Strange idle when cold

[fattima]

I was driving this evening the engine was cold and I noticed at idle engine revs were going up and down from the normal idle (900ish RPM) up to about 1100 RPM. It was not erratic almost a cycle once the car warmed up it stopped and behaved as normal. It's an NA6 with the timing at 14 degrees, I had the headlights on but no other extra electrical loads.
This has only happened once and am curious if anyone has an idea what would cause this. Any ideas?

Thanks

[Juffa]

I'm thinking O2 sensor. Give the search facility a workout and you should find a number of previous posts on the subject.

J

[fattima]

Thanks Juffa,

I will make up a test light tonight and see what it indicates, did a search and found a link to the error codes. New to the world of engine management, more used to a pair of side draught carbies!

[Fatty]

i was thinking it might indicate some gunk near the idle control valve thingy. isn't this a fairly common issue ?

[fattima]

Made up a test light tonight and checked error codes, there were none. I'm not stressing over it, I'll see if it happens again.

[fastfreddygassit]

i was thinking it might indicate some gunk near the idle control valve thingy. isn't this a fairly common issue ?

I concur
plus, if the engine was cold, then the O2 sensor wouldn't be "online" as it hadn't warmed up (na6 sensor is not pre heated).
dunno....

[fattima]

I'll see about giving the throttle body and idle control a clean.

Thanks guys

[Fatty]

just be careful what stuff you use to clean it. if you use the wrong stuff (carby cleaner for example) you can destroy the gaskets or seals or whatever they're called, on the throttle body.

[Fatty]

also , i forgot to mention that my car used to do this.

the way i fixed the problem was by switching to forced induction. it seemed to blow all the built up gunk and sh*t out of the intake... problem solved.

[fattima]

Cool, can I borrow your turbo setup till my car runs OK

[Boags]

also , i forgot to mention that my car used to do this.

the way i fixed the problem was by switching to forced induction. it seemed to blow all the built up gunk and sh*t out of the intake... problem solved.

Gold.

[fattima]

Well I have a day at Winton coming up, tough way to have to fix me car

[Fatty]

my post was a bit humourous, sure. but i was serious too. so yeah, track day should sort you out.

[hamish71]

I have an NB8B with a smilar proble. Hvae had the injectors and fuel rail cleaned, cleaned the tank (additive) about 5 tanks in a row, and after spending about $1000.00 it still does it every cold morning. Almost sounds like a bridge port rotary, but as soon as it gets in the normal temp range, its perfect.