Car: 1978 280z

When starting, the car idles properly at about 800 rpms; however, if I wait a few seconds the car's idle will increase to about 2500 rpms. What sensor would cause this? If not a sensor, what else could be the culprit?

I should also note that while driving the car, the car will idle between 2500 and 2700 rpms. In gear the rpms will go as low as 1200 but I haven't fully tested to see how low the rpms will go.

Thanks

 

Could a number of things, but my first guess is going to be a vacuum leak at the manifold. Then I would guess the BCDD (Boost Controlled Deceleration Device, it's located under the throttle body). Testing the BCDD is easy, just pull the vacuum line off it and plug it up. Vacuum leaks, use a can of carb cleaner or a propane tank and spray around the intake and vac lines until the idle changes.

 

My '77 280 was doing the same thing. Now that I've had the whole thing rebuilt (have'nt installed it yet) I'm not sure. One thing I found out to be it also could be the cold start timeswitch. I bought a new on from autopartswharehouse.com. Lowest price I could find.

 

try the tps or your timing seems to make it go away. weird, but thats what mine was doing.

 

Thanks for the quick response. It ended up being both the boost controller and the water temperature sensor. Now the engine sounds perfect. Thanks.

 

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