92 JDM FD3S - Bucking - low rpm, warm. No second boost.
 

Firstly I'd like to say I did post in new member technicals, but it seems to have vanished. Secondly, I have searched long and hard around the internet and have gathered what I think may cause the problems, but I'm new to these cars, I've just bought it and I don't want to bugger up my new pride and joy.

Specs: JDM 92 Type R, only mods being a decat and 4inch back box done by previous owner. No map, hence I'm now not driving it until I buy a Cat or a PFC.

1st problem: severe bucking at RPMs under 3k, ONLY when warmed up, and ONLY when apply a small amount of throttle (i.e. trying to cruise). Getting the anchor down just slightly further (and up to full throttle), the turbo spools and the car takes off like a scalded cat. I can also drive the car smooth as silk provided I keep the RPM above about 3.5k. Idles perfect 800. From being a keyboard warrior, I've narrowed this down to grounds, TPS, O2 sensor or a gypsy curse.

2nd problem: No 2nd turbo boost. 1sr turbo pulls hard as nails, when 4.5k comes it falls flat on its face and it's a slow creep to the redline (I give up by 5k). Keyboard warrior initiative says solenoid or vacuum. No smoke or anything.

What are your thoughts? Thanks in advance.

Okay, well for reference I got rid of the hesitation by putting a custom ground from the grounding point near the sparks to just under the fuse box.