rough idle on my 92 sc300 with 230k on it. after maybe 30 sec of running the idle drops and bounces back up continually (from around 500 to 750 then back) and shakes the car (reminds me of a cammed v8) there are no check engine lights, the o/d light flashes but i read that its from a speed sensor on the trans so i don't think that's the issue
things done:
ecu repair
12v mod
new plugs
wire set
cap and rotor
cleaned throttle body
new fpr
cleaned iacv
pcv valve
need help so i can smog it

 

Fuel is something that is springing to mind to check for next... ie injectors and lines

A few more details on the engine's overall state would be helpful,

What's it like when you drive it?
Problem only occuring during cold starts? etc
Also maybe look into your Mass air flow sensor

 

engine seems healthy, haven't done a compression test on it yet. no smoke out the tail pipe. this happens only on idle, on both cold start (after siting for a week ) and after i've been driving for a while when its warmed up, also when i get to a stop. while driving everything is fine. no over heating and it downshifts fine when i floor it.
haven't checked the injectors or the maf. is there a way to test the maf or just replacing it with a known good one. i've read that cleaning it might cause more damage than good.

 

Personally can't verify the information on whether cleaning would make a difference or not....

But in terms of the MAF sensor, I would try unplugging it while running and paying attention to the motor for changes in behavior,
and it would also be good idea to replace with a new one as a method of checking too

 

cool ill try that tomorrow and ill post an update. ill also do a more thorough look into the vacuum lines as i just did a quick glance at them earlier

 

Having 1:1 issue with my 92 SC400. it only shakes on idle.
I got suggestion to check catalytic converter. It might be clogged up or smth else. Gases on idle having troubles passing trough it. I wanted to get some test pipes and check if that helps, but had to spend money on other problems in car.

Will follow.

Good luck on finding.

P.S I will check my compression soon will give you an update.

 

well it took a while because i was busy but i did end up disconnecting the maf on my sc300. the idle doesn't change but the check engine light did tun on. so my guess is that it is bad. but why wouldn't it turn on if it is bad??

 

Well...if nothing changed after unplugging the mass air flow sensor to me that seems like the issue, but as you said it caused the check engine light to come on, so in terms of the maf, wouldn't hurt to swap it out... and a bit of comfort, those early JZ motors are WAAAAAAAAAAAAAAAAAAAAY easier to wrench on then a 1UZ motor.