My 90 240sx fastback is idleing strangely. It goes back and forth from about 600 rpm to about 1100 rpm every 20 seconds or so.
When it drops to 600 the is a repeated pinging or ticking sound. Very light, i can only hear it when the window is down. Then there is one louder click and the idle jumps up to 1100. It stays there for about 20 seconds and then there is a light thud sound (not sure how to describe it really, its hard to explain such light sounds). Then it drops back down to 600.
Anyone know what is causing this?
Thanks,Rob
240sx strange idle
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s13sr20chris
- Posts: 4148
- Joined: Tue Jun 10, 2003 9:32 am
- Car: '89 Nissan S13 w/redtop running 13psi and not leaking fuel anymore
- Contact:
I just figured out today that it only happens with the a/c on. It does it to a lesser degree when only the fan is on but with the a/c off. With the fan switched to off it seems to idle steadily at 700rpm. Also, it's a manual. But there's more.
When i press the brake pedal the rpm's drop by 100, then when i let off the brake, they go back up 200 then settle back down at 700rpm. Also, when the a/c is on, when the rpm's drop, the resistance in the brake pedal drops. When i am at a stop sign in neutral with my foot on the brake and the rpms drop the brake pedal moves down closer to the floor under my foot. This makes me think that it is perhaps a vacuum leak (?) which is affecting the brake booster and idle. Can the a/c also affect the vacuum? But i'm still not sure what would cause those types of sounds.
Finally, on a side note s13sr20chris, you helped me out last time with my clutch and i forgot to post a thank you so i'll take the time now. Thanks for the help with the clutch and the help now.
When i press the brake pedal the rpm's drop by 100, then when i let off the brake, they go back up 200 then settle back down at 700rpm. Also, when the a/c is on, when the rpm's drop, the resistance in the brake pedal drops. When i am at a stop sign in neutral with my foot on the brake and the rpms drop the brake pedal moves down closer to the floor under my foot. This makes me think that it is perhaps a vacuum leak (?) which is affecting the brake booster and idle. Can the a/c also affect the vacuum? But i'm still not sure what would cause those types of sounds.
Finally, on a side note s13sr20chris, you helped me out last time with my clutch and i forgot to post a thank you so i'll take the time now. Thanks for the help with the clutch and the help now.
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s13sr20chris
- Posts: 4148
- Joined: Tue Jun 10, 2003 9:32 am
- Car: '89 Nissan S13 w/redtop running 13psi and not leaking fuel anymore
- Contact:
heh, no prob. the lower brake pedal can be caused by lower idle. when the idle gets really low you can loose vacuum. the one-way in the vacuum hose to the booster should lessen that, but it may be leaking. it kinda sounds like your idle is dropping when the a/c compressor kicks on. in which case that is pretty normal. you can bump up the idle to help some but it will pretty much always do that. now, if its stalls thats too much.