Hi, my dad has a 1990 2-door 4Runner, 3.0, Auto, 4X4. I runs really rough when you first crank it up and drive for a while and it gets better as you go but not perfect. It stutters and misses really bad. It doesnt do it all the time though. It does most of the time but not all the time. He took it to a very good reputable shop and it wouldnt do it while it was there. He said bring it back when it does it again but you cant predict when it does it. It doesnt throw a CEL. Any ideas?

 

Test for vacuum leaks? When was the last tune up done?

 

how can you test for vacuum leaks? is there any special procedure or tools you need?

 

anyone else?

 

You can do a basic test for vacuum leaks by spraying a liquid (WD-40, water, pee...) and seeing where it bubbles.

 

would a vacuum leak be off and on though?

 

Depending on where the leak is yes. Going from Park to Drive pulls vacuum.

 

well, weve studied ans discovered that it only does it when the humidity is high or if its rainy out. all the other times its fine.