Hey guys this is my first thread, I’ve had my 92’ Sc400 for about a year now has 177k miles, so far I have replaced the water pump, & timing belt, thermostat, spark plugs, rotors and caps, with fresh oil every 3k miles
It had gave me a code for bad cam sensors, did some research and replaced the timing belt and timed it right, I thought that would fix my idle problem but it didn’t. No more cam code but now It gave me a code 71 EGR I replaced the whole EGR from one off a 94’ LS400 drove it for about 150 miles... so far no CEL but my idle has been at zero when I’m at a stop ever since I’ve owned it. I was wondering what reasons could cause this, I live in Vegas and smog is required to register my SC
I feel like it’s lacking power, thinking it could be a vacuum leak... not sure
On a cold start it idles around 600-700rpm then lowers rpm to Zero when it starts warming up.
Any help would be appreciated
Thank you

 

You could have a bad coil, that usually shows up as low rpm and seems down on power as you only run on 4 cylinders when that happens.
do a search on here for sc400 or 1uz and bad coil. generally you unplug the coils one at a time with the engine off, if it starts and runs the same, then that was the bad coil.
if you unplug the coil and it wont start, or starts and runs worse than before, then you unplugged the good coil.
If both of them make it run worse than before, then both your coils are good and the issue is somewhere else.
another common problem on these is the ecu's going bad, been happening alot lately due to the age of these cars, but since you are getting check engine light codes that went away I think your issue is the coil.

 

I would agree with @Ali SC3 . Troubleshoot the coils, if you haven't replaced them, since your cold idle is still low. Cold idle should be 1K to 1.1K. I've been troubleshooting my low idle for about a year. I'm waiting 2 more months to confirm if the last fix actually worked, since every time I change something it will work for 3 months then it will revert to hard start and low idle, this was my las fix before I have to pull the ECU, since I'm at my last straw, with my 400

 

Seems like vacuum related to me. These cars have so many vacuum lines, make sure you don't have a line off or leaking somewhere. I don't know the 1UZ like I do the 2JZ but seems like vacuum. When you give the car throttle does it run ok? It's just low idle?

 

I have checked my ignition coils and they seem fine, I disconnected one at a time and tried to turn the car on... didn’t want to start
I’ve drove the car for 700 miles so far and the CEL just turned back on today with codes 14, 15, & 21
14 & 15 have to do with bad coils I found out by doing some research and the code 21 is for an o2 sensor
Any help would be appreciated

 

So i asked earlier, does it run when you give it a little throttle? Does it run smooth when you do? Need more info to help.

 

theres a little hesitation when I floor the throttle
feels like it’s pulsating
On a cold start it’ll idle high and as soon as I put it in gear it drops to zero