Hey guys. Installing factory cruise control, and after changing the throttle body, I can hear hissing from the engine bay, and for some reason idle is higher than normal (1.5k RPM ish) It's almost as if the throttle is on a bit. I'll have a squiz, but the first question, where is it likely to leak air on the throttle body? I didn't change the gasket (the sheet of metal between the intake manifold (I think) and the throttle body. Should I have?

sound like a vaccum leak, look for any hoses you have left off... metal gasket shouldnt need replacing. check youve done TB up tight enough

I had similar issue and turned out to be a hose I missed putting back on. It came from the fuel line and hooked into the throttle body - small little tube towards the underside.

There's an old trick where you use carby or brake cleaner. Some recommend an unlit propane torch. Spray either on the hoses when the car is idling and listen to see if the revs change or not. But WARNING: This stuff is flammable, so do not spray it anywhere that is super hot and can ignite! (e.g. exhaust manifold)

Apparently you can also use a....cigar! LOL

http://www.youtube.com/watch?v=zMok2y05jNE

Definitely a vacuum leak somewhere, as the guys have said, find the hose that is not connected.

Something just didn't seem right. And I was right. Popped the bonnet, localised the hissing to the throttle body. Comparing my old TB with the one I put on, I noticed what I believe to be the ISC screw to be almost rounded, so someone had been fiddling with it and rounded it in the process. Grabbed a trusty flathead screw driver, and turned it. The revs slowly dropped with turning, and the hissing faded out as I turned it too.

Serves to anyone facing a similar issue - check your vaccum hoses first, and then if the hissing is still there, check the ISC screw.

Am I right in this being the ISC screw? Can figure out the service manual.

Be very careful adjusting that screw (SAS stop screw) on the ISC. That's setup from factory to be the right spec. I believe there is instructions in the mitsubishi manual or in an aftermarket service manual from max ellery or gregories etc

That is basically the screw where the tb levers rest on and therefore adjusts the idling rpm. However it can mask any problems you may have on idle.

I'm almost be inclined to get a new tb from the wreckers than readjust that.

Be very careful adjusting that screw (SAS stop screw) on the ISC. That's setup from factory to be the right spec. I believe there is instructions in the mitsubishi manual or in an aftermarket service manual from max ellery or gregories etc

That is basically the screw where the tb levers rest on and therefore adjusts the idling rpm. However it can mask any problems you may have on idle.

I'm almost be inclined to get a new tb from the wreckers than readjust that.

It seems to be running fine now though? Idle is exactly where it used to be, and now no hissing.

Although I have noticed that the car sounds different under 100% load (sounds like a lower pitch V8 growl).

Is it definitely the ISC screw that we're talking about here? The one I adjusted is the sunken one facing the front of the car.

Idle bleed screw.