Alright so my friend has a 98 A4 1.8T GIAC chip, ATP TP, Magnaflow Muffler, and an Ebay FMIC. The problem is when he floors his car at low rpms it stutters like crazy and jerks and backfires and boost goes all over the place and making a popping air noise (not a backfire). Checked the IC hoses and for leaks and there are none. If he floors it from 4k rpm he boosts to 21 psi with no problem or stutters. Sometimes when you floor it you also get like 4-5 little back fires in a row. So far we've tried replacing the DV, changing DV springs, new plugs NGK bkr6e w/ .028 gap, n75, MBC, new coil boots, and a new MAF and still have the problem. I also noticed it only occurs when the car boosts more than 15psi before 4k rpm's.

NEW INFO****
while driving tonight he finally got a code for a misfire in cyl 4, i erased it and swaped the coil pack and the cel didnt come back on yet but the car is still misfiring under heavy load when going wot from 4k rpm with loud backfiring that is continous, its just pops and the car is still able to get through the misfire. at low rpm wot the car bucks violently. When i uninstalled his mbc and ran just the N75 it continued to pop as soon as a went wot and continued all the way till redline but the car did not buck at all just backfires. When I put the mbc back in line with the N75 it bucked bad at low rpm wot but not as many backfires up top. Were gonna try running some bkr7e's and see if that solves some of the misfires. right now he has bkr6e's with a .028 im gonna try to regap them should i go with a larger or smaller gap to experiment?

 

It's not the spark plugs causing it but they may now be fouled from misfiring. It is probably the coil or ICM. It is backfiring because the unburned gas from that cylinder or possibly cylinders is burning up in the exhaust.

 

First you said
Then you said
Im a little confused, but I agree with tractioncontrol.... Probably a coil pack problem or ICM.

 

sounds like coil packs

 

yeah we figured it out first off the gap on his plugs were too large .032 and second a bad coilpack on cyl 1 although we kept getting a code for misfire on cyl 4. We put a fresh set of NGK BKR6E plugs gapped at .028 and changed two coilpacks and it runs like a champ

 

Just had the same exact problem. Took it to the dealer and they had to replace 2 coils for the spark plugs

Hope that helps

Dennis

 

it ended up being a combination of plugs and coils