Car is VW Golf MK4 1998 1.6sr AKL engine, fitted with LPG.
I'm looking for a solution for a problem that I've been trying to fix for the last couple of months.
The problem I'm experiencing is this: the car starts really easily in the morning, goes immediately up to 1100-1200rpm (I think this is normal when the engine is cold), but after 5-6 seconds, the RPMs start going down pretty fast, the engine is misfiring like crazy, and it just starts sputtering in the 300-800RPM range. There is a very strong petrol smell from the exhaust. If i press on the gas, the misfiring stops at the higher RPM's but the RPM's go reeeaaallyy slowly up and down (even if I just blip the throttle a bit, the rpm's will surge up to 2000 very slowly, and slowly come back down). As the car warms up the problem gets better almost linearly. As soon as the car automatically shifts to LPG, it's running great and idles great, except for a small flat spot when pressing the gas. When the car gets up warmed up, it's working really well.
I've scanned it with VAG-COM, and I got a 00537 - Lambda Regulation: Lower limit. Even when the engine is warm, if I let it idle i can see the lambda regulation values slowly go up to minus -25%, but if i blip the throttle the value goes up to 0% instantly.
So far, I've changed the O2 sensor, coolant temperature sensor, the fuel pressure regulator, cleaned the throttle body and adapted it, cleaned the MAF (and tried with one from another AKL golf), used a fuel cleaning additive, PCV breather valve, N80 valve, and the plastic hose that goes from the MAF to the throttle body. I just can't seem to fix this thing.
I haven't checked the spark plugs since it works great on LPG, but I'm not sure about anything anymore. Any help is appreciated.