Help diagnosing intermittent power loss

[Sims]

Hello from New Zealand.

I'm currently 5000kms in from a complete ground up rebuild of my 2.3l, and now its having new problems.

While cruising on the highway in 5th, i noticed a slight loss of power - similar to the AC coming on. When pressing the accelerator to maintain speed, the engine felt labored and bogged, making a loud induction noise but almost no power. The engine still sounds in balance - e.g it doesn't feel like a misfire - more that its starved of oxygen perhaps. Closest analogy i can think of, is its kinda like starting a 2 stroke, but shutting the choke off too soon. You try and give it some gas, but it just struggles to rev.

If i cruise to a stop it'll happily idle and everything returns to normal. My girl friend has confirmed that this has happened to her also.

The injectors have been cleaned reasonably recently, and I've cleaned the MAF sensor also. Next step would be to pull the EGR valve and clean that. Last on my list would be replacing the PCV valve.

After that, I'm at a loss.
Any words of wisdom folks?

 

[slow 3]

Do you have a intake on it by any chance?

 

[Sims]

My mechanic is a legend - Correctly diagnosed the problem as a worn/lose catalytic converter core, from the slightest exhaust rattle on cold start-up. The core moves around and leans against the O2 sensor heating it up. Thus causing a malfunction in terms of how the ecu/pcm reads the air/fuel mixture.

As there's no emissions testing here in NZ, we just bashed out both cats - Problem solved and the car has a little more top end

 

[slow 3]

Wow, I would keep him around for a while if he figured that out lol. Glad to hear everything is working then.