S4 NA Idle and stall issue
 

So I just put on a K&N cone filter to my MAF with an adapter, and removed the air pump, installing a double pulley on the alternator. I have plugged the AVC inlet (block off plate is on the way), and capped the EGR valve and it's vacumn line to the solenoid. I also removed the fan cowl to do the belts, and am looking at doing an electric fan installation shortly.

The car will start up just fine, and idle nice and smooth most of the time. However once in awhile, when coasting to a stop, the car will stall out or idle very roughly. It will sometimes stay alive when the car comes to a halt, but will idle very low (around 300-500). If I give it more gas, it will run smoothly again, but if I take it back off the gas it will go back to rough idle.

I was wondering if this is fuel/air issue or if there is something else going on here. Do I need to adjust the idle to compensate for the extra air the new filter is getting? Did I create a vacuum leak somewhere?

First off, there is probably not any extra air getting in there (especially at idle). The engine pulls air in, it doesn't get pushed in. The K&N air filter and other cone type filters are designed to be used in an effort to get colder air temp into them, not MORE air. Therefore, if you have the cone filter in teh stock location without anything else done to get to colder air, it may actually be worse than stock. The stock filter is not bad actually.

Second, you most likely have a vacuum leak (imho). Check to make sure all of your hoses are connected or capped off.

Third, is your MAF in roughly the same orientation it was before? The S4 AFM (MAF) do not like to be in any orientation other than level. The "door" can act strangely if it is not in the stock orientation.

Rob R.

If I did create a vacuum leak, I don't know where it would be. I checked all of my hoses and connections and everything looks good there. Could the ACV be causing this?

My MAF is in roughly the same orientation. It may be tilted to the side slightly and higher up. It is temporarily mounted, with a box on the way. I will look into making it closer to stock.

Thanks for the help!

Intermittent problems can be tough to find. You can spray WD-40 around the intake while its running rough. But u said it only does it once and a while so good luck.

I would kick up the idle and calibrate the TPS.

Just a thought... Did you mess with the variable resistor right on the passenger side shock tower? If so, that might need adjusted.

I would not adjust the idle on the throttle body unless you messed with it. Nothing you did should effect idle. (unless there is something not plugged in correctly or something is open.

Rob R.

I took another look and noticed that the EGR was not capped properly. Seems to be just fine now! Thanks for the help

Would that be considered a vacuum leak? I thought vac leaks cause high idles? I kind of have the same low idle in my 86 n/a, just around 500 rpm after a 5-10 mile drive (haven't gone much further), but was thinking its more of an electrical load or tps problem???

AFM based systems like the stock FC will usually idle low and choppy in the presence of a vacuum leak. being that the afm reacts to the amount of air drawn through it ANY air leak beyond the AFM will cause a lean condition on non turbo engines, on turbo engines it will result in a lean condition out of boost and a rich condition while in boost(unless the leak is in the turbo intake duct, then it will always be a lean condition).

Just fyi, removing the air pump is eventually goin to cause your cat to clog up, if you have one

Thank you for the detailed response! It is appreciated