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My 4.3 idles too high

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Old 03-17-2004, 01:51 PM   #1
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My 4.3 idles too high

My truck is pretty much stock, except for a cone replacement filter for my stock airbox. Anyways, i've noticed that it's starting to idle much higher that it has in the past. Is the fix as simple as putting in new plugs and getting the timing adjusted? I have already bought new plugs but not installed them yet, however, could it also be somthing like a coil?
Old 03-17-2004, 04:41 PM   #2
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Re: My 4.3 idles too high

it might be because the weather is really cold.....if the engine is cold it will idle higher when you start it....when it warms up the idle rpm should go down...if not im not sure what the problem is....next time you start it...let it sit for a few minutes maybe 5-10 and then comeback and check to see if it idles lower
Old 03-17-2004, 04:47 PM   #3
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Re: My 4.3 idles too high

Somewhere I read that if alternator isn't putting out enough, the vehicle will raise its idle to compensate (to produce more amperage). It was in a post somewhere... someone might want to verify that that does happen though. It could possibly be that, though. Alternators are another one of those things that just go out on our trucks. Generally it is a bearing siezure or the diodes going poof.

Also, you may want to just try resetting your ECM. It might have just gotten some goofy reading and decided to compensate by raising the idle. Unhook your battery and let it sit for about 30 minutes or so. That should clear it out.
Old 03-18-2004, 09:32 AM   #4
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Re: My 4.3 idles too high

Thanks guys! Well I know it's not just because it's cold, it's just one of those strange things that strted happening all the sudden. But you mentioned the alternator... i'm wondering if that could be it because it is just the stock alternator. I have a bunch of stuff pulling juice... Clarion MP3 deck, Kenwood Sirus reciever, radar detector, cell charger, amp, sub, higher wattage bulbs. That may be it!!! Thanks man, i'll look into that more.

If I do find that may be it, what should I get to replace the stock one????

Thanks again!
Old 03-18-2004, 09:37 AM   #5
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Re: My 4.3 idles too high

Aha! You asked the right person for the alternator I have a 180 amp one. It was really good priced. Ran about $140 I think.

You can get some great stuff at Alterstart -- http://www.4alterstart.com.

They're great people and have lifetime warranty on the stuff and more. My 180amp has a 200amp heavy duty diode package so it takes a helluva lot more to burn that out. Plus the bearings are by NTN so they supposedly seal better and don't get brush dust in them (and eventually sieze) like the stock bearings do. You'll have to upgrade the charge strap to a 4-gauge or larger cable. Stock is 8 gauge and is flimsy. You'll burn up the cable if you don't upgrade it... it costs like $5-7 at any auto store for a 24" one to fit the alternator and battery.

I run an Alpine 4x50watt head, PPI PCX-480 (480watt) amp, 2 10" Kicker subs, Clarion 6.5" in the doors, Clarion 4x6" in the rear, and a coustic XM3 crossover. Plus some Hella 2020 (combo fog/driving lights) and more. Hate having not enough juice...

That may not be the reason its idling higher but it is something to check into. Can't remember where I read about the alternator and ECM and idling but a couple people had agreed with it.

Just ran into this...

[If idle speed is out of range, the computercommands the IAC valve to either increase ordecrease the bypass air flow. Additional sensorinputs from the coolant sensor, brake switch andvehicle speed sensor may also be used to adjust idlespeed according to various operating conditions.Idle speed may also be increased when the A/Ccompressor is engaged, the alternator is chargingabove a certain voltage, the automatic transmissionis in gear, or power steering loads are high]

Hopefully that has something you can use...
I'd try resetting the ECM also. That may fix you right up.

BTW, I blew my stock diodes out. My bearings were already whining though so it was going either way. I lived and learned, bought a capacitor for the system, and a bigger alternator, and have never looked back.

Last edited by nater006; 03-18-2004 at 09:42 AM.
Old 03-18-2004, 09:55 AM   #6
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Re: My 4.3 idles too high

Thanks nater! I'm going to reset the ECM today and see if that helps. I may take it somewhere like Autozone or somthing and have them hook somthing up to alternator and check the draw on it. But if resetting the ECM doesn't work, I will go with a HO alternator.

Thanks again Nater!!!
Old 03-18-2004, 10:39 AM   #7
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Re: My 4.3 idles too high

Have you considered a vaccum leak? When you did your intake, did you plug your air temp sensor back in? What's your idle at rpm wise? It's not likely that the alternator would be causing that... What year is your truck? Could also be your IAC is dirty... You might want to consider pulling the IAC and cleaning it (carb cleaner and a wire brush)
Old 03-19-2004, 12:01 PM   #8
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Re: My 4.3 idles too high

It's a 1998. I actually reset the ECM yesterday and it may have cleared it up at this point. It ast for 3 hours, so it was plenty cold here in Michigan. When I started it, it went right to to about 500-600 rpm. When before, it was closer to 900-1000. It was just really strange because a couple of different times, I could "idle" down a flat road at 25mph, without even touching the gas pedal. I was just baffled at that! I figured i was just a sensor or somthing stupid that I wasn't thinking about. And like I said, resetting the ECM seems to have taken care of it. But I am still considering a new alternator...


Thanks all!!!
Old 03-19-2004, 12:10 PM   #9
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Re: My 4.3 idles too high

I had the same problem. Except, you didnt say whether the engine was hot or cold. I have a 97 4.3L and it help high idle at all times, whether the engine was cold or hot. I had to take it to the local shop and they told me that this happens to alot of the 4.3L that was put into the s10's. They had to reset my computer. I dont know why, but my problem was the computer, once they reset it, everything worked fine and 8 months later, I still havent had any problem.
Old 03-19-2004, 12:30 PM   #10
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Re: My 4.3 idles too high

Good, glad the reset fixed it.

If you aren't having any charging problems currently you may not need to upgrade your alternator. I upgraded mine when my old one failed. If yours isn't having any charging problems, you probably will want to save the money. Though, when it does go out, a 140, 180, or 200 amp alternator is a good drop-in replacement.
Old 03-19-2004, 12:34 PM   #11
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Re: My 4.3 idles too high

Oh yeah.. BigCat24...

My alternator died and my truck ignition finally gave out when I was heading north on Harrison Rd there in East Lansing, right where it hits Shaw Lane. Desperately trying to make it to a parking lot where I could legally park or the parking garage at Kellogg.. ended up dying at about 20mph right as I was approaching a red light at that intersection. Jumped the curb and parked it in the median Traffic was heavy anyway. A cop finally went by and stopped... he asked if I was drinking and hit something...haha. Seemed appreciative of me not blocking traffic. The tow truck guy was a little less appreciative, trying to hoist it up in the snow
Old 03-19-2004, 04:21 PM   #12
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Re: My 4.3 idles too high

Clean your IAC.

Last edited by BlazerLT; 03-19-2004 at 04:21 PM.
Old 03-19-2004, 05:21 PM   #13
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Re: My 4.3 idles too high

Check all your vacuum lines. I bought my 92' Blazer from a person who said it didn't run. Got it home, popped a battery in, fixed a fuel line and fired it up. Ran like crap so I changed plugs, made a little difference but not much. Finally found the vacuum line from the distributor to the manifold had laid on the exhaust manifold and burnt thru and another line that was brittle. Replaced them both and now it runs fine.
Old 03-19-2004, 07:52 PM   #14
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Re: My 4.3 idles too high

Love finds like that.

One mans garbadge is another man's gold.
Old 03-19-2004, 11:34 PM   #15
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Re: My 4.3 idles too high

Quote: Originally Posted by BlazerLT
Clean your IAC.
i'll second that notion
Old 04-15-2011, 02:51 PM   #16
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Re: My 4.3 idles too high

Ok I'm wondering about this and I will check a lot of things out, my daughter has a 98 s-10 w/ 4.3 and the charging needle goes down considerably when you step on the gas and raise the idle, even enough to make the dash lights dim as well. I will try resetting the computer after I look for vacuum hoses melted, and see what happens but right now when you hit the gas, the needle moves way down toward discharge and appears to be about 10 or 11 volts, I'm guessing it should read at about 14 when you raise the idle and not when you drop the idle. As I turn the heater on, lights on, it still tends to drop when you raise the idle and go towards charging when you reduce the idle... I'll report back with what I find...
Old 04-15-2011, 08:56 PM   #17
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Re: My 4.3 idles too high

Ok so I found a spark plug wire that was grounding out on the transmission filler tube... I also tried another battery same results, then I did unhook the battery while it was running and it died right away so I'm thinking the voltage regulator inside the alternator is bad... So I'll try a different alternator I'll report back with the results I find...
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