For those who dont know, you probably can't help

Its part of the system that makes a car into what I call fat beurocrat mode, removing most control of the engine from the driver - it slows the rate of throttle closure to prevent driveline clunk when you snap the throttle closed. Along with the torque converter clutch mod to make the car drive less like a hunk of s**t, I want some engine braking. A 4 litre motor with 9:1 compression should provide s**t of engine braking but this tends to provide less than a 2 litre motor of similar compression....

Anyone know how to fix/improve this?

Well im guessing yours is an auto, in which case its the transmission freewheeling (well not freewheeling, but coasting) thats not causing the back pressure. The motor itself should provide plenty. If you drop the auto back a gear, it brakes a bit more

Or

Do what I did and unbolt the ISC and replace the gasket with a home made gasket, made from two layers of cereal box cardboard, that has no air flow holes in it.

I just set the Base Idle speed screw manually to what I needed. I set it to idle at 750rpm in drive when the enigne is hot.

My car starts and runs fine, sumer and winter. But, I now have more engine braking when driving through hilly areas.

Epitome, tell me more about the ISC, does the ECU keep it open wider when the revs are above idle?

Andrew, I am kicking the auto down a few gears, my old car with a nissan rb25det motor has the same compression and 1.5 litres less capacity and it provided much more engine braking. I'd also imagine it had a considerably wilder cam profile, being a performance engine unlike the 4 litre in the taxi. Having a milder cam profile will increase the dynamic compression so it theoretically should provide much more engine braking.....

Yes it does. To reduce emmissions when you lift off the throttle going down hill.

The ISC sits on top of the Throttle body.

Cheers for the reply.

Will do further investigation into the ISC behaviour and how to improve it to make me a driver, not a passenger.

One thought, all EFI vehicles I've worked on to date completely cut fuel when the throttle is closed and revs above a certain amount, typically 1500-2500rpm. Hence the throttle dashpot function would have no effect on emissions, only on trying to smooth out the driveline....