strangest problem ever. (moving posts.)

[DDRaptor]

This is a copy paste from daewooclubuk where I originally posted this before i found this place.

Hello All,

So I have a Nubira with a Lanos 1.5L SOHC A15SMS Engine.

Car has been champ since i got it, just small things here and there. Always lost almost all it's power on steep hills. So I got the basics Plugs, Plug wires, Air filter etc, oil and filter change. Problem mostly disappears, I guess the extra air through my short ram intake helped a whole lot.

Anyways It started to lose power on flat land under constant throttle, I thought it was running overly rich/lean so i put a new 02 sensor that did'nt help much, The problem stay and has gotten so bad it idles lumpy and stalls at times.

Current situation:
sitting still: pressing gas to any rpm and holding for about 3-5 sec and then RPM drops with no change in throttle position.
driving: will be driving at any speed and suddenly lose power.

Both issues are resolved as soon as I back off the gas and apply slowly again.

What I have checked.
Plugs (still firing while holding throttle steady and engine stumbles)
Injectors (still energizes while holding throttle steady and engine stumbles)
TPS (Voltage holds steady while engine is stumbling)
MAP (thought this was the problem and replaced it unnecessarily)
EGR Valve (Removed and checked it perfect shape)
All Vacuum lines (double and triple checked)
Fuel Pressure (steady at 41psi idle and 50 psi with throttle)
IAC (idle air control valve - removed and cleaned)
Compression test - all cylinders achieve 120psi within two revolutions
*Heard a strange slap sound when doing compression test could not figure out where it came from but all cylinders were even
O2 Sensor (checked for voltage with engine idling.

Starting to think either I suck at my job or It's something more internal weak valve springs or even a clogged cat converter.

Would love to hear opinions it's been 2 weeks and i have nothing to show for it.

***Forgot also vehicle has no codes. Only Does this at operating temp.

At first I did'nt think cat/exhaust because it only happen after a few seconds but now I am open to check anything.

thanks guys.

added a video so everyone understand what i mean.
http://www.flickr.com/photos/23462874@N04/5156914222/

This with no change in gas pedal position.

UPdate.

It started getting colder and dipping below freezing overnight. And the problem disappeared dont know why but i guess it has to be exhaust because engine always reaches op. temp. Guess thats a problem solved till spring which lets me get creative with exhaust bits.

***Update again It has taken a real bad turn. I have a steady knock now only in gear under any load light/or heavy. I never use half throttle speed limits are only 80-100kph. But I am seriously worried about the engine losing a crank bearing. I have no idea why this is happening. I am due for an oil change been around 6 months. Hopefully that will fix it. But I think is a sensor somewhere that I have not checked.

[DDRaptor]

I have reconnected the EGR Hose and the knock went away but the original problem returned. So. I don't know what to do run with the EGR and knock lightly all the time or run with it and run super rich and mess up all my spark plugs, I don't have a vacuum gauge or pump to which test it with.

[DDRaptor]

I think I might have found the real cause of this problem. Today I drove about 25km in the morning to work at a different location with the EGR valve disconnected there was slight knock as to be expected. But in the afternoon on the way back I reconnected the egr valve I noticed that there was smoke leaking from the egr gasket. I Believe that the gasket is leaking and I am wondering what kind of sealant I could use. I have the Lanos service manual covering the a15sms engine but I have not looked up this issue yet.