Idle speed keeps jumping around

[aa23]

My car usually idles at around 800 rpm, going by the dash tacho, but once or twice a day, it will jump to 1200, and another time up to 1800, then after driving to the next set of lights, it's back to normal.
Sometimes, restarting the car brings it back to normal, but not always.
I mentioned it to some wanker of a mechanic, whom i'll never go to again, and they said the throttle body was all clagged up, and $180 later, there's no bloody difference.
I reckon it's electrical, and i'll happily take it to someone who can fix it, but it's such a hit and miss thing with some mechanics, that want I to try and get a better idea from this forum, before spending more money that I can't afford.
Thanks.
Kenny

 

[death-from-above]

Changed spark plugs recently??

 

[aa23]

1st up, thanks for reading and replying
Yeah. The thing was supposed to have had a major service and tune, and it did get new plugs.
It was running okay before the service, but i'd only had the thing 2 months or so, and had it serviced before we were going away, (in case it never really had been) and it runs okay, except for this damn idle speed that keeps changing.

 

[natsvr]

Hey Kenny try resetting the IAC. To reset the IAC (Idle Air Control) valve,remove the engine fuse or the -neg terminal on the battery for 1minute or so then, switch on the car & hold the engine at 3000 or so revs for 10 seconds, this should do the trick.

Hope this helps
Nathan

 

[aa23]

Thanks Nathan. I'll give it a try tomorrow, and let you know how it goes.
If it does fix the problem, any idea why it happens in the 1st place?

 

[aa23]

Okay, i tried the negative disconnect, then the 3 thousand rpm's, and it still didn't work.
But after reading your advice, maybe i didn't disconect it for long enough. Was only about 10 seconds or so. Was also suprised that the radio worked again, as I thought they were supposed to lock you out if you disconnect the battery terminal.

 

[natsvr]

Well they are supposed to, but i think its for a longer period than 10 secs.The better bet is to take the engine fuse out.By the way the revs should drop from 3000 aswell by it's self.

 

[aa23]

I'll take back my reply, as it does seem like it's fixed it. I sems to rev a little harder than i think it should from a cold start, sort of like a carby with a choke, but it only stays high, about 1200 rpm, for about 10-15 seconds. I've done a bit of driving since i last posted, and it hasn't really done the idle jump, so i'm happy as a pig in ****.

Thanks for the advice natsvr.

 

[DJ Majah]

My VS revs at about 1200 too for that long when I start it. Just the computer checking flows and responses before it drops to idle. Its a good system.

 

[natsvr]

No probs Kenny, happy to help out.