Start Up RPMs (1 Viewer)

[landtoy80]

I took apart the IAC and it was no carbon and the shaft moves smothly.

Before I add the O-ring(s) what else should I look for?
I don't want to cover up one porblem by modifing another part (the O-ring IAC mod).

Why would the startup idle be fine for years and now rev up to 2000 rpm?
If the IAC still opens and closes like it should when it was new, what would cause it to chang now? It lets the same amount of air in as it did when new.

This is a common problem on the 1FZ as there is a fix for it http://www.safari4x4.com.au/80scool/tech/fast_idle/fast_idle.html

What milage does this problem start at?

There has to be a reason for why it all the sudden starts to rev high.

Could it have anything to do with the black flat washer spring thats in the IAC that goes on the end of the shaft? Could that spring be weak? Does that spring keep the shaft from opening to far? Has amyone tried to adjust that spring?

 

[MoJ]

I don't want to cover up one porblem by modifing another part (the O-ring IAC mod).

Why would the startup idle be fine for years and now rev up to 2000 rpm?
If the IAC still opens and closes like it should when it was new, what would cause it to chang now? It lets the same amount of air in as it did when new.

Kurt - I completely agree - it seems like this O-ring mod is just covering up the symptoms instead of addressing the root cause. Has anyone tried replacing it instead of modifying it? I'm sure these trucks didnt do the start up rattle when they were new so why now? Not sure I've ever read where someone answered that question.

 

[landtoy80]

Could there be some wear in the IAC or in the throttle body?
From the pic in the FSM it looks like the IAC just moves back and forth opening and closing the port. At startup the port is open (cold) it lets more air in thus increasing the RPM's. When the motor warms up, the port closes thus reducing the air flow ,decreasing the RPM's
Adding the O-rings will make the opening smaller, letting less air flow, lower startup RPM's. So I don't think a worn IAC would cause the higher unless the metal is wearing where the valve seats. THis would let more air flow, increasing the RPM's

One thing that could cause more air to flow would be a worn or obstructed throttle valve.

I still would like to know what milage does this problem start at?

 

[semlin]

i have not taken an IAC apart but if there is a spring in there somehow regulating air flow it could be sensitive to temperature or fatigue, or there might even be a problem with the original manufacturing standard. Maybe I'll try cleaning the thing.

 

[MoJ]

One thing that could cause more air to flow would be a worn or obstructed throttle valve.

Are you referring to what many of us mistakenly call a "butterfly" valve? If so, mine is clean as a whistle and closing as it should. But cleaning it had no impact on the high rpm start for me. It did however completely cure the low idle problems I was having.


If I had a new and used spring to compare, I have ready access to a spring rate compression gage. It measures the amount of force required to collapse a spring various distances. From working in an industry that makes springs I know as a fact that every spring takes a set and loses resistance overtime. I was wondering if anyone replaced it rather than O-ring'd it. If so, any improvement in the high rpm start? I may be beating this one around too much but believe there's a better root-cause fix than just putting a couple o-rings around it.

 

[Cpt. Kirk]

high idle at start as well

I've owned the vehicle now for 4 years and I thought the high idle was just the nature of the beast but it always concerned me to hear it rev so high when it is cold. Now I know better, the o ring solution link to safari 4x4 isn't working could somebody explain the trick to installing the o rings.
thanks
93 cruiser 70 000 miles