IAC sucking and high idle fixed

[JBAV6Tony]

Members might recall my S1 V6 manual in my kit car JBA Falcon. I've had many issues over 3 years with the IAC. Some time ago I read articles here. So I renewed the IAC but alas couldn't afford a genuine so ebay was the answer.

Still had issues. So took it out again and as soon as it was lowered down the pintle and spring was loose eg not screwed into the plastic housing. In fact it was wedged in. So it had come loose and was on an angle. Anyways I screwed it on again by not very much say two complete turns. This is because although it adjusts itself it has to strike the top of the peak of the unit to make a seal so it turns off when not needed.

Test drive, get engine nice and warm and still sucks lots and doesn't want to reduce idle speed. Read in this forum of advice to slowly place finger on IAC intake inside throttle body then obtain a 600rpm idle just above rough idle. Idle was still too high - why?. throttle idle screw under sprung throttle plate was jammed. Took plate off and WD40 plus vice grips! and finally it was loose to adjust but the screw had been screwed all the was in eg maximum idle adjustment= high idle. Replaced sprung plate, repeat procedure, idle lowers down to 600rpm. Idle a little rough and some sucking noise, looks like IAC is working trying to keep idle higher. Adjust screw in this time till rpm reaches 700-720 rpm. Sucking vanishes, idle perfect.

Wait for it to cool. Next day start up cold engine. Idle isn't 1300 but 1000rpm. Nice. Wait for 2 minutes it begins to slow down to 700rpm, now sucking from IAC eg pintle is up to the top (extended). Went for a drive. Normally I'd return and idle would be 1300rpm now 700rpm and no sucking. Rev engine high then close throttle, engine quickly falls to 500-550 rpm sucking comes in for 5 seconds, raises idle to 700rpm then sucking stops. If that is how the IAC should perform I'm very happy. All this IAC adjustment stuff and replacement all because some fool screwed in the throttle stop all the way in. That meant the butterfly was always open too far for the IAC to operate as it was meant to.

Thanks to those that made the IAC a topic of discussion. I hope others can benefit.

Here is my caravan I built, recently finished. 16ft x 7ft with full ensuite ATM 998kg. All lightweight, steel tube frame, 4" drop axle, heater aircon etc.
Tony

 

[MikeC]

Thanks for letting us know the final outcome. I guess you now have a spare IAC valve. I'd reinstall the Holden original as I've had high idle problems with the ebay copies after a long hard run.
Nice outfit you've built for touring, by quoting the ATM I assume that you've sorted out any CVM problems with your Falcon tourer.

 

[JBAV6Tony]

Hi Mike

The JBA still has a towing capacity if 850kg. So without carrying water I'm about legal.
We're selling up at Strathbogie and building in Camperdown vic, then I'll get the capacity raised to 1000kg. Be sweet.
Also got a 2.92 diff from a 6 cylinder corty. Replaces the 3.7. Means I can tow in 4th gear. 5th strictly overdrive not far off commodore gearing now
Tony

 

[MikeC]

Hi Mike

The JBA still has a towing capacity if 850kg. So without carrying water I'm about legal.
We're selling up at Strathbogie and building in Camperdown vic, then I'll get the capacity raised to 1000kg. Be sweet.
Also got a 2.92 diff from a 6 cylinder corty. Replaces the 3.7. Means I can tow in 4th gear. 5th strictly overdrive not far off commodore gearing now
Tony

Good luck with the move to Camperdown, I suspect you'll miss the mountains but not the cold. With Holden and Ford running gear your JBA will go for decades.

 

[gtrboyy]

Easy to get caught out by those weird issues especially when you don't know somebody before you has messed with.

Bet it felt good to finally work it out.

 

[JBAV6Tony]

Easy to get caught out by those weird issues especially when you don't know somebody before you has messed with.

Bet it felt good to finally work it out.

Yeh, thanks guys. I suppose one has to know their limitations. For me, anything internal I stay away from. This is because in my 20's I had Ford Escort Twin Cam cars Lotus powered...made for Bathurst. I had bad valves so off came the head. When I finished the job I had a rubber cone about 3 inches long left over. Turned out it was the oil drain tube at the side of the engine to be squeezed in between the head and the block...off came the head again. Then when nearly finished I was using a chain link on the chain drive cam chain and it slipped...off came the head as it went into the sump. Head gaskets were $120 each in 1980! x3. Later on I found out a Anglia one would fit for $12 as it was based on the Anglia block.

Since then I don't mind anything outside the engine but like in this case research pays off. The principle of the IAC I had to learn and I did on this topic in this forum, that it adjusts the idle through the computer. But it wont work correctly if the idle stop screw is screwed in fully. Once that screw is screwed out to obtain a normal idle speed the IAC will do its job and prevent stalling.

So thanks to the forum I'm on the road again with a great idle.
Tony

 

[Immortality]

Good to hear it's sorted.

The proper way to set the idle is with the engine hooked up to either a tech 2 or some sort of logging device where you can monitor the IAC stepper motor number of steps. In an ideal world it should be about 30 steps with the engine at operating temp and no excess loads (like AC or thermofan running etc). The poor mans method is the remove the intake tube, slowly cover the IAC intake passage in the TB and then adjust the idle down to about 500-600 rpm or just as it starts to run a little rough, then remove the blockage and the IAC will take over again and hopefully it's fairly close.

As a test and future point of reference, do the above without adjusting anything and see where the idle drops to, this way you know what rpm to target should you ever need to adjust it in the future.

 

[MikeC]

Working on stuff was much harder in the days before internet forums. If you weren't in a car club, you were forever doing things the first time, maybe with a Gregory's to help. Now you can see how others did things and ask forum members who've done it before for advice- that avoids so many pitfalls.

 

[losh1971]

I'm with you Tony, i rarely do much engine work or even trans work. To me it's where the big money comes out and potential for f-ups is generally higher and certainly more costly, if something goes wrong.
I look at from the view that if i can do most things, bar major engine, trans or diff, i am still saving plenty of coin. I don't have to be good at all things but if i am competent at most stuff then I'm good with that.