My misfire issue is still not resolved

I've been dealing with this for quite a while with my s5 t2



Symptoms?

1. Misfire when revving in neutral above 1k (not backfire, just misfire)

2. Misfire upon decelleration when revving in neutral (series of popping sounds)

3. Rough idle upon warm restart on a hot day (i imagine due to heat soak), goes away after 10 seconds of driving.

4. Low vacuum upon warm restart/hot day. (14 in/hg as opposed to 17-19 in/hg normally) Although the AFM reading on the AFC shows more flow than normal idle.

5. Intermittent loud buzzing sound from the ACV. Seems to be related to misfiring, but i can't figure out how.



What have i done?

1. Set the TPS 104132519073590813906908136 times

2. Pulled the BAC off and tested it, works flawlessly, and is clean as a whistle.

3. AFM is not sticking.

4. Replaced vacuum lines around acv, all except the bottom one which i couldnt reach.

5. Checked throttle cable for stickyness/adjusted.

6. Checked dashpot

7. Re-did grounds (two VERY good grounds, in addition to the stock grounds)

8. Checked vacuum leaks as best as i could using propane and water.





Oh by the way, the issue diminishes when the A/C is on (BAC giving the engine more air).





Suspects?

A) Injectors

B) ACV diaphragm busted



No backfires when shifting, shitty MPG.



I just bought a new ACV ... the current one is buzzing so i dunno if that's the problem or not. Perhaps there's an internal vacuum leak.



The issue is nonexistant for the first 30 seconds of the car's startup. Meaning, no misfire, just runs/idles like a dream!!!



Then all of a sudden, the idle goes up about 200rpm, and stays steady, but starts misfiring/smelling rich. At 750RPM, there are no misfires. As well with the A/C on, there are no misfires, no matter what rpm.



WTF could it be? on cold startups, what the fack runs for the first 30 seconds and then stops? What could this POSSIBLY be?



Thanks!

-Ross

That is strange, I know the acv plays a role in misfires though. Get that swapped out and let us know.

but it's such a BITCH to reach... especially with ABS :(

Why do you still have all that crap? Even if you have to live with emissions, get rid of that abs, i bet yours leaks...

Nah it's brand new https://www.nopistons.com/forums/pub...DIR



I hate it but i'll keep it ... stops me faster.

all those symptoms are pretty normal for s5's, and rotaries in general. they like to misfire with no load, its kinda how it is. the poor running for 30 seconds after a hot start might be the fuel pressure regulator or the solenoid, the ecu bumps the fuel pressure to advoid vapor lock



mike

https://www.nopistons.com/forums/pub...1047683591.gif right on mike, i'd say it is the FPR



nick

FPR eh? how do i test it? or the solenoid for that matter?

You could try bypassing the solenoid all together and running a vacuum line right from the FPR to the dynamic chamber to find out if the solenoid is bad. There should be 3 vacuum lines going into your DC from the rats nest solenoids. Trace the one that goes to the orange solenoid.. that is the one for the FPR. I think if its the solenoid, the ECU would throw a code though.

i think its easier to blame it on the injectors