1979z - 1500rpm cold idle

[Kevin Livesey]

Hi All, I have a bit more time for browsing as my 1979 Fairlady Z is back on the road after a 7- year ground up restoration. I do have 1 issue though: The engine will not idle below 1500 rpm when the engine is cold. It also has a hesitation when accelerating with the engine cold or hot. It had been dismantelled and re-assembled with new rings, bearings and gaskets. I've fitted new vacuum hoses, cleaned all the electric terminals and also swapped all of the following as a means of trying to find the fault by trial and error: Distributor, plugs and leads, airflow meter, fuel regulator, ecu and fuel filter. My next step is the bcdd valve. I am really keen on solving the problem so I can enjoy my car the way it is meant to be.

Please feel free to give me some advice.

[ZCurves]

When you reassembled, did you make sure that the Idle screw on the throttle body was set to FCM specs? Have checked the Thermo-Time / Water Temp sensors?? A bad Aux-Air valve will also cause a fast idle/'rich' idle condition. I am thinking that there is a bad sensor and some adjustments needed on the Throttle Body. Double check for a vacuum leak and correct timing.

Do you have the EFI Manual? Search the Forums for '280zFuelInjectionBook' or PM me with your email address and I will send it to you.

[Kevin Livesey]

Hi Andrew, I have consulted the 280z fuel injection bible. The components and diagram in it is slightly different to the system on my car, ie-mine does not have the auxilliary air valve or the cold start valve. It is worth mentioning that my car is a Jap import with a 2 liter motor. I have played around with the Idle screw- it does make a difference to the idle, but I cannot get it below 1500rpm when the engine is cold. When the engine is hot, the engine will quit when I adjust the screw closed too far. I have also adjusted the forbidden mixture screw on the AFM, but with it closed completely and the idle screw closed completely the car still idles at 1500rpm when cold. I will change the thermo and water sensors as well. I appreciate your help.

[Z Tyler Z]

Whats the idle when it's warm? Could this high idle be the result of the automatic choke? My 76 idles high when it's cold out until the engine warms up.

[Kevin Livesey]

Hi, this engine is fuel injected and does not have a choke, when warm the idle is good, but there is a hesitation when accelerating.

[sblake01]

Sounds to me like the idle is just fine. No choke but the EFI cars do have a fast idle system that consists of the Auxiliary Air Regulator, which basically bypasses the throttle plate during warm up, and the water temperature sensor which is a heat dependent resistor that richens the fuel mixture druing warm up. A bad water temperature could also cause hesitation.

[Kevin Livesey]

I,ve changed the thermotime and the water sensors. This made no change. Yes the idle is fine when the engine is warm. When the engine is cold it takes about 10 minutes to warm up with the idle being about 1500rpm and slowly working it's way down. I removed the cold start valve(auxilliary air valve) which is below the throttle body and tested it outside the car and found it to works fine. It takes the time to close it normally takes for the engine to warm up. I do find it annoying to wait 10 minutes though idling at 1500rpm. I just thought that 1500rpm idle when cold was too high. This valve heats up electrically and can only fully close when fully heated and does not rely on any sensors.