VS surging underload, sometimes.

[streetholden]

Hey guys, i have a BIG problem. I have searched these forums for a fix and no luck.

Its a VS ecotec and it surges. To give you an idea, tonight, as cold as it is i went for a drive, giving it a bootful everywhere to show a mate. The trip there was 5km, not a problem, on the way back, right throughout the gears it would bog right down and surge.

For the life of me i can not figure it out, i was told fuel filter, done that. Then told oxy sensor, done that, coils, leads and plugs, done that. Its an ecotec with a 12mm manifold insulator and plenum spacer. Any ideas on what it could be?

Cheers guys, if you need any more info just ask cause i dont know how else to explain it but i can take it out again and try your suggestions.

[streetholden]

I had been told to check the error codes, and got the all ok. Much difference checking it using the paperclip trick or using a tech2? I also forgot to mention it only surges underload. Slip it into neutral and itll rev freely all day every day.

Also i dont know if its any help, but you need to winded the engine over for roughly 5 to 10secs for the first start of the day or if its been sitting for say 4 hours or so.

[304runner]

Mem cal maybe?

[streetholden]

Its still the stock memcal, this surging has progressively getting worse, its making me think maybe the transmission, i just had a poke round the engine bay checking if everything is pluged in, sealed and so on. I dear say if it was the memcal, it would do it al the time, not when warm. Cold seems to be alright.