idle issue on an 88 k5

[root beer 88]

i have an 88 k5 with a 350/700r4/208
it has a stumbling idle and i think i know why but wanna post up on here to see if anyone else has had this issue or can shed some light on it for me

im new to the k5 thing so dont flame me too bad if its a dumb question lol

sometimes it idles around 1000rpm and sometimes 500rpm depending on the weather/outside temp but either way it kinda bounces up and down by 100rpm
cruising or getting on it and the problem disappears
ive replaced the map sensor and spark plugs and fuel injector connectors and it has new distributor cap rotor and plug wires

i have a bit of an exhaust leak on the passenger side that i cant tell if its coming from the manifold gasket or the gasket at the manifold y-pipe connection

my insinct is that the idle issue is a vacuum line but could that exhaust leak actually be the root of my problem?

any input is greatly appreciated

 

[British Slave]

Check timing, injector leaking, vacuum leaks.

 

[root beer 88]

Timing is dead on and the injectors are good... Is there and easier way to check vacuum lines than going through them 1 by 1?

 

[British Slave]

When I was chasing vacuum leaks on mine, I went to Auto Zone and bought an assortment of vinyl slip on caps. I disconnected the vacuum lines at the throttle body one by one and capped them till I found the leak. A good place to start is the thermac and cruise control. Make sure they are connected.

 

[4X4HIGH]

Sounds like the typical vacuum leak. Get yourself some carb cleaner and start spraying it around all the vacuum hoses, and all around the TBI unit (good chance it's the TBI base gasket) and when you find the leak the RPM will pick up.

 

[Confedneck]

i'd bet you have a blown out tbi gasket... 17 bucks at autozone, might as well replace it and check the vacuum lines

 

[root beer 88]

Im gonna get that exhaust leak fixed and replace the tbi gasket early this week... Is it a pain in the ass to just replace all the vacuum lines so i dont have to worry about them for a long time?

 

[GalDemSuga]

EGR valve!! Take a good look at it.

 

[root beer 88]

What am i looking for on the egr valve to know its bad?

 

[GalDemSuga]

A leaking diaphram. I had a pinhole in mine and caused the truck to run like crap. Also, the EGR gasket at the intake. Pull the EGR off and check it out and look to be sure that the EGR ports on the intake are not plugged with carbon buildup.

What am i looking for on the egr valve to know its bad?

 

[British Slave]

If you have a hand vacuum pump, you can apply vacuum to the EGR diaphram and check to make sure it holds.

 

[root beer 88]

so all my vacum lines and connectors were good and the egr and tbi gasket are good...

the leak was coming from the AIR/EGR tube off the passenger manifold at the fitting on the tube itself... i put some high temp silicone on there and the idle got better despite the manifold gasket being bad....

the next day the idle was worse than than to begin with but i noticed that the manifold gasket was blown out a lot more (possibly from more pressure with the fitting leak sealed?)

now that everything else is either replaced or ruled out my question comes down to...

is my idle issue being caused by the bad manifold gasket creating basically a giant vacuum leak since theres smog stuff attatched to that manifold and its letting atmospheric air into the system?

 

[4X4HIGH]

An exhaust leak has nothing to do with vacuum and wont affect the idle.

 

[root beer 88]

I just figured the AIR system used vacuum from the air injection pump to pull exhaust gas from the manifold.... How does that system actually work?

 

[Mav2u]

I second the EGR valve! Take a look at it. It can cause those issues also!

 

[4X4HIGH]

I just figured the AIR system used vacuum from the air injection pump to pull exhaust gas from the manifold.... How does that system actually work?

If you're talking about the AIR system (as in smog pump) that system is actually a belt driven air pump that introduces air (oxygen) into the exhaust to help burn any unburned fuel in the exhaust system after it has left the engine.

 

[root beer 88]

Oh... I swore from looking at it those tubes off the manifolds went into a vacuum pump (which i assumed was the AIR) towards the back of the engine bay on the passenger side and then out another tube forward to another vacuum lookin pump (i figured the EGR) and then ported through smaller vacuum lines into the TBI... Im thoroughly confused now lol

And i dont have a hand vacuum pump so is there any other way to check the EGR? Once i figure out which small fist sized vacuum pump that is lol

 

[4X4HIGH]

Pictures are worth a thousand words, take a pic of what is in question and post it here and we can tell you what the object in question is and what it does. There is no vacuum pump on a gas engine.

 

[root beer 88]

Ok so after taking a second analytical look at the setup i was completely off on the setup and 4x4high youre right on the way it is... The tube/fitting that had a leak goes to a y and then forward to the smog/AIR pump and the EGR is kinda tucked behind the TBI and air cleaner housing... The EGR looks easy enough to swap out for a new one but is there any way to test it without a hand vacuum pump? I just wanna be sure its bad before i fork out the like $80 for it lol

 

[Mav2u]

EGR should be less than $50 bucks! I'll check my maintenance trouble shooting guide for the EGR to see if there is another way to troubleshoot without a vacuum pump.

Although owning a vacuum pump/brake bleeder is a great investment for not to much money.