My S4 has a rough idle and DIESELS on shut-off!!!

[caall99]

My S4 is having a hard time shutting off exactly when i want it to. It seems to diesel for a second or two longer and doesn't sound to healthy. car has 116,000 miles on it. It also has a randomly occuring stumble during idle that shakes the car. it's somewhat subtle, but can also be heard through my aftermarket exhaust.

would a carbon deposit problem cause such symptoms in an S4?

i am leaning towards steam cleaning the inside of my motor with some water, and using the front vacuum port that connects to the two DVs as the injection point. any input in regards to other maintenance i should be doing? spark plugs, MAF, DVs, TBB, etc... all that stuff has already been replaced.

btw, car has no boost leaks and feels very strong with the pedal to the metal!

[tike0rz]

Vag it and log for misfires...mine had some very subtle ones as well. Log blocks 015 and 016

[caall99]

cool thanks!

was wondering how i could log miss fires. is it a counter system? (counts how many missfires within a time interval) do you think carbon deposits could be at fault? any ideas on the dieseling on shut-off?

[AudiTechS4]

hmm what about leaking injectors. crimp off your return line for fuel and shut your car off.let it sit for a bit and disconnect your return line if fuel doesnt spray all over :) you have a leaking injector. or pull your fuel rail and key on and off a few time to prime the fuel rail with pressure and see if an injector is leaking

[gmann]

hmm what about leaking injectors. crimp off your return line for fuel and shut your car off.let it sit for a bit and disconnect your return line if fuel doesnt spray all over :) you have a leaking injector. or pull your fuel rail and key on and off a few time to prime the fuel rail with pressure and see if an injector is leaking

I was thinking the same thing... that's about the only thing that will cause dieseling of a FI car.

[AudiTechS4]

yeah any car running on needs fuel. only a leaky injector or injectors can cause that

[Blake260]

I have a similar problem with my car, although is seems like yours is worse.

I changed my spark plugs, and seamfoam the intake mani and fuel.

no change is misfires/rough idle.

I am going to change out all the coilpacks, and hopefully that will get rid of them.

[caall99]

check this out.

I did some vag logging of my car and it turns out that i sometimes get 1-2 missfires per minute in cylinders 2,3 and 6. again, nothing major but the subtle missfires are there. car does not rev 100% smoothly, there is some noticable choppiness in the lower RPM band.

another vag com scan measuring "cylinder voltages" yielded some interesting results. i am guessing "cylinder voltages" are the voltages from the ignitor to the coil packs?? i feel i might be completely wrong in my assumption but then again this next bit might prove me right. It appears that cylinders 1-3 have a common voltage of .6V and cyls 4-6 have a voltage of .9V (on average). my two ignitors are different colors (one is yellow and one is black). could there be some sort of ignition imbalance across my motor? i just want your input on this and maybe some of you could do an "advanced measuring block" scan for cylinder voltage. Its in the list that pops up when you go to advanced measuring blocks under the Engine - Control Module.

Picture showing voltages of all cylinders on a short drive through town. (sorry about shit quality, but cyls 4-6 are the highest three lines, cyls 1-3 the lower three)

[caall99]

another update... here are the missfires. my short logging trip started with the car cold and ended with it at normal operating temps. i never drove it hard. something is messed up here. plugs? injectors? ignitors? coil packs? what else could it be?

[RenegadeEngr]

I'm interested to know as well.

[caall99]

True story... but no one is saying anything...

[DxC]

what measuring block are you measuring in vagcom? are you logging this during closed loop fueling (normal driving) or open loop (WOT)

misfiring could be your plugs, could be bad gas, could be carbon deposits ... etc etc

just start troubleshooting step by step

[gmann]

what measuring block are you measuring in vagcom? are you logging this during closed loop fueling (normal driving) or open loop (WOT)

misfiring could be your plugs, could be bad gas, could be carbon deposits ... etc etc

just start troubleshooting step by step

Yeah, start at one spot and go from there.

My suggestion before you buy anything. Start the coil pack swap. ie swap coil pack 1 and 6 and see if the misfire goes follows the coil or stays with that cylinder.

[///M3 TO S4]

i bet you have a major boost leak. My F-hose came partially un-done....and it idled exactly like you're talking about. Check your f-hose. Its at the front of the intake manifold, right behind the passenger side DV. It might be torn if you have a stock one still, and if you have a samco one like me, it just might have worked it's way loose.

[Muck_and_Grind]

I have the same problem and am tearing my engine apart on sunday. it is a blown head gasket for me anyways

[caall99]

what measuring block are you measuring in vagcom? are you logging this during closed loop fueling (normal driving) or open loop (WOT)

misfiring could be your plugs, could be bad gas, could be carbon deposits ... etc etc

just start troubleshooting step by step

logging 15-16, those logs were on boost and off boost, but nothing all out full throttle for the missfire logging anyways. car feels great on boost and high rpms. its below 2k that i get some weird inconsistencies. sometimes, once in a blue moon i'll get one massive missfire that essentially makes the whole car shutdown for a split second. like a huge stutter. Its not repeatable and happens randomly.


i think i may have to do some part swapping. one ignitor, ie. ignition control module on the air box, is yellow or brown (can't remember off the top of my head) while the other is black.


On a final note: the car has been maintained meticulously in the past, and driven normally. the previous owner did not beat on the car. i truly believe it's a part wearing out/breaking due to age and mileage (116,000) i replaced the plugs with regular copper ones 3000 miles ago and gapped them down. it might be time to check on them. with all my egt, o2, maf and boost leak issues, it may be that they are fouled by now.

i bet you have a major boost leak. My F-hose came partially un-done....and it idled exactly like you're talking about. Check your f-hose. Its at the front of the intake manifold, right behind the passenger side DV. It might be torn if you have a stock one still, and if you have a samco one like me, it just might have worked it's way loose.

I fixed my most major boost leak, namely the TBB. i also replaced the MAF and put new 710n DVs in the car. i know a mechanic noticed that the f-hose had been replaced in the past. when i did a smoke test the only place it leaked from was the TBB, but then again the smoke may not have escape elsewhere because the tear in the TBB was so bad that it was quite obviously the point of least resistance for the smoke to escape from.

I have the same problem and am tearing my engine apart on sunday. it is a blown head gasket for me anyways

you're scaring me man. i am losing coolant somehow. very very slowly though, like an inch in height in the coolant expansion tank since i have owned the car. i bought the car last october, so an inch per year? please don't tell me it's the headgasket. i am def going to pressure test each cylinder this weekend.

[DoGGRoBBer]

As to the coolant loss, you have 2 other possible issues. Mild ones so don't get woorried. The is a secondary water pump that runs coolant thru your engine after shut off. It located under your intake manifold, and is most likely leaking a small amount. Look for a pinkish crust forming behind the F-hoes area under the intake. The other one may be your leaking coolant at the turbos, fore they"re both water/oil cooled. The "crush washer" gasget on the underside of the turbo may need replacing.

-Mike