ok i got a 1992 ls400 and i replaced iacv and the problem with the car is that rpm goes from 500 to 1500 like every min or so, but this dont happen till the engine is at the normal temp. So when i turn the car on it will run for like half an hr normal then it will start ideling up an down but before i replaced the iacv it would turn off. So the biggest problem is that when this happens the car has no power it will like take forever to get to 25mph its like its a one cylinder car not 8 and some time it will have normal power. So i took it to the mechanic and he couldnt figure anything out bc there to many sensors, so my ? is did anyone had this prob or do anyone no what this is.I really like the car and i dont want to sell it so please help me figure this thing out and there is no cel on the cluster. Some people told me its ecu or throttle body sensor or egr or needs a tune up but i dont want to spent money if it aint gona fix d problem and i dont no if i can make to the lexus dealer to getit checked by them so please help me and thanks in advance....

 

the mechanic was right when he said the car has alot of sensors..but if the sensors are bad you will get a engine light.. im pretty sure
it could be a number of things.....did you replace the iacv with a used one?
sounds like the iacv is the problem..maybe it needs cleaning

check for any codes... check for vacuum leaks check spark plugs and wires...

 

maybe the tps is bad?

 

yes the iacv was used but i drove the car and that was in that car didnt have any problems other than tranny so i now that iacv is good and its was cleaned and i was thinking about the tps bc each off them is missing the bottom screw so im kinda thinking that maybe tps bc there is two off them and they look the same other then having a diff # on them are maybe switched so please if anyone can tell me the # off the tps and where they go i know u cant mix the plugs.The only thing thats on is trac could that do anything with it bc twhen rpm gets to 1900 it just goes down it will not go over 1900rmp so i stay really light on the gas and just drive slowl.The trac light was not on until i took the battery off and now it stays on so what could that be, and i would love to get a cel but i just dont have one so im just thinking this weekend taking the egr valve throttle body maf and iacv and cleaning it and replacing all the vacum lines with new ones so before i do this any ideas what the problem is.

 

yea if your missing screws that is probably your problem. get some screws back in and go from there. i think the screw sizes are 8/32 x1/2inch