]

Added some photos of the old seal and the new replacement.

 

[Stakill]

Just went through the trouble of creating an account to thank you. Not necessarily because this is what is causing my problem with occasional missfires (my intake manifold was never off), but because people usually never ended up writing up what caused their problem, even though it might set someone else on the right path too (even when the underlying issue is different). So, thanks!

 

[R3k1355]

Manifold might not have to had been off for the seal to perish. Rubber only lasts a certain time on an engine before it's needing replacement.

 

[Stakill]

Yeah, definitely. My problem turned out to be a bit of corrosion between the wires #1 and #3 and the ignition module.

The seals on the air intake were surprisingly soft and in good condition (never been removed, 12 years old, 140,000 km).

Replaced everything (spark plugs, leads, ignition module, intake seals both top and bottom). The car is as good as new now.

 

[nakovgeorgi2000]

So the problem ended up being a busted intake manifold seal. There's a rubber seal that fits between the two sections of the upper and lower intake. One of those was shredded, possibly from where it was not correctly reassembled last time and got pinched. This was letting in air and causing the rough idle. The part number is 06A 133 227 D (original was B) and costs about £11 each.

Once changed, the car is running better than it has since I bought it. The MAP sensor is now reading about 330mb at idle, well within spec compared to the 470mb before, which was just outside spec but we thought that was ok yesterday (spec was 300-450).
We changed the front lambda sensor (behind the back of the engine on the exhaust manifold), and the ignition coil earlier in our attempts to fix it. Both of these were not strictly necessary for this particular issue but we found the coil needed to be replaced anyway as there was a hairline crack in it and two of the four connections had oxidised, and the lambda was reading an incorrect resistance across two pins compared to the new one I bought so it needed doing too.
We also noticed the bolts holding the throttle body were slightly loose. Tightening them up made a small difference, so check that as well if you are having problems.

Hope this helps anyone in the future.

Good day sir!
I own a Golf 6 with the very same 1.6 BSE. I am curious about how your engine behaves at working temperature. Is the idle now so smooth that you can leave a coin straight on the engine or it still moves a little bit? Some claim 1.6 BGU/BSE shake a little since new. Cheers!

 

[nakovgeorgi2000]

Just went through the trouble of creating an account to thank you. Not necessarily because this is what is causing my problem with occasional missfires (my intake manifold was never off), but because people usually never ended up writing up what caused their problem, even though it might set someone else on the right path too (even when the underlying issue is different). So, thanks!

And how is your engine running now at hot? Still shaking a little or completely smooth?

 

[SV0]

hi although i have audi a3 1.6mpi BSE i am experiencing the same problems but on cylinder 3 checking with vcds shows intermittent misfire 3
this issue happens rarely, once every 4 or so months. but this week it hasn't gone away, can someone tell me as to what they replaced (images/links dont show anything anymore)
cylinder 3 spark plug is also much darker and the exhaust pipe gasses dont flow smoothly (sort of cuts in and out)

 

[mty12345]

hi although i have audi a3 1.6mpi BSE i am experiencing the same problems but on cylinder 3 checking with vcds shows intermittent misfire 3
this issue happens rarely, once every 4 or so months. but this week it hasn't gone away, can someone tell me as to what they replaced (images/links dont show anything anymore)
cylinder 3 spark plug is also much darker and the exhaust pipe gasses dont flow smoothly (sort of cuts in and out)

If it has individual coil packs for each cylinder, then swap cylinder 3 with another coil pack, and see if the misfire moves cylinder

 

[n3utr1n]

Hi everyone,
I have followed this thread hoping to solve my issue but i feel the need to ask you guys to update if any of you having idle issues have solved the mystery.

What i've done so far:
1. Removed the intake, cleaned everything and changed all rubbers.
2. Replaced coil pack, coil links and sparkplugs.
3. Checked for any air leaks on the intake manifold - no issues.

What i've done along with checking and changing parts:

1. Reset throttle body and re-adapt
2. Checked timing belt retardation (oscilates between 9-11°)

After all i noticed the idle is still not ok. Engine shakes a little bit, noticeable with ac off.
Also if the ac is on, revs are little higher and there is no (or rarely) misfire on cyl 3.
When ac is off idle goes lower than 836rpm (which i found to be the default value) and misfires are continously present on cyl3 only (1 per second ruffly).

So.. my question now is, where should i look next?
I saw previously other pointing to thermostat, but i have no issues with coolant and symptoms are present regardless the engine temp.
Others were pointing to brake vacuum, but i also do not understand the relation between cyl3 and brake vacuum...

Please help!