The reason for the question is this:

1. If I screw the idle airscrew all the way in, with the IACV disconnected, rpm is about 720.
When IACV is reconnected and ECU reset, idle speed is still 720rpm

2. If idle screw is out abouttwo turns, with IACV disconnected, idle is about 900rpm.
When IACV is reconnected and ECU reset, idle drops to 720rpm

This indicates that when IACV is disconnected air is been allowed into the intake. When it is reconnected it actually reduces air flow. If this is indeed the case then it would be impossible to set base idle via the screw....as per instructions in repair manual. Can someone verify whether the default position of the IACV is "open"? Would appreciate if DS would comment on this

 

the iacv is a device that is opened or closed and is designed to keep the engine rpm at a predetermined value.

if you start the car, warm it up fully until the engine fans run twice, shut the car off, disconnect the iacv and start the car(you may need to feather the throttle to stabalize the idle) the idle should be 550rpm +/-50rpm with no loads(a/c, blower, fans, radio, etc). if it's not there is a leak somewhere, either the fast idle valve or the iacv itself, possibly throttle body gasket or intake manifold gasket ormisadjusted throttle cable/throttle plate carboned up.

with the black intake tubing removed you should find two ports in the throttle body. the lower port leads to the fast idle valve. is there any suction at all with the engine fully warmed up and running from that port(fast idle valve port)? is there any suction from the upper port with iacv disconnected(iacv port)?

 

Thanks for the response, I have an abundance of respect for your knowledge. I did precisely what you described and the idle speed was around 900rpm...idle screw two turns out....fully in, idle is 720rpm. Regardless of either position, once iacv is reconnected, idle stabilises at around 720rpm. It would seem to me that if a leak was present then it would be very difficult, if not impossible for the iacv to stabilise at 720rpm.

It would seem that, when disconnected, the iacv is open and only begin to close when reconnected. Iam going to try your suggestion of testing for suction when the iacv is disconnected. Another reason for posing the question is because I read in another forum that base idle should be set at 1000rpm, with the iacv disconnected, and that once reconnected idle would drop to 770rpm +/- 50rpm. This seems to be what my car is doing. I know this is very different from what the manual stipulates. Could it be something unique to my engine type?

 

no, that engines base idle speed is 550 rpm +/- 50rpm.

in your case there appears to be a very minor leak since you cannot achieve base idle. it can be in any of those items listed above. it can be a coolant problem since the fast idle valve only closes if the coolant temperature raises. if the coolant is low the correct coolant temp will not reach the fast idle valve.

since you closed the base idle screw and disconnected the iacv, air is entering the engine somehow - a leak. a leak is described as anything such as a carboned up iacv leaking, throttle plate gummed up causing a leak, throttle stop screw misadjusted causing a leak, fast idle valve leaking when fully warmed up, intake manifold cracked, or intake manifold gasket cracked causing a leak, throttle body gasket leaking, etc. a very small leak can be compensated for by use of the iacv. perhaps the valve cannot close completely for some reason or another?

are you experiencing any problems in the first place? have you tried a throttle cleaning?

 

OK...I disconnected the iacv, closed the idle screw and checked for suction at iacv and fitv ports...absolutely no suction. I placed my hand over the TB mouth and it was almost sucked in!!...of course the engine died. Adjusted the valve plate stop screw and now all is well!! Truth be told, I had suspected the valve all along but it is always reassuring to talk with a real expert. Once again, many thanks for your valuable advice

 

Some misguided mechanicmust have messed with the throttle plate stop screw. That is not supposed to hold the throttle open. Only just enough to prevent it from wedging stuck closed.