mlm0

1989. Auto trans, stock

Will a vacuum leak after the TB , cause the engine idle to rise or go lower?
If I do have leak, and additionally, will finding it with starting fluid cause idle to rise or lower.?

PatternDayTrader

Yes, and using starting fluid to find it is an excellent way to burn it to the ground. I suppose that's one way to solve the problem.

mlm0

Yes, what?

PatternDayTrader

Yes a vacuum leak will cause an erratic idle and yes starting fluid is probably the single most flammable product available to anyone who is not a Federal Explosives Licensee.

mlm0

I agree about srarting fluid, and I won't use it anymore, but the question was will vacuum? leak increase rpm or lower rpm

antfarmer2

Blow some smoke in it.

PatternDayTrader

In a general way it will increase the idle speed but I prefer to think of it as erratic because it may fluctuate up and down or otherwise behave in an unusual way.

PatternDayTrader

For what its worth; one of the best ways to find a vacuum leak is to take a propane torch and turn it on without lighting it, then move the tip around the suspected areas until you find the spot that makes the engine rev up. This is much safer than spraying carb cleaner or brake cleaner all over the place, and if self preservation is an instinct you possess then you will never, ever use starting fluid.

mlm0

Thanks, now I understand. Sometimes it takes me a while

mlm0

Out with the starter fluid, in with smoke or propane

Thanks

1993C4LT1

I know on my speed density 93, a vacuum leak raises the idle. On MAF engines, I believe the RPM is lower than normal.

Bodageta1995

. The last time I used my homemade smoke machine with a rubbe glove over the throttle body with the MAF removed on my 89. I got smoke out on the passenger side at the side of the throttle body but could never identity where it was coming from. I don't know if this is normal or not and would be curious if you get the same?

mlm0

yes yes yes,, on my 89 I taped up TB, AND I DID get some smoke from same area and i could not pin point it

1993C4LT1

Hmm, wish I could tell you where the leak is coming from. I would look visually for bad vacuum lines. Maybe spraying water in that area will help you find it. If there is a leak, and you're using water to find it, the engine will run rough when you find the leak.

jph46

I remember a post about the butterfly shaft in the TB with a leak. If your seeing smoke there's a leak. Hope you find it.

mlm0

i remember seeing it too i have repair kit, but cant find the repair link i use to have