turns out the IAC was new as well, was changed with the TPS when the engine was rebuilt, they are both in perfect condition. i thought the IAC was not ned because of how it looked from the outside, but once detached from the TB, i saw it was brand new.

bumblebeast8892, i saw the fins you are talking about

 

Make sure you have adequate, and stable fuel pressure

 

check the wiring in your maf harness. my 99 GST had a problem very similar. it took forever for me to find it. do you have a wideband o2? if so, what is it reading when the car starts to run poorly?

 

also check your cam angle sensor and maf.

 

check the maf harness in what way?
i dont have a wideband installed, but you can smell the unburnt gas coming out the exhaust


and nothing is wrong with the maf sensor itself, as mentioned in the first post, i tried one from another evo 4.

fuel pressure is also good, have bigger fuel lines and stuff, so it's not like there is restricted flow

 

If you've tried more than one MAF, it has to be some type of tuning related issue. I'm not sure if the tuners in Trinidad have began to use Speed Density yet rather than MAF.

 

down here we still use MAFs. some guys eliminate the MAF though when using certain managment systems.

now the thing is, this is happening with the stock ecu, i have not tried another ecu as yet (no time to get one). will be trying to get one this weekend to swap out and see