Irregular idle, warm engine
#1
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I'm observing a new issue since a few days : after driving for a little while, engine warm, the idle is a little rough and when starting from 0 it stutters a bit like it's going to stall (but doesn't).
The symptoms are not felt at higher rpm.
Among the possible causes for this would be a compression issue (haven't tested that yet), however this morning I had my obd reader plugged in (an iCarsoft 930) and exploring the data streams I inadvertently triggered a P1798 error, all errors cycling on the dashboard : gearbox fault, low brake fluid, etc.
This disappears when restarting, so I wasn't worried, however: the rough idle symptoms disappeared when it happened.
So I'm guessing this is related to a sensor and isn't a mechanical problem.
- I've checked the air intake for leaks -- looks airtight. (including the britlle breather tube)
- At idle, the MAF reads 8+ g/s when the engine is cold, around 5.6 g/s when hot, which seems normal.
- The values I'm getting for the coolant and air intake temperatures are respectively -40° C and +66° C, which sounds ... not right. But I suspect it's more of a reader issue, because the engine temperature on the dashboard is normal, and when hitting the "Ext" button on the A/C panel I'm getting the correct value as well.
- At idle, LTFT are -2.76% on one bank, -0.79% on the other. Is that normal ?
What other sensors and numbers should I check to properly identify the culprit ?
The symptoms are not felt at higher rpm.
Among the possible causes for this would be a compression issue (haven't tested that yet), however this morning I had my obd reader plugged in (an iCarsoft 930) and exploring the data streams I inadvertently triggered a P1798 error, all errors cycling on the dashboard : gearbox fault, low brake fluid, etc.
This disappears when restarting, so I wasn't worried, however: the rough idle symptoms disappeared when it happened.
So I'm guessing this is related to a sensor and isn't a mechanical problem.
- I've checked the air intake for leaks -- looks airtight. (including the britlle breather tube)
- At idle, the MAF reads 8+ g/s when the engine is cold, around 5.6 g/s when hot, which seems normal.
- The values I'm getting for the coolant and air intake temperatures are respectively -40° C and +66° C, which sounds ... not right. But I suspect it's more of a reader issue, because the engine temperature on the dashboard is normal, and when hitting the "Ext" button on the A/C panel I'm getting the correct value as well.
- At idle, LTFT are -2.76% on one bank, -0.79% on the other. Is that normal ?
What other sensors and numbers should I check to properly identify the culprit ?
#2
#4
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Values seem to be normal, about 0.08-0.1 V on warm idle.
I unplugged the MAF sensor while the engine was running with that rough idle problem, which caused the engine to stall instantly. It started just fine afterwards, but I'm surprised : I expect a "restricted performance" amber light on the dashboard, no more.
I unplugged the MAF sensor while the engine was running with that rough idle problem, which caused the engine to stall instantly. It started just fine afterwards, but I'm surprised : I expect a "restricted performance" amber light on the dashboard, no more.
#5
#7
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So, downstream lambdas where steady at around 0.8V, looks about right.
From another thread, I figured it might be related to the coil packs because a few months ago a coolant hose exploded and flooded the engine. And indeed, the driver side coil packs and spark plugs holes were pretty dirty with half dried coolant.
I cleaned that up and it seems to be running better, not quite perfect yet but a significant improvement. I'll remove the plugs and clean more thoroughly (didn't want to have coolant fall into the cylinders and was in a hurry so it's not really pristine down there yet)
From another thread, I figured it might be related to the coil packs because a few months ago a coolant hose exploded and flooded the engine. And indeed, the driver side coil packs and spark plugs holes were pretty dirty with half dried coolant.
I cleaned that up and it seems to be running better, not quite perfect yet but a significant improvement. I'll remove the plugs and clean more thoroughly (didn't want to have coolant fall into the cylinders and was in a hurry so it's not really pristine down there yet)
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