Possible Vacuum leak after transmission swap

[1990suburban2500]

Hey everyone!

I have a 1990 3/4 Suburban 4x4, 350tbi 14 bolt SF, NP241C t-case that initially came with a 700R4, but had a TH400 swapped into it when I bought it.

I needed overdrive, and after doing some research i figured a NV4500 swap was the best course of action...maybe.

After a pile of work, beer and swearing, I can now say i have a Suburban with 3 pedals and a badass trans.

My problem is this, there was a vacuum hardline that came off the rear (firewall side) of my throttle body, and it ran down to the TH400, im guessing this was for vaccum operated up shifts, but i'm no expert. I blocked it off the best i could with a rubber cap and zip tie. My truck starts and idols very well until it gets hot, then the RPMs drop really low, and it hunts and sounds like its just clinging to life.

What do you guys suggest? Thanks for your help!

 

[Matt69olds]

Take the line completely out. Follow it up to the throttle body or intake manifold and cap it there.

 

[DoubleDingo]

Take the line completely out. Follow it up to the throttle body or intake manifold and cap it there.

^^This^^ They make threaded plugs that will fit the back of the throttle body. If it has a threaded nipple for the hose to slip on for the transmission, remove it and take it to the auto parts store to match the size. If it the tube is built in to the throttle body, just use a good cap to plug it. Vacuum leaks suck and will cause an engine to run in odd ways. I had an issue with multiple leaks a couple of years ago and it drove me nuts trying to diagnose the problem(s). Once I got them all fixed the truck ran so good.

 

[Vbb199]

It's for the vacuum modulator, shifts are determined upon manifold vacuum.

Cap it

 

[Matt69olds]

It's for the vacuum modulator, shifts are determined upon manifold vacuum.

Cap it

Not with a5 speed manual!!!