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Diagnosing stalling at startup/engine bogging

AjBranson99

AjBranson99

Not-quite-so-new-guy
Jul 26, 2024
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So as the title suggests, I am trying to figure out what exactly is going on with my Monte. It's the 1985 Monte Carlo with the 4.3l v6 tbi. The issues I'm running into are always at startup after the car has been sitting for a few hours or more. Whenever I start it after its been sitting, the engine will either idle really low stall or attempt to stall if I don't give it some gas, or will idle pretty high. (most of the time it idles low, I'd say that it idles high maybe 1/5th of the time) The other problem I have is within the first 5-10 minutes of driving, the engine will bog when I try to give it power while getting onto the highway. I don't floor it or anything, I try to be pretty gentile with this thing. I should add that the car was the lowest trim model you could get at the time, so the tach gauge doesn't have a needle or anything for me to actually read the rpms to see how low/high they get, but I would guess that when it idles high it is somewhere between 1000/1500 rpm. So far I have only replaced the fuel filter, and while that did help with the engine feeling more responsive after its been driven a bit, the problems I mentioned are still popping up. I am unsure of what I should look at next to solve these issues, and any help would be greatly appreciated!
 
AjBranson99 said:
So as the title suggests, I am trying to figure out what exactly is going on with my Monte. It's the 1985 Monte Carlo with the 4.3l v6 tbi. The issues I'm running into are always at startup after the car has been sitting for a few hours or more. Whenever I start it after its been sitting, the engine will either idle really low stall or attempt to stall if I don't give it some gas, or will idle pretty high. (most of the time it idles low, I'd say that it idles high maybe 1/5th of the time) The other problem I have is within the first 5-10 minutes of driving, the engine will bog when I try to give it power while getting onto the highway. I don't floor it or anything, I try to be pretty gentile with this thing. I should add that the car was the lowest trim model you could get at the time, so the tach gauge doesn't have a needle or anything for me to actually read the rpms to see how low/high they get, but I would guess that when it idles high it is somewhere between 1000/1500 rpm. So far I have only replaced the fuel filter, and while that did help with the engine feeling more responsive after its been driven a bit, the problems I mentioned are still popping up. I am unsure of what I should look at next to solve these issues, and any help would be greatly appreciated!
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I would start by lubricating the throttle shaft both side with real oil even black used oil ,also your going to need to check fuel pump pressure fuel filter and any maf sensor if it has one know your plugs condition ! and read what that indicates ect ?. Ect .If your ignition wires are 9 years old ? Get new ones"
 
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I worked on these when new. It is OBD1 system. Look up on internet the basics of the OBD1 system, this will give you a little idea of how everything works.

Get a new O2 sensor, unplug the current one and plug in the new one. Zip tie it to something under the hood where it is out of the way and wont get hot or damaged. Doing this puts it "open loop" and not "Limpy". Go for a test drive, notice any changes and report back.
 
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Is your CHECK ENGINE LIGHT (CEL) working? Key on, engine off make sure that it lights up, then after starting it goes out.

If it doesn't light up, you may have a problem with the bulb, dash cluster, wiring or lamp driver. You want to be sure that CEL works because it's your first clue if there is something going on with the ECM and Engine Control/EFI/TBI system.

Here's some info from the Resources section of this site on the CEL and related components if you need.
Resource icon GP403

That Mystery Check Engine Light- Lamp Driver Repair Information For CCC Cars

If you have a CCC G-body car, you have this. From what I understand, it takes a 5V signal....

If it's not working, you can't do the simple ALDL jumper and count light flashes for any stored codes and you'll need a code scanner for OBD1 which are not very common anymore. If it's working, fine and goes out when you start the car then that means at least there isn't an active fault code but there still might be a history one stored that if you can get with scan tool might help point in the right direction.

If all of the CEL is all ok, then you're gonna have to do the basic troubleshooting using some of the links above from prior post(s), as it could be fuel, air or spark related.

Does the car sit unused for long periods?
 
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Rereading your initial post I was thinking carburator... You have TBI. Pull your IAC valve and clean it with spray cleaner, or replace it. All the items you mention is directly related and can be caused by the IAC. It gets carboned up and starts to stick... Can't control the idle air volume that the engines needs.

Dies at stop light shortly after starting, inconsistent idle, idles fast, idles slow, stalls with light acceleration, difficult to tune. Replace cap, rotor, coil, wires, plugs yet no change. Change fuel filter... No change. Check FP pressure, but it's fine....

Check the IAC
 
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spongbob said:
I would start by lubricating the throttle shaft both side with real oil even black used oil ,also your going to need to check fuel pump pressure fuel filter and any maf sensor if it has one know your plugs condition ! and read what that indicates ect ?. Ect .If your ignition wires are 9 years old ? Get new ones"
Click to expand...
I should of said map sensor and hose also CCM temperature sensor and plug connections ? Drive it around the block then take a spark plug out and take a picture of it the nose insulator then upload it here please ( spark plug)if you find an old van with a 4.3 ect same size motor close year you can switch the brain out whatever different brains sometimes are stronger"! plus its going to tell you if the electrolyte capacitors have leaked and you need a cpu ( brain) some parts salvage yards will let you try it there '... I suppose there's one on ebay but not out of the question if you clear that up you may be looking at swopping injector ( tbi. ) or something what shape is your catalytic converter ? Need to know (plugged up?)
 
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