Rough idle
09-15-2014, 05:35 AM
#2
AudiWorld Super User
Would start with a thorough check of the vacuum system. I had a similar issue with my A4 this weekend and turned out to be a broken one way valve in the vacuum system. Mine was pretty obvious because of the loud hissing sound when I popped the hood.
09-16-2014, 07:38 PM
#4
Hard to diagnose without the scan for codes but assuming the car drives with pretty much normal power, less likely to be electrical (spark plugs, coils etc) and more likely vacuum issues as the vacuum lines can fail more frequent as these engines get older.
Start checking the vacuum hoses (lots of them). Do this with the engine off as you need to try and visually check or at least run your fingers down the lines to check for splits, holes, and also check for tears at the hose clamp points. If you find a spot that may be leaking, start the engine and clamp the leak with your fingers, a change in idle indicates a leak.
There are lots of hoses, particularly around and under the inlet manifold so take your time. The braided ones get more exposure to heat so tend to have more failures than the rubber ones. The good news is the braided ones are also not particularly special so you can replace them with vacuum hose from your local auto parts store, the rubber ones tend to have shapes and need to be replaced with the correct part.
Next, with the engine idling, take off the oil cap, should be minor oil splashing about and some minor positive pressure, if you get a woosh (Technical term!) when you take the oil cap off start checking the PCV valve and crankcase vent lines, it may be blocked. If the PCV hasn't been changed before it will probably have the clamp type fittings so you need to grab a couple of hose clamps prior that you can manually tighten after inspection. Without any positive pressure, check the crankcase breather for holes, there should be some pressure when the engine is idling. A small amount of oil residue is common in these lines, if oil starts running out, your PCV is more than likely blocked or failed.
If still not luck, pull the spark plugs and make sure the gap is not clogged, pull the air filter and make sure it's not blocked.
That's about it for the no cost visual inspection without any codes to direct you further.
Start checking the vacuum hoses (lots of them). Do this with the engine off as you need to try and visually check or at least run your fingers down the lines to check for splits, holes, and also check for tears at the hose clamp points. If you find a spot that may be leaking, start the engine and clamp the leak with your fingers, a change in idle indicates a leak.
There are lots of hoses, particularly around and under the inlet manifold so take your time. The braided ones get more exposure to heat so tend to have more failures than the rubber ones. The good news is the braided ones are also not particularly special so you can replace them with vacuum hose from your local auto parts store, the rubber ones tend to have shapes and need to be replaced with the correct part.
Next, with the engine idling, take off the oil cap, should be minor oil splashing about and some minor positive pressure, if you get a woosh (Technical term!) when you take the oil cap off start checking the PCV valve and crankcase vent lines, it may be blocked. If the PCV hasn't been changed before it will probably have the clamp type fittings so you need to grab a couple of hose clamps prior that you can manually tighten after inspection. Without any positive pressure, check the crankcase breather for holes, there should be some pressure when the engine is idling. A small amount of oil residue is common in these lines, if oil starts running out, your PCV is more than likely blocked or failed.
If still not luck, pull the spark plugs and make sure the gap is not clogged, pull the air filter and make sure it's not blocked.
That's about it for the no cost visual inspection without any codes to direct you further.
09-22-2014, 09:35 AM
#6
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So I have the car in service position (t-belt Maint) , and went ahead and pulled the sai pump out, I unclicked the bottom hose, ( it goes to the Pcv if I'm not mistaken) , and fluid poured out of that, along with the pump that is filled with fluid as we'll! The fluid is like an exhaust condensation, and isn't oily or anything special. I would say the pump is done... Now what?
09-22-2014, 09:37 AM
#7
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So I have the car in service position (t-belt Maint) , and went ahead and pulled the sai pump out, I unclicked the bottom hose, ( it goes to the Pcv if I'm not mistaken) , and fluid poured out of that, along with the pump that is filled with fluid as we'll! The fluid is like an exhaust condensation, and isn't oily or anything special. I would say the pump is done... Now what?
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09-22-2014, 12:20 PM
#8
AudiWorld Super User
Code was P0411.
My understanding is this could be a deeper issue. The combi valve is supposed to open when the SAI is running to allow fresh air in. If you have water in the SAI, it is likely because the combi valve isn't working which then took out your SAI. So, you may have both issues.
My understanding is this could be a deeper issue. The combi valve is supposed to open when the SAI is running to allow fresh air in. If you have water in the SAI, it is likely because the combi valve isn't working which then took out your SAI. So, you may have both issues.
09-24-2014, 10:58 AM
#10
AudiWorld Super User
If you removed the SAI and plugged the combi, there would be reason to replace the combi. Why did you remove the SAI? Are you doing the vacuum removing "mod"?