Vacuum testing question

[Chrispbrown36]

I have suspected a vacuum leak for a bit now and finally broke down and bought a gauge. 1987 Chevy V10 350 tbi auto. What she is doing: the idle seems ok but when I put her in reverse she idles way down and sometimes dies. It doesn't happen often but sometimes it will do the same thing when put in drive. Most of the time she runs great going down the road, every now and then she stumbles on take off if she hasn't ran for very long. Cruising down the road, if I let off the gas she will back fire every now and then.....not a major backfire, more than likely I am the only one that notices it. What I have done: new intake gasket, new distributor gasket, new idle air control valve, new map sensor, new valve cover gaskets, and new pcv valve.
When I hook the gauge up the needle jumps from the high end of the normal area to above the normal area by around 1 or 2 inches of mercury and then drops back into the normal area. The idle gets pretty rough when I disconnect the vacuum line (coming off the back of the intake going to the brake booster) to hook the gauge up, which probably accounts for the bouncing around, but should the idle get rough like that? Am I hooking the gauge up in the wrong spot?
Any help you guys can give me would be greatly appreciated.

[Gregski]

well what I would do is go to the auto parts store and buy three feet of every vacuum hose / line you have attached to that carburator then take one off at a time and cut a new one to size and slip it on, these hosers tend to crack, they might look all nice and good, but they are pourous (sp) this can be a cheap fix or just a good thing to do on an almost 30 year old vehicle

also post some pics of your engine so we can take a looksie

just trying to help
Greg

[Chrispbrown36]

I just thought of this, not sure why this didn't occur to me earlier. When I was changing the valve cover gaskets the piece I circled in the picture broke off. I have been debating on what I should do to fix it since I haven't seen the part anywhere. First question, would this be causing a vacuum issue? Second question, if it is the source of my problem where can I get a part to replace the broken one? Could I use a push in breather with the tube and run it back to the throttle body?



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[Chrispbrown36]

I hadn't considered just replacing all the vacuum lines....that sounds like a good thing to do anyway. I will do my best to get a picture up tomorrow....thanks for the quick reply Gregski.

[Gregski]

Originally Posted by Chrispbrown36

First question, would this be causing a vacuum issue?

it could, to test it just plug this port on your carb and see how she runs with it closed off

Originally Posted by Chrispbrown36

Second question, if it is the source of my problem where can I get a part to replace the broken one? Could I use a push in breather with the tube and run it back to the throttle body?

Yes, this is just Positive Crancase Ventilation that sucks the fumes out of the valve cover back into the carb for emission controls, it does not have to go into the carb, but for SMOG purposes on your truck it should, just go to a junkyard with your broken piece and buy a used one

Very clean engine is that really what the 87s looked like, can you share a pic with the air cleaner housing removed please?

[Chrispbrown36]

That isn't my engine...just one I found online that showed the part that broke well. My engine is a tbi not a carb. On these motors the pcv valve is on the left valve cover and there is a breather on the right that comes out and then there is a hose that runs back into the back of the throttle body.
I believe that motor is from a truck newer than an 87 though because it looks like the tube coming off the air filter housing goes out too far to the left....mine comes out slightly to the left and then runs to the left of the radiator. Otherwise, yes that is what the 87's look like. I will get one up tomorrow of my engine and I will take the air filter housing off for ya too.