vacuum test

[qwerty247]

Ok i am trying the test with the carb cleaner to find a leak...
I spray it on the hoses etc and nothing happens, does that mean there isnt a leak?

what could be the cause of my slight rough idle on my 97 4.0 ?

thanks for any ideas?

ps.
new plugs, leads, arm, cap and o2 sensor (upstream)

[jeepdude10000]

have u cleaned ur throttle body lately?
that will cause rough idle, if u do clean it make sure u take out all sensors, and clean the IAC also.

[5-90]

So, you checked all the hoses. Did you also check the intake mating surface and throttle body base? Pretty much anything between the throttle valve blade and the intake valves can be suspect in a vacuum leak - be thorough...

It might also be instructive to "T" in a mechanical vacuum gage to read intake vacuum - branch it in on pretty much anything going directly to the intake manifold (MAP sensor, Fuel Pressure Regulator, what-have-you...)

5-90

[Matthew Currie]

I don't think there's too much point in testing for vacuum leaks, a difficult process if they're hidden, unless you've determined with a vacuum gauge if you actually have any leaks. Vacuum gauge is cheap and versatile and quick to use.

Using a liquid to test for leaks is possible and often works, but it can miss hidden ones. Mechanics often use propane instead, releasing it in the vicinity of suspected leaks. It will speed up the engine when you hit one. Of course, the disclaimer follows: don't do this if you're not properly set up to do it, and don't, don't don't do it indoors.

[qwerty247]

Thanks for the info !

I will try cleaning the throttle body, see what happens.

Its a very slight rough idle, its like its got hick-ups...runs ok then sudden quick drop and up again.

does that sound like anything familiar?