as you are accelerating hard and it goes flat ...if you back off can you feel it sort of jump back to "normal" or does the fault remain right back until idle ? if it does jump as you back off then look at the high tension system supplying the spark plugs it sounds to me like there is a breakdown of the insulation somewhere this is often evidenced by burn marks on the sections around the plugs or white powdery tacks

on the 2TZ-FE MODEL with a distributor pay close attention inside it and in particular the rotor which can break down through the centre

more likely leads you probably have one gone and another folowing but always use insulated tools as a shock off this side of the system can be fatal

I have read the problems you are having with the Previa. From what you have described the problem to be, the following, in the order listed, is what I would do/check initially:

1) I would replace all ignition components. I have found this to be good practice on vehicles of that age and vehicles that run the old distributor and rotor arm systems.

This would include:

Spark plugs (NGK) - HT Leads - Distributor Cap - Rotor arm

2) Check for any air/vacuum leaks/blockage around the air intake and throttle body. Also check the exhaust system for blockage/leaks.

3) Make sure the throttle valve is not sticking or damaged. Check linkage and cable too.

4) Using a scope, check the input/output signal at the idle control valve.

5) Check the fuel system for a good healthy flow rate and pressure. Check the fuel pressure regulator.

6) Using a four channel scope, measure the signals at the injectors.

Hope this is useful or at least you know what needs to be checked: you can pass this info to your local garage to have them test what is listed.

Good luck

Edited by Avant on 24/08/2010 at 23:12