blo94s4

hi everyone need some advice. my 94 s4 is missing. it will idle fine for 20 seconds then bog down miss. while driving it will miss bad when cold and some when warm especially under boost it misses bad from 3 to 4 thousand rpms then seems to clear up a bit. i did ls2 coil kit from mr. swanson, changed spark plugs, checked the injectors, new fuel filter, put on a stromung and the car still misses. the guy i bought the car from had to replace the fuel pump at 80,000. i bought the car with 87,000 and now the car has 137,000. i think the last step is the fuel pump. if i buy the 044 bosch pump will it fit or do i need to get other hardware to make it fit. sorry for the long post. thanks for the input

UrS4boy

Check your Mass Air Flow (MAF) sensor. It might be dirty (clean with an isopropyl alcohol bath) or the connection might be dirty or not all the connector pins are fully engaged (push the individual harness pins towards the male MAF pins (while the connector is engaged - peel back the harness boot).

Likewise, it could be the throttle position switch (similar issues) or the O2 sensor (dirty).

blo94s4

i checked out the connecting pins on the maf and they looked good(no corrosion. idisconnected the plug on the maf started it and drove about two miles the car ran the same with the plug off as it did on.i dont know how to clean the maf. just submerge the whole unit in alcohol? also the car seemed to run worse when i put the new spark plugs in. i forgot to mention that sometimes the car cranks over alot before starting sometimes fires right up. thanks again

sk88erguy

When was your O2 sensor last replaced? it can cause hesitation and idle stumble (i know)

blo94s4

as far as i know its original. i looked at it when i put on the exhaust and it looked good if looks matter. i was careful not to touch the end. wouldnt that stuff turn on the check engine light if they were out. like o2 sensor, throttle pos sensor?

sk88erguy

Mine was original too, i have 120K, they are 60K mile replacement interval for the o2 sensor. mine was very very black with soot on it but i had been running slightly rich because of a bad coil as well.

I replaced the coil but still had idle stumble, i had no engine codes at all, replaced my O2 sensor and all symptoms went away. car runs like new.

So to answer your question no, it doesn't always throw a code. mine was as dead as a door nail and never threw one. I got mine for 50 bucks at autohausaz.com i believe. i got the s6 sensor 13957 it is plug and play, just a little longer cord than the original.

If you haven't replaced yours in the last 50K miles, id do it. even if it isn't your problem now, it will be. its a good thing to try if you have no ignition problems (since your coils are new)

blo94s4

thanks for the input going to order one. what is a wideband o2 sensor?

sk88erguy

Wideband zirconia sensor

A variation on the zirconia sensor, called the "wideband" sensor, was introduced by Robert Bosch in 1994 but is (as of 2006) used in only a few vehicles. It is based on a planar zirconia element, but also incorporates an electrochemical gas pump. An electronic circuit containing a feedback loop controls the gas pump current to keep the output of the electrochemical cell constant, so that the pump current directly indicates the oxygen content of the exhaust gas. This sensor eliminates the lean-rich cycling inherent in narrow-band sensors, allowing the control unit to adjust the fuel delivery and ignition timing of the engine much more rapidly. In the automotive industry this sensor is also called a UEGO (for Universal Exhaust Gas Oxygen) sensor. UEGO sensors are also commonly used in aftermarket dyno tuning and high-performance driver air-fuel display equipment. The wideband zirconia sensor is used in stratified fuel injection systems, and can now also be used in diesel engines to satisfy the forthcoming EURO and ULEV emission limits.

Wideband sensors have three elements:

* Ion Oxygen pump
* Narrowband zirconia sensor
* Heating element

The wiring diagram for the wideband sensor typically has 6 wires:

* resistive heating element (2 wires)
* sensor
* pump
* calibration resisitor
* common

I got that off wiki. All i know is you shouldn't mess with splicing one in there (a universal) because there have been discussions on this forum about those universal sensors not getting the same gas mileage and performing worse than the standard one. Just buy the 13957 anything else is asking for trouble.

blo94s4

installed o2 sensor and made a world of difference. still some hesitation in 3500 to 4000 rpm range but i can handle it. my old o2 was a bright white color. thanks again guys

sk88erguy

Glad to hear it helped out. i hope you can find the other problem as i know how frustrating hesitation is...

My o2 was so black, ive heard people say theirs was white and i think thats more normal.