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Username Post: 97 1500 4.3 fluctuating idle        (Topic#359215)
Posts: 3

Reg: 11-24-19
12-23-19 11:47 AM - Post#2782753    

While this could be as simple as "replace idle air control valve," I have been deep into this truck doing other things and could use some help in making sure I am on the right track.

This is my first post, btw. It's good to be here. Now a little back story:
The truck shows 459,000 mi but it's on motor and transmission #2. Truth be told, I have run it hard as a daily driver and been religious only on oil changes and air filter. I have caught up to speed on other things recently hich I mention below. As of late, I have also started having hesitation at speed and the heat was not working well. I changed the water pump (it was leaking pretty good) the thermostat, and heater core. After all this, I havent figured out why the idle fluctuates. I'm not sure if the hesitation will be there once driving as I am reluctant to get it on the road as it runs currently. As I stated in the title it fluctuates at idle from 600 to 1100 rpm about every 68 seconds. It usually dies after about 5 or 6 cycles of this but not always then I just set it down. Search changing the water pump it has a squeal sound as well which I cannot really pinpoint in the front if its the fan clutch. I know it's not the alternator power steering and it shouldn't be the water pump but I guess sometimes those can be faulty from the factory.

Other things to note: I have recently checked fuel pressure, replaced the alternator (because the bearings were a little grainy), the EGR valve, temperature sensor (the one by the thermostat housing), plugs, cap, and rotor.

Any guidance is greatly appreciated.

Edited by Aboom on 12-26-19 07:59 AM. Reason for edit: "Fan clutch" got butchered by auto feature

Frequent Contributor
Posts: 1476
Age: 60
Loc: Murphy N.C.
Reg: 01-25-14
12-23-19 06:02 PM - Post#2782786    
    In response to Aboom

Throttle body base gasket blow out is common. Makes for a large vacuum leak.

Posts: 3

Reg: 11-24-19
12-24-19 12:58 AM - Post#2782797    
    In response to junkman104

That's one I havent tackled before. I will hunt down a video of that. Ty.

Senior Moderator
Posts: 29061
Age: 49
Loc: Texas
Reg: 08-01-03
12-24-19 08:43 AM - Post#2782820    
    In response to Aboom

It's a pretty good suspect especially if it's the original gasket. No video needed; it's just the gasket between the TBI and the intake manifold. Pull the TBI bolts and swap out the gasket if it's bad. You can test it with your choice of vacuum leak methods like carb cleaner spray or an unlit propane torch. Take care.


06 Silverado ISS / 06 Silverado SS / 06 300C SRT8

Posts: 205

Reg: 05-01-14
12-24-19 02:37 PM - Post#2782846    
    In response to Aboom

I had irratic idle recently on my '94 4.3L although not as bad as yours and a bit of hesitation when starting off from a standstill.

Replaced the throttle position sensor (TPS) and all is good now.

Posts: 3

Reg: 11-24-19
12-26-19 08:26 AM - Post#2782929    
    In response to Aboom

Thanks you guys. On a broader note...I almost want to throw the towel in on this truck! I say this because of additional issues.I just took a break from the above problem and switched to the front end which needs a lot of work. The lower control arms are touching the rotor having rubbed through the metal guard. The top two arms are different beyond brand. One seems a tad longer. Add to that, the lower arms need bushings replaced and one of those arms looks like it may be bent from a previous lower ball joint pop-off while going 60mph (that was fun and an even funner first time roadside repair in the cold rain!). Shocks need replaced. Springs have 459,000 miles on them so they should probably retire. Then there's the sloppy steering box which I've tightened up several times. Its original and probably needs to go as well. I just need this truck to be reliable enough to get to work after totaling my car hitting a large deer. Only had liability. I'm in between jobs and its holding me back BUT a payment on a newer one is not doable. Apologies for the "vent." Think I will go play with my kid and get back to work on it later all refreshed...thanks again for the responses regarding the idling culprets.

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