MB4 ESI Auto-Manual swap IACV issues

[UKDMgarage]

Hi all,

Manual swapped my D16w4 ES VTEC MB4 recently 

I have a supalite flywheel fitted , however the engine spins down slowly, and when driving there is very little engine braking (akin to the throttle being partly open)

I think I’ve narrowed the fault down to the 3 wire IACV setup

Has anyone had this issue? And how have they resolved it?

[UKDMgarage]

^Also having over miscellaneous ECU such as the car feeling like it’s leaning out and pulling timing at 2500-400rpm

[dr_broon]

Not sure on that one, but isn't less engine braking a feature of a lighter flywheel? 

[SirPaperbag]

A faulty vaccum line or a bad IACV could very well be the reason for all of your problems.

Bad vacuum line / IACV -> more air gets into the engine -> lean mixture

That explains the slow rev-downs because the extra air works like a stuck throttle and also explains the timing being pulled in higher RPMs due to a lean mixture.

 

Your engine is definitely being fed too much air, and it has to get in there somehow. Now the fun begins - searching for a leak.

I'd recommend checking your intake system with (low pressure) pressured air and soapy water that nicely foams up where the air leaks out of your system.

 

I don't envy you, searching for mechanical gremlins is always a s**tty job. Especially on modified cars.

Start in the obvious areas, the easiest explanation is often the correct one. And check your gaskets, too!

 

Good luck brother

[UKDMgarage]

17 hours ago, dr_broon said:

Not sure on that one, but isn't less engine braking a feature of a lighter flywheel? 
 

should by theory spin down quicker when static revved in neutral due to less inertia on the crank, not 100% sure when it’s in motion

[UKDMgarage]

16 hours ago, SirPaperbag said:

A faulty vaccum line or a bad IACV could very well be the reason for all of your problems.

Bad vacuum line / IACV -> more air gets into the engine -> lean mixture

That explains the slow rev-downs because the extra air works like a stuck throttle and also explains the timing being pulled in higher RPMs due to a lean mixture.

 

Your engine is definitely being fed too much air, and it has to get in there somehow. Now the fun begins - searching for a leak.

I'd recommend checking your intake system with (low pressure) pressured air and soapy water that nicely foams up where the air leaks out of your system.

 

I don't envy you, searching for mechanical gremlins is always a s**tty job. Especially on modified cars.

Start in the obvious areas, the easiest explanation is often the correct one. And check your gaskets, too!

 

Good luck brother

Cheers dude!

Checked for vac leaks already and none have came up, used soapy water, as well as the old brake cleaner technique

Definitely reckon it’s throttle body related, will dive into it this weekend 

[dr_broon]

19 hours ago, UKDMgarage said:

On 10/22/2024 at 6:47 PM, dr_broon said:

Not sure on that one, but isn't less engine braking a feature of a lighter flywheel? 
 

should by theory spin down quicker when static revved in neutral due to less inertia on the crank, not 100% sure when it’s in motion

Yeah, I must admit I'm not sure. You're right it'll lose revs quicker, but it feels like the momentum of the car will drive the engine easier as well. Can't quite get my head around it. I'm sure when I was looking into them before I got my ITR one that was one of the supposed downsides (along with losing grunt uphill), but it's a long time ago now.