ok well im about to buy a gtu that has a jdm motor T2 1990 about roghly 30k miles. it has an idling problem when the engine gets warm the idling goes up and dow from 1,000 to 1,500. i figure maybe a tune up will do since it may be a misfire needs new spark plugs or i should look for vaccum leaks. wat can cause this? has anyone ever gotten this. im thinking can it be the turbo? can anyone help me a bit?

 

oh i forgot to mention on high rpms when you drive it yeah it goes awayy

 

Surging idle can be cured most of the time with correct TPS and idle speed adjustments. First, make sure the TPS resistance is set to 1000 Ohms, engine fully warmed up. Then go back and adjust idle speed (initial set connector shorted) to the 700-800 range. When the idle speed is adjusted too high, the system will send a fuel cut signal which drops the idle. When the idle drops too low it then raises it to the preset level but that's too high again so it sends the fuel cut signal. You end up with the up and down idle which is basically harmless, but very annoying.