My 1986 Nissan 300ZX Turbo has 60,000 careful miles on the odometer. It began stumbling, like running on 3 cylinders, when started cold. Time of day and moisture make no difference. New Cold Start and Air Flow Sensors have helped a little, but it still has the stumbles about half the time when started cold. Any ideas?
Has the maintenance been kept up? Has it been consuming oil?
On a car this age I’d suggest starting by bringing all the ignition components (plugs, wires, rotor and cap) up to date new. When you remove the old plugs, “read” each one per the attached chart.
That’ll tell you a lot about what’s happening inside the engine.
Because of the age of the car I’ll also recommend a compression test.
Add to car description. Car maintenance is up to date. It does not burn oil. Stumble lasts a few minutes, then it runs great.
Off hand, I’d say that you maybe in the early stages of bearing failure of the turbo. Do you use synthetic oil?
I do not use synthetic oil. Why would the turbo only affect the car during cold starts?
As the bearing begins to drag its going to be harder to turn, especially when cold. The engine would act like the choke pull off isn’t working. BTW, if it is carbureted, this would be another possibility.