99 3.5 swapped automatic, VB mod, high stall converter, Nismo R-tune knockoff cams, HR springs, ARP rod bolts, SSIM, and bolt-ons.
This is the swap using 3.0 timing stuff and 3.5 tb. FPR reads ~41PSI at idle.
Pulled codes and its all emissions stuff most of which are not connected anyway.

On to the issues:
1. When coasting on the highway going about 120km/h, if I take my foot off the gas and then try and feather the gas pedal again, there's no response. I will have to keep pressing little by little and then all of a sudden the car will jerk back to life. This only happens in 4th and lock-up. The severity of the jerk decreases as the speed increases. It may be the VB mod but I never had this problem with the 3.0. Lock-up doesnt happen unless i'm up to speed (65km/h or higher) and I rev the engine to 3k rpm. Then it will lock-up. If I dont rev to 3k or higher, lock-up will not happen.(For some reason I'm leaning towards TPS)

2. Once in a blue moon when I'm driving on the highway, if I go to pass someone and I give it gas, it feels like I hit a rev limit or some kind of fuel cut. It happens at random rpms. The throttle will become non responsive, engine will not rev and I will have to take my foot off the gas and then reapply again and that's when it responds again.

3. Rough/lopey idle (expected somewhat), and backfiring and hesitation up to 2k rpm. Feels like it has less power than the 3.0 from up to 3k rpm and then comes alive from 4k on. I'm guessing it's the overlap from the cams and the fact that the car is running rich (getting horrible gas mileage). Not so much a major concern right now because I will be tuning soon.

Before I go poking around, I just wanted to get an idea of what others might think based on my description of the problems.

 

Probably tuning is a large part of your problem. Pig rich from larger injectors, more fuel pressure, combined with the overlap, plus your throttle tip-in enrichment will probably be putting you momentarily in the 9's AFR or below...

 

Mine reads about 41psi, but at WOT.
At idle it fall between 30 to 34.

 

I'm using a 99 california spec ecu in my 99 fed spec. Old ECU burned out. I'm getting a code for rear heated o2 sensor. (P0161) This is a cali spec code but I was wondering if this can cause any issues.

 

I was on my way to work today and the fuel cut thing happened again. But this time its consistent and the car will not rev over 2700rpm. I need a new MAF.

 

I hope that it will solve your problems.

 

Ah yes that could definitely explain it also.

 

quick question, my dek swapped i30 also does the "fuel cut" thing around 3k rpm. Could it also be the MAF? When it happens i turn my car off and restart it and it revs fine all the way to redline.

 

I tested the old MAF and it is within spec. I picked another one up at a junkyard and put it on and checked the specs and it's the same as the old one. The car behaves the same. I will reground the MAF harness when it stops raining.

The weird thing is, last night after I shut the car off and started it up again, i took it on the highway and i was able to go above 3500 rpm. Now I'm second guessing the MAF thing. (although the intermittent problem could be a MAF on its way out but not quite dead) Is there anything else besides the MAF that could limit the revs to around 2700?