Idle too fast

[MDyer]

After warm-up, my 77 wants to idle at "way too high" rpms. A quick punch of the accelerator only works some of the time.

Not long ago, I removed the air filter and housing prior to doing some grill work; I have not replaced it yet.

Could the free breathing be causing it to idle so fast? (The car exhibited the same symptoms prior to removal, but it's much more pronounced now.

[MDyer]

?

[sblake01]

Check you Air Regulator. Sometimes called an 'Auxiliary Air Valve'. If it was originally a California car, also check the Altitude Switch.

[GunnerRob]

I had a similar problem with my '75z after I replaced my fuel rail hoses. The problem was that after I replaced the fuel rail assembly, the fuel pressure regulator was touching the throttle shaft, causing it to not fully return to idle. All that was required was to loosen the hose clamps on the fuel injector hoses and pull the fuel rail out just enough so that the regulator didn't interfere with the shaft. On my car, these two parts are originally very close together, so it might be somewhere to inspect.

[TomoHawk]

Originally posted by MDyer

Could the free breathing be causing it to idle so fast?

Just opening the intake won't make it "breathe" better. You also have to open up the exhaust. Otherwise one end or the other will be your bottleneck.

[BuujinBejiita]

I am highly surprised no one suggested this, i have a 1977 datsun 280z as well mine idles at 1600 when i got it on the drivers side of the engine towards the front of the engine there is a big screw with a spring under it tighten it until you get the desired results, mine idles at aprox 900-1200 depening on weather. I have found this to be a good idle speed as it is not too high and not too low. If you cant find it i would be more then willing to take a picture of what im talking about.

[sblake01]

Well, since that is the 'idle speed adjustment screw,' I would assume that no one should have to tell him that. 900-1200 rpm is actually a bit on the fast side.

[BuujinBejiita]

Well, since that is the 'idle speed adjustment screw,' I would assume that no one should have to tell him that. 900-1200 rpm is actually a bit on the fast side.

I do agree it is kind of fast but its not that fast, i think it warms up the engine reletivly fast and it sounds really good at those speeds

[sblake01]

I do agree it is kind of fast but its not that fast, i think it warms up the engine reletivly fast and it sounds really good at those speeds

A properly operating Air Regulator will warm up the engine fast enough but too fast an idle just wastes gas but a Z motor sounds good at any speed.

[larsz]

Sounds like the bccd is stuck open or out of adjustment. Mine was disconnected & it was idling at 1400 rpm warm. You can try to adj. by loosening or tightening the screw or nut at the bottom of the diaphram or disable it by running the wire to the pos. + of the ballast resistor & see if the idle will come down. It worked for me.

[sblake01]

Sounds like the bccd is stuck open or out of adjustment. Mine was disconnected & it was idling at 1400 rpm warm. You can try to adj. by loosening or tightening the screw or nut at the bottom of the diaphram or disable it by running the wire to the pos. + of the ballast resistor & see if the idle will come down. It worked for me.

It's a 280-no ballast resistor.

[Gav240z]

I have not had many experiences with L-series injection setups however I've heard a few people say that their o2 sensors have caused this sort of thing before. However I wouldn't recommend going out and buying one to fix the problem. From my experience it is better to find what's causing the problem and replace that than guess and replace all sorts of other items.