3RZ hot start idle issues
09-25-2014, 07:06 AM
#1
3RZ hot start idle issues
I am hoping you guys can help a transplant out. I have a 3RZ swapped into my 85. I'm absolutely in love with the motor. The only issue I have is an idle problem when starting my truck when it is warm. For example if I run to the store when I come back out and start up my truck it idles very rough and low. The problem does not exist on cold start and also goes away after driving for a little bit. I'm trying to diagnose it and I'm wondering if any of you have come across this. Thanks!
10-03-2014, 02:34 PM
#2
Registered User
Old thread, but I've dealt with this before if you are still looking for an answer.
Two parts to this: 1. Heat Saturation and 2. Swapped parts/engines.
1. When under normal operation, the IAT (Intake Air Temperature) sensor normally sees air that's about 80-90 degrees on your normal sunny day. Usually 10-20 degrees higher than the ambient air temperature. When you shut off your engine and leave it for a little while, but not long enough for the engine to cool off, hot air from the combustion chamber "saturates" the air intake all the way to the IAT sensor. Now it's sensing some very hot air so it retards the timing when you go to start up your vehicle. Once driving again, the incoming air (80-90 degrees) cools off the IAT sensor and things return to normal.
2. When everything is bone stock, this is usually not an issue since the engineers compensate for this by programming the ECU to adjust for it, or there's extra airflow to cool it off. However, when you start swapping parts/engines from other vehicles it'll show up since it's not the manufacturer's original design.
Hope this helps. Short answer is: there's no way around but doesn't hurt anything.
Two parts to this: 1. Heat Saturation and 2. Swapped parts/engines.
1. When under normal operation, the IAT (Intake Air Temperature) sensor normally sees air that's about 80-90 degrees on your normal sunny day. Usually 10-20 degrees higher than the ambient air temperature. When you shut off your engine and leave it for a little while, but not long enough for the engine to cool off, hot air from the combustion chamber "saturates" the air intake all the way to the IAT sensor. Now it's sensing some very hot air so it retards the timing when you go to start up your vehicle. Once driving again, the incoming air (80-90 degrees) cools off the IAT sensor and things return to normal.
2. When everything is bone stock, this is usually not an issue since the engineers compensate for this by programming the ECU to adjust for it, or there's extra airflow to cool it off. However, when you start swapping parts/engines from other vehicles it'll show up since it's not the manufacturer's original design.
Hope this helps. Short answer is: there's no way around but doesn't hurt anything.
10-04-2014, 04:56 PM
#5
Registered User
Yes, I realize that. The vents for drawing in air is different on the body from a 2nd gen to 3rd gen 4Runner though, among other things.
I just upped my idle speed and called it good.
I just upped my idle speed and called it good.
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