[giblets46]

It is possible there is an issue with the MAF ( quite a lot of people seem to find it related to EGR issues (which can lead to too much gunk in the manifold)), try disconnecting that, and seeing if it effects it (will give you a warning light, but should run off a stored default programme). If this resolves the issue, it is your MAF. Might be worth taking it out and giving it a clean

Not a lot of help probably, but give all the connections a good clean, one may be loose, and possible that at a given temperature if may damage the signal .

Also clean off your MAP (as you have blanked your EGR, it will stop it getting worse), but will be covered in gunk, this also detects temperature of the air etc, and try spraying a little of the carb cleaner in the hole (may help release some of the swirl flaps).

 

[SP36]

I will give that a go tomorrow, if that doesn't work I'll remove the blanking plate. I just don't understand how that is temperature dependant? Surely if it's going to cause issues it would be all the time.

 

[SP36]

Unplugged the MAF for a whole day yesterday and problem still arised. It is definately temperature related. I did 3 journeys yesterday and it starts great and seems quieter then before the EGR partial blanking plate, thats for sure. It also more responsive under throttle.

I sat a a number of traffic lights idling yesterday and the revs would remain at 750rpm. Even when temp gauge read just under 90degC at around 88/89. Then as soon as the needle gets to 90degC it starts to feel **** under throttle and the revs bounce at idle.

Surely the EGR blanking plate would cause this issue no matter the temp? But then I don't see how the potential of a thermostat problem would cause this?

 

[Burnsy]

the ecu switches how it manages the engine / emissions once warmed up, hence MOT emissions tests are done after engine is at running temp. This means it treats both the MAF and Lambda sensors differently.

A bouncy idle on my 156 after it warmed up was (eventually!) found to be a duff lambda sensor.

perhaps the ecu need to relearn the engine mapping after the change, though I haven't heard that reported before. Maybe the egr blanking has just changed the eng mgt enough to start to show up this other problem which could've been there before... or it could just be coincidence.

You could try removing the blank again see what happens, though if back to normal then it doesn't tell you why blanking the egr caused it, but would point to it being air/exhaust related.

if you can get ecuscan or similar plugged in, you can watch MAF and lambda signals as car warms up to see if either is functioning abnormally - that would be my next step.

if disconnecting MAF made no improvement I doubt it's that.

 

[SP36]

Okay good call.

I'll do this at cold start & at operating temp with the blanking plate as well as cold and warm without & see if the signals are different.

I imagine the MAF signals will differ with the blanking plate due to compensating for the lack of dirty air with clean air?

Any idea what the 'normal' parameters would be for the Lambda & MAF?

How do you do an ECU reset? Disconnect batter for an hour or so?

 

[Burnsy]

not sure about MAF - ecuscan may show the normal top/bottom parameters.

Have a look here for lambda signals
http://www.alfaowner.com/Forum/alfa...6-v6-temp-and-idle-problem-4.html#post1678583

think you're right about the ecu reset.

good luck

 

[SP36]

not sure about MAF - ecuscan may show the normal top/bottom parameters.

Have a look here for lambda signals
http://www.alfaowner.com/Forum/alfa...6-v6-temp-and-idle-problem-4.html#post1678583

think you're right about the ecu reset.

good luck

Cheers burnsy very useful info. Are these reading generic or for the specific engine you had at the time?

 

[giblets46]

Bit confused here, the MAF should not change much at all with the EGR, the MAP will however as it in in the manifold right by the EGR.

 

[Burnsy]

readings for 156 v6, but think they're pretty much same for all, though not sure if any difference for diesels.

gilbets - I thought MAP was just another name for the MAF!?

 

[giblets46]

MAF is bottom left hand corner of the engine bay, measures air temperature etc (just after the air filter), normally a hot wire measure. The MAP is in the manifold, measures the temp and pressure in there ( as you have a turbo and EGR affecting temp and pressure) .

Have a look at the thread below, has links to each of the usual suspects on.....which one had you disconnected?

http://www.alfaowner.com/Forum/showthread.php?t=367560

 

[SP36]

MAF is bottom left hand corner of the engine bay, measures air temperature etc (just after the air filter), normally a hot wire measure. The MAP is in the manifold, measures the temp and pressure in there ( as you have a turbo and EGR affecting temp and pressure) .

Have a look at the thread below, has links to each of the usual suspects on.....which one had you disconnected?

http://www.alfaowner.com/Forum/showthread.php?t=367560

Thanks Giblets I used that thread to clean the MAP & EGR over the last few weeks. Very helpful.

I'm confused over this as well. I just don't see how I could essentially have a temp related EGR issue, or how the thermostat could effect the combustion process causing the car to rev at idle at operating temp. I'll see what readings ecuscan bring up over the next few days.

 

[SP36]

Right, first test done - EGR partial blanking plate & cold start.

I'll post up the graphs when I have all 4. But I always check my DPF clogging when I link up to ECUscan and about 10 days ago it read 96% but normal clogging, today it read 25% which I though was strange because I hadn't done the DPF cleaning run I usually do when seeing it clogged like that, I'd also done nothing but short 20-30min max, stop/ start town journeys since then. But my last regen was 12km ago which would have been yesterday, and my last 2 regen distances of 58km. So I am guessing and hoping that over the last week or so the car has been trying to do regens but not completing them, hence the rough idle and no power and it would explain why it only happened at operating temperature. I haven't driven the car today but ECUscan states no clogging so I'm hoping that is that and it was nothing more than a low speed regen that could never complete. I'll update after my next drive.

 

[SP36]

Was going to remove that attachment but oh well. Only thing of note is that the actual air intake quantity is 200mg/i more than the desired air intake quantity, but like mentioned above this could be down to the fact it is getting less dirty air from the EGR.

 

[sussexa]

Yes that data confirms that your egr is completely blanked, ecu is expecting around 300mg through maf and 185mg from egr flow.
As your blanked you have the full 485mg being drawn through the maf.
Or you havnt logged long enough to where egr operates, after a few mins after start and cycles every 2-3mins at idle on off, as last post says partial blank?

 

[SP36]

It's a partial blank. You can't really see from that graph but the EGR was just under 4% open. I only tested for 60 seconds.

So I don't think this issue was DPF regen related as it was happening on my way to work eariler with no other regen signs (turbo gauge dropping fast/ low mpg).

I'll do the warm test when I get home & build a graph from the data after my car has warmed up from the drive home. I'll then remove the EGR blanking plate later in the day and conduct the same tests.

Really annoying because I like the way the car drives with the blanking plate, until it reaches operating temp that is.

 

[SP36]

Well I've completed all my tests and it makes no difference with or without the EGR partial blanking plate, so that will go back on because it started and accelerated better with it on.

I also did a google search today (because taptalk won't search any more on my phone :-S) and got much better results then doing a search via the forum...

Anyway, I found this...
http://www.alfaowner.com/Forum/alfa...r/344032-erratic-idle-cured-159-2-4-jtdm.html

Same issue and was solved after a throttle body clean. So since I know I have inlet manifold issues I'm thinking it could be simply this. I also found a thread where Alfa had diagnosed it as a bad air re-circulation gasket, and since this started happening after I took the EGR off, that is also a possibility.

So as I need the inlet manifold replaced anyway I'm going to get that done next week as I got a fault code and limp home today while accelerating to 80mph only briefly which tells me it's getting worse, especially considering my idle issue could be related according to the above thread. Also while it is in I'm also going to get them to replace the Thermostat as my heaters aren't as hot as they was, which hopefully should resolve the coolant related fault code I had recently. Also my fan kept kicking in today. I'll also get them to check the water pump while they are at it, but after 3.5k I hope is hasn't died because that is just shocking.

I'll update whether or not these issues get solved by the work ( I bloody hope so!!!)

But if anybody is interested, I've attached the graphs from the 5 tests. All done over 2 minutes (except graph 1)

Graph 1 is Blanking Plate from COLD

Graph 2 is NO blanking plate from COLD - Not much difference between the 2.

Graph 3 is Blanking Plate from WARM 90degC - This is interesting because you can see the high spikes and fall in air intake and requirement ever second or so which calm when the EGR closes...

Graph 4 is NO Blanking Plate just under operating temperature (about 83degC) - The idle didn't feel perfect but aside from the odd spike in required air quantity all seems not TOO bad.

Graph 5 is NO Blanking Plate from WARM 90degC - Lots of spikes!

Graphs 1, 2, 4 and 5 have a EGR opening of 3.98%. For this reason I am ruling out EGR because it seems to have no impact (expect for on graph 4). I tried doing an EGR actuator test on ECUscan which failed due to "conditions not being right". What these conditions are I don't know.

 

[sussexa]

Conditions for egr check may be engine not running, without removing egr to watch during test you will prob just hear clacking of valve.
Most jtds seem to show 4% when the valve is fully shut.
One of those logs (3)shows valve open (guessing 30-40%) but the airflow doesnt seem to follow quite right as valve shuts airflow smooths out but doesnt go any higher, egr opens again airflow up n down again.
Is there any chance of a leak at egr gaskets.
Id expect 485mg egr 4% and 285-300mg with egr open 30-40%.

 

[SP36]

A leak is highly possible. A thread I found earlier with similar symptoms Alfa diagnosed as exhaust recirculation gasket. That and the inlet are my only leads. I'll see about replacing any gaskets.

Is there supposed to be 2 gaskets?

When I removed it there was only one going to the manifold, is there supposed to be one on the pipe where the gases enter the EGR?

 

[sussexa]

Yes should be a thin metal gasget there also.