Car is a '91 GTI 8V with Digifant 1 (California spec).
Yesterday it started running really crappy on me with not much warning.
Started with misfiring at idle. Then under load it was stumbling a bit (city driving) and still misfiring.
Car seemed to run better once on the freeway at higher speeds, but in city traffic it gets pretty cranky. Will eventually stall at idle if I don't keep my foot on the gas to about 2000 rpm.
I then noticed that, at idle w/foot on gas, that it smelled rich. Not sure if it really was rich or if it was just because i had my foot on the gas to keep it from stalling.
Got it home, let it sit overnight, and looked at it again tonight. With the engine cold it'll run, but it still idles bad and wants to stall, especially if I rev it and when the revs drop, they often drop to nearly zero. It smells rich...granted it's a cold engine, but it smells even more rich than I'm used to.
Pulled the plugs and cleaned them. Kinda fouled and a little wet. Smelled like gas (is this normal for them to actually smell like gas?). Reinstalled them, started car, still runs like crap.
Now I experiment. I pull the fuel pump fuse and as soon as I do, the car runs smooth/normal for about 5 seconds then dies.
So now I'm thinking that the car is probably flooding since it ran much smoother with the fuel pump fuse pulled...so I'm thinking that in that interim time between the pump first shutting off (when I pull the fuse) and when it dies, I'm thinking it's burning off that extra fuel that might be flooding it and in that 5 seconds or so it's no longer in a flooded state.
And I'm getting no CELs either (I have a CEL on the dash) and I checked for fault codes and got none.
I also disconnected the O2 sensor (engine still cold) and no difference (and no CEL...shouldn't the CEL be triggered? I thought that was odd that I didn't get one with a disconnected O2 sensor).
I do have a (used) O2 sensor that I could swap in just for fun, but assuming that isn't the problem, I'm thinking the fuel pressure regulator is bad and it's flooding the engine. Sound logical?
The other thing to know is that the infamous transfer pump was replaced within the past 2 years (I forget exactly but it's not really old) and the car shows no signs of fuel starvation either. When it's not misfiring the power is just fine and at freeway speeds it runs pretty good and I have no problem accelerating. It's at lighter or no-load that it acts up. I also just for fun swapped out the fuel pump relay from my Eurovan (same relay) and it made no difference.
So assuming the O2 sensor isn't the problem (I'll swap it tomorrow night or this weekend), would the fuel pressure regulator be the next logical item to change? They're not horribly expensive (about $80 I think) but not cheap either. I know there are tests in the bentley for it but I don't have the equipment for testing it out.
I'm also kinda ruling out ignition issues for now because there's no backfiring (usually when I have a misfire due to ignition issues (e.g.: wash the engine and wires are wet) I usually get backfiring too but I don't get backfiring now).
Thanks!