Weird Idle

[central coast person]

Hey guys, i was driving today and had no problems with my idle what so ever then tonight i drove off and tuned my headlights on and when i came to the traffic lights i was doing 1500rpm while sitting there, i looked to see if i was just stupid and had my foot on the accelerator but nope. I took off and then it happed at the next set of lights so i reved to 4000rpm and it droped back to the normal 700rpm.

I took off an came to a set of lights to see it was doing it again! i took off and before i came to a stop this time i stayed in 4th and when 5km before stopping and i could go under 1500rpm, down too like 500rpm but i came to a compleate stop and held the clutch in so as not too stall and it jumped up again!!!!!!!!!! (nothing mechanical is stuck if i can get under the 1500rpm while driving :S )

I got home in the garage turned my headlights off when it was stopped in there and was doing 1500rpm and soon as they went off it went to 700rpm.

Electrical problem most likely seeing as i could go to 500rpm while driving if i slowed right down in 4th.......

i dont know where to begin looking on the r33.....

[MissR34]

go talk to an auto electrician or your mechanic about it dude...... that would be ur best bet

[mad082]

there are plenty of things he can do before paying someone to look at it. various things can contribute to the idle speed, especially after lift off. first of all there is the old IAC and AAC setup. also the o2 sensor can contribute to this as well. i have heard of people with dodgy o2 sensors causing similar issues. i know that in the missus pulsar though that if i am driving and pull up, sometimes the revs drop to around 1200rpm for 3 or 4 seconds and then will settle down to the normal level after that. however in your case, because it dropped after you turned the lights off, it is more than likely going to be caused by the AAC. the AAC is the Auxilary Air Control. this is designed to alter the amount of air going into the motor (mostly at idle) to stop the engine stalling when extra load is put on the engine by such things as the alternator (when the lights are turned on) or the aircondition compressor.

[central coast person]

yeah it has done this before about 2 months ago when i used headlights. Didnt do it since then and i have driven heaps with my headlights and tonight it didn't do it......

It is a brand new engine but the wiring is original 171,000km

Alternator was taken from a mates skyline with only 38,000km. i also took the engine with wiring harness and lots of bits. even the exhaust manifold with a O2 sensor on it. My sensor is old and rusty and i should have swapped it when i did my engine.

Anyway, no progress on the idle as i did stop tonight a few times and it just was normal, i knock it into neutral just before i stop and it idles at 1200rpm and then when it completely stops in neutral it idles at 700rpm so it was being normal tonight. Unlike last night staying at 1500rpm without budging.