Feeling Those Bad Vibrations

[zak-ery]

Hello! I've been lurking these pages for an explanation to my problem, some info I've read comes close to a solution but not quite there yet.

The car is a '97 Stagea RS4 auto, pretty much stock everything besides an SAFCII which I know nothing about as far as settings it may be running since it was installed by the previous owner. I've owned the car roughly 5000 kms.

Problem: I've been experiencing extremely temperamental engine vibration and hard starts. I can't seem to figure out any absolute constants to the problems so figuring out a diagnosis is difficult.

Symptom 1: to elaborate on "hard starts". When I turn the key the engine jumps arbitrarily between 0 and ~500 rpm while the car shudders and vibrates. If I depress the accelerator all the way to the floor for a split second, the revs are up and the problem is usually negated and I'm up and running, if I do nothing the engine tries to bounce off 0 for a few more seconds before cutting out. What makes this temperamental is occasionally I will turn the key and the engine is up and running with no reluctance whatsoever, often this will be when the engine is still warm, but not always.

Symptom 2: under heavy acceleration there's some pretty horrendous vibration, very noticeable feedback through the steering wheel, and a severe loss of power. Catch: this only happens sometimes, other times quick acceleration is smooth as.

The obvious issue is with ignition, I figured the spark plugs are done for - weak spark causing screwy idle and misfiring under heavy acceleration. I also figured the coils could be ancient and clapped out. I found out which spark plugs I needed and put those in, I also checked my coil packs which turned out to be new enough looking Splitfires.

The results of the new spark plugs are mixed. Starting the car is less problematic although still not really what you'd call smooth. Quick acceleration still achieves the same problems as before, still not every time. There is now also a new thing that happens, but again, not every time. On a few occasions when in drive while stationery and the brakes applied, the car vibrates substantially. If I throw it in neutral, the vibrating stops, and starts again when put back into drive. It's beyond me why the new spark plugs would have this effect given that they are the only variable in this.

If I've left out any pertinent info please let me know. Any helpful insights will be greatly appreciated.

Cheers!

[75coupe]

Perhaps the previous owner didnt know how to use the safc either

[zak-ery]

That's highly likely. I mean I understand what it does, so I see how it could be the problem at play if someone has set it up incorrectly. I can't say I could do any better though.

So I feel inclined to pull the SAFC out and test the car like that. Would you say that's wise or could ripping the thing out upset things?