mmartin888

Thanks in advance, 92 sc400 stock no mods at all

issue started rough idle going from 1000 to 2000, no power and glowing red cats with loose rattle
decided to tune up found right hand rotor had fell apart and caused a deep groove in housing

replaced right housing , both caps and rotors, wires ,plugs,both coils

fixed the power and the glowing cats

issue now is only in park the rpms go from 1000 to 2000 back and forth and in drive the rpms stay high around 1500 to 2000 while driving

questions
could have the glowing cats burned out the 02 sensors and cause a rough idle

could it be a timing issue

could it be the loose pieces in the exhaust causing the rough idle in park only

could the IAVC cause just the rough idle in park and if so why does it cost nearly 1000 dollars

easy method to check spark plug to see if it firing at the cap

MrBrock

Do you have a check engine light on? Bad O2 sensor would probably throw a code.

Do you have a high idle at cold startup or just when it warms up? If only when warm, thats probably the IACV (and that can be cleaned, search and try that before replacement), if high from cold startup, you probably have a vacuum leak somewhere.

Probably not a timing issue.

You can get an inline spark tester/indicator for like $5 at any parts store.

Side note: Idle going up and down is because of the way all fuel injected cars are programed now. When RPMs are above 2000 and throttle position is at zero, the ecu turns off the injectors. Like when you're on the highway and let off the gas, this saves fuel. So what's going on with your car now is that the IACV or vacuum problem is causing the car to rev up but once it gets over 2k rpm the ecu shuts off the injectors for a sec till it falls low enough to kick em back on, think idle rev limiter.

mmartin888

thanks for the reply, no check engine light. Thanks for the info on the up and rpms makes sense. At start up it runs good roughly 1000 rpm but just for a few minutes like 3 then it starts going up and down. You can drive it and it is fine, rpms are still high but runs good. I am going to clean the IAVC today and look for vaccum leaks.