I have a 91 ls400 that when it warms up it surges between 800 to 1100 RPM's
So far I have taken the throttle body off cleaned it .
Chances the fuel filter
Changed the air breather.
Replaced the MAF sensor .
No codes
It runs and starts fine just surges oh we also cleaned the throttle position sensor. This thing is driving me crazy !Thanks Danny

 

Check Idle Air Control Valve.

 

Yes that's my next move . it van be cleaned and not replaced ? Thanks

 

I quite cleaned the air control valve and didn't change a thing so thank you for your help. I thank I will scrap the lexus out.

 

you can't just clean it, you need to test it to see if the solenoid still works.....

 

there is a test procedure in the service manual, for both the coil portion and the bearing portion of the IACV

if the IACV tests out fine on both the resistance checks and the correct movement while applying battery power, then at that point I would start looking at ECU caps as a likely suspect.

 

I can unplud it and it don't make any difference . when I unplug the MAF it don't change anything. May be the ECU then but at $2000 dollars that makes to expensive to replace that's more then the Lexus is worth . Lol

 

ECU's for your model are only $150 on ebay or at the junkyard, although they may require new caps, if yours or one from ebay needs new caps the cost of the parts is only $10 if you know someone who is skilled at soldering in tight places!

 

Where do you buy the caps if needed ? My tack ,speed o meter and every thing works just surges between 800 and 1100 rpm's