84 Suburban Idle issue

Here is Eric’s video on vacuum leaks –

http://www.youtube.com/watch?v=9CPqbaSg … h5ma49U%3D

I would also check for fuel pressure. When was the last time the vehicle was tuned up?

Quoted From college man:

try tapping your IAC valve with the handle of a screw driver to see if the idle changes. if the idle does change then
replace the IACC8-)

There’s no idle air control valve on this beast. That truck probably has a Quadrajet carb on it. Those things are beastly when tuned right, but hard to get tuned right. You may try backing the idle metering screws out half a turn on each side and seeing if that helps at all. If not, a rebuild may be in order. I’m going to refer this to my buddy Yarddog who is our resident carb guy. Also, does that carb have the metering solenoid built into it? You will know because there will be a connector on top of the carb. It may be bad. Does the truck run fine otherwise? If so, you may just be dealing with the idle circuit of the carb. You may also want to try blasting it with some carb cleaner for kicks, in case there is some gunk keeping the throttle plates stuck open, which would be a vacuum leak in itself. These plates are at the bottom of the carb, under the venturis, not the butterflies on top of the carb. I would check this along with checking for other vacuum leaks as suggested.

+ 1 on the above posts regarding vacuum leaks. spray some carb cleaner around the base of the carb , see if the idle changes. you can also hook up a vacuum guage and see if it jumps around or stays s

Quoted From yarddog1950:

Sounds like your battery and alternator are not involved in the problem.
Was the truck running well before this happened?
Checking for vacuum leaks would be among the first things to do. Then check your ignition timing with a timing light. (If it’s off, you may bring up the idle speed by correcting the timing.)
Most 1984 Suburbans came with 350 V8s and computer controlled Quadrajets. Like all carbs, they may need overhaul as frequently as fifty thousand miles. If yours hasn’t been rebuilt in some years or it has over 60K miles on it, it could easily be the source of your problem.
Check your ignition timing first, then check spark plugs. If they’re carbon fouled, suspect the carb.
If the carb is at fault and appears to need adjustment, you need a digital multimeter (DVOM) and the specs for your settings.

Yeh! Thanks Yarddog!

Edelbrock sells two different 4 barrel cabs, one a copy of the Carter AFB and one a copy of the Q-jet. The AFB type is usually chrome finished and is short from front to rear so it fit on twin 4 barrel manifolds. It’s very easy to rebuild. The Q-jet is not chrome finished.

Some Edelbrock AFB type carbs are not “chrome finished”. They are either brown or or shiny, not actually chromed. Yours looks like it was shiny but it’s just dirty from off roading. The throat looks fairly clean.
I think your low voltage is from low idle speed. This is corrected by eliminating vacuum leaks, correcting ignition timing with a light, cleaning or replacing fouled spark plugs, replacing ignition components as needed (ignition wires, cap and rotor), and last but not least, adjusting idle speed/idle mixture.
There are different PCV valves for 350 Chevies. You have to make sure you have the right one. If the PCV system is operating correctly, you have a wee bit of vacuum at the hose that is supposed to go into the air cleaner. With that aftermarket air cleaner, it may routed under the air cleaner. Disconnect it and see if the vacuum will hold a piece of paper. If it will not, check the system for leaks. Check the system to see if it is sucking oil. Start with the line from manifold vacuum to the PVC. Is there a lot of oil inside?
Most vacuum leaks on your engine can be found without Carb cleaner or propane. Just disconnect the vac line from the carb and check for vac with your finger. (Manifold vac is present at idle. Vac lines connected above the throttles may have vac when you goose the throttle and not at idle). When you’ve verified vac at the source, reconnect the vac line and check for vac at the other end of the line. If vac is absent or less, the line is leaking.
You may have a leak between the carb and the intake manifold. That looks like an aftermarket aluminum manifold. Does it have a brand name on it? This is big problem area because the fellow who installed aftermarket parts may not have matched parts up correctly. Most aftermarket manifolds accept both kinds of carbs, “spread bore” carbs like the Q-jet as well as “square bore” carbs like the AFB type or Holley. If you have a manifold that accepts both types, it will have 8 bolt holes, for both bolt patterns and you need an Edelbrock adapter plate or you get a big vac leak. You can see if the 4 nuts holding the carb are tight (do not over torque them – the lock nuts should hold them in place).
I think the follow who sold you the Chevy must have had stuff like a power amp, a sub-woofer and maybe a security system hooked up to the switches and wires. I would remove all of that one piece at a time. If you want to install an amp or something later, it will be easier to run new wires and so on than to try to hook stuff up to the “rat’s nest”. In the course of taking that out, you may find something he’s loused up and fix it.
That MSD unit is probably working fine if it’s hooked up right.