Low Idle BS

[Trevor loves holden.]

How good is the car battery? Does the needle on the revs pick up when you put a load on the engine, like changing in and out of gears, if no bounce on the needle then your IAC valve isn't doing its job so then its either wiring or the cars brain not communicating. The needle should bounce above 1000 then back down to around 800. the IAC, TPS, MAF and 02 sensors all work together if one fails then that can upset the computer, unplug the MAF and see if it picks up the revs.

 

[Davo_vx]

Ok so after tonight's battle I thought I'd made some headway but the mongrels playing up again. I swapped the battery with a fully charged one no luck swapped the maf no difference. I then swapped back the the previous throttle body with ica as immortality suggested and bam bullshit gone. It was idling up and not down switching between drive and reverse, rpm 1000-800, turning the fan on high had no effect on idle but it was idling at about 1200 in park engine already warm so sounded loud with my exhaust, I assumed that it fixied the problem and computer probably just needed a reset to adjust to other ica. Remembering mace engineering instructions of unplug positive terminal for 30 seconds than refit positive and start car hold rpm at 2000 for 30 seconds to reset computer and it's doing it again wtf? Should the idle change if you unplug the ica while running? I am guessing yes?

 

[Davo_vx]

One positive to come out of it is its isolated the problem, what's hilarious about the whole shitshow is it's the first thing I swapped when I got the s pac because I had already cleaned the one on my series 2 that got wrecked when I got rear ended. Had I have known that holden made TB changes between vx series might of saved myself alot of fun lol. I am guessing either the ica is stuffed or the wiring to it is considering when I unplug it doesn't do **** while idling?

 

[Immortality]

IF you unplug the IAC than it can't move so the idle speed is effectively fixed until you change the engine load like turning on or off the AC etc.

 

[Skylarking]

The older 4 cylinder Mitsubishi Magna’s had a fault where everything worked but intermittently you’d have all sorts of idle and run problems. It was a well known fault cause by the throttle body plug connectors loosing their spring tension and not being able to hold onto the pins to get accurate readings since vibration and bumps just upset the contact. Looking at the plug and connector springs would show no visible signs of corrosion or contact issue, same with the pins it mates to. You just can’t see low spring tension frustratingly, usually, but not always, you could wiggle the connector and create the fault you’re struggling with A new connector was available from Mitsubishi and cheap to buy and install, honest mechanics would know about it and charge appropriately. So mongrels within the industry would also know about it but try to financially rape their customers with completely unneeded work

So if you’ve tried everything else and nothing works, don’t discount such connector issues as @VFSV6FORME found similar in his son’s WH in this post (VFSV6FOME, sorry I didn’t post the above Magna issue but only remembered it after you found the problem).

One last note. especially to VFSV6FORME, vehicle manufacturers crimp connectors to wires as they are more reliable than solder, especially when vibration exists. Soldered connections can fail (fatigue?) due to vibration causing all sorts of intermittent problems down the tract.

 

[Davo_vx]

Today I went and got a Ica from repco didnt fix it. I am leaning towards it being the something to do with purge system/hose because it doesnt make sense that it ran perfect for abit then went back to it's old tricks after I changed tb, bearing in mind I only introduced two different sensors and reattached purge hose. I know now its definitely not those sensors so that only leaves something in the purge system or hose or bad wiring to one of those 2 sensors.

 

[Davo_vx]

Thought I'd do a compression test today just to rule out other problems, 190-185psi across all 6 cylinders pretty happy with those numbers considering cars done 210000kms. Still no luck fixing her though lol

 

[chrisp]

Here are a few pages from the service manual that might be applicable...

 

[Davo_vx]

Cheers for that crisp, that looks like a good manual you've got there. Did you download it?

 

[klrtim]

Howdy folks Tim Here also known as Gadgets. Love Em
Have you considered purchasing Advanced Engine Diagnostics and ALDL to OBD port cable. from envious customs Jason all under $160.00
I monitor
All o2 real time, as well as almost all fuel and electrical engine data. Read and clear Po Codes as well as capture freeze frame results.
Log all of them in real time and save to view results on my laptop while watching you tube clips.
Best tool ever and I have been spanering for over 30 years LOL

A pic of my VT / SS L67 Commodore