LS400 1UZ hard start problem

[Grady]

Hi Guys,

Need some advice on a problem I have been having.

I have recently completed a 1uz swap and the problem I am having is starting the engine when cold and warm (it tries to fire but fails), it takes around 6-7 times before it runs and idles.
Once it's running and warmed up a bit it will idle perfectly for about 3-4 minutes then start dying so I have to press and release the throttle for it idle fine again.

The car has been sitting inside the garage for the past month but it was running perfectly fine before then.

Things I have done/checked so far:-

• Replaced and gaped all spark plugs.
• Replaced engine temp sensor.
• Replaced O2 Sensors.
• Fuel Pressure Checked and perfectly stable.
• Checked resistance of all ignition-coil leads (resistance came back fine, but cannot rely on a resistance check).
• Checked resistance on both coil packs (again resistance came back fine, but cannot rely on a resistance check).
• Checked for Vacuum leaks over and over again and I am 100% sure there are none.
• Checked ECU for any leaking capacitors (no visible leaks).

The engine is a 1995 (non-vvti) (not-immobilized)

Any suggestions would be appreciated. 

[Z28DUNC]

Have you checked the throttle body? It could be sticking.

[plexus914]

How about fuel pressure?

Looking for leaks is not checking capacitors. Just sayin'.

All electrolytic capacitors with non-solid electrolyte age over time,
due to evaporation of the electrolyte. The capacitance usually decreases and the equivalent series resistance (ESR)
usually increases. The normal lifespan of a non-solid electrolytic capacitor of consumer quality, typically rated
at 2000 h/85 °C and operating at 40 °C, is roughly 6 years. It can be more than 10 years for a 1000 h/105 °C capacitor
operating at 40 °C. Electrolytic capacitors that operate at a lower temperature can have a considerably longer lifespan.

[Grady]

28 minutes ago, plexus914 said:

How about fuel pressure?

Looking for leaks is not checking capacitors. Just sayin'.

All electrolytic capacitors with non-solid electrolyte age over time,
due to evaporation of the electrolyte. The capacitance usually decreases and the equivalent series resistance (ESR)
usually increases. The normal lifespan of a non-solid electrolytic capacitor of consumer quality, typically rated
at 2000 h/85 °C and operating at 40 °C, is roughly 6 years. It can be more than 10 years for a 1000 h/105 °C capacitor
operating at 40 °C. Electrolytic capacitors that operate at a lower temperature can have a considerably longer lifespan.

Fuel pressure is great, just had the injectors tested as well to make sure they were operating as they should.

Thanks for the info on capacitors I always assumed a failure would be visible, I will replace them as a last resort as I would like to see suggestions from others as well.

[Cotswold Pete]

Had similar on my Mk4, cleaned up throttle body has cured problem.