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super high idle HELP!

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Old 02-24-2008, 05:25 PM   #1
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Exclamation super high idle HELP!

my uncle has a 95 silverado 4.3 W engine code. when he starts it up it will idle high and continue to idle higher until it reaches around 3000 -3500 rpm. It does not stop even when it warms up. so when he drives it he can't stop because the idle is too high. He replaced the IAC and found no change. Any help?? thinking vacuum leak but not sure where as we can't hear any hissing? thanks
Old 02-24-2008, 09:51 PM   #2
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Re: super high idle HELP!

anyone with ideas?
Old 02-24-2008, 11:58 PM   #3
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Re: super high idle HELP!

could be the Throttle Positioning Sensor(TPS).. is the check engine light on? have AutoZone or another store scan it.. should be free at Autozone and most other places..
Old 02-25-2008, 01:00 AM   #4
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Re: super high idle HELP!

Hey man this could be way out there but.. I just did my IAC about 2 months ago. I started the truck up and it was a super high idle. Now my truck is a 94 so about the same has your dads. I figured out that the male plug had broke and it was able to plug in backwards. I played around a bit with it and found thr right way to plug it in. has worked fine since.
Like I say I might be wrong but that is just my input
Old 02-25-2008, 01:23 AM   #5
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Re: super high idle HELP!

Could very well be a vaccum leak. Get some carb cleaner and start spraying around.

May be the TPS, make shure its not sticking.

Have you checked the timing? Any snags in throttle Cable? Have you adjusted the standard Idle?
Old 02-25-2008, 01:37 AM   #6
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Re: super high idle HELP!

the throttle bodies get worn out and cause idle issues, i would take the tb off and inspect it to make sure its all tight and good. Also it could be the throttle spring is worn.
Old 02-25-2008, 08:17 AM   #7
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Re: super high idle HELP!

Isn't a VIN code W the TPI with the large vortec runners and the ultra expensive fuel injector?

I'd be checking the throttle cable for sticking and even disconnect it to see what happens. Then I'd be checking the TPS as that could be giving a false reading.
Old 02-25-2008, 08:09 PM   #8
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Re: super high idle HELP!

no you are thinking of the CPI which injector assembly was 350 bucks, I use to have one. The code he had was the IAC so he replaced that and it didn't do any good. I will go over sometime this week and look at it to see how everything is. thanks guys.
Old 02-25-2008, 08:52 PM   #9
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Re: super high idle HELP!

Quote: Originally Posted by blazin24
no you are thinking of the CPI which injector assembly was 350 bucks, I use to have one. The code he had was the IAC so he replaced that and it didn't do any good. I will go over sometime this week and look at it to see how everything is. thanks guys.


i bet ya anything its a vaccuum leak, mine was leakin and i dint even kno it and finally the hose broke, it made my transfercase lock up and tore up my tranny at 80mph on the interstate it took me for a ride yea anyways after i put a new tranny and t-case in it still had a high idle and the idle even climbed on its own at times, its prolly a vaccuum leak for sure, follow ur lines and even replace them its cheap to do, and will probably pay off
Old 02-26-2008, 12:58 AM   #10
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Re: super high idle HELP!

I have similar problem, although mine doesn't idle quite as high. I checked the vacuum on it with a vacuum guage and got 17" Hg, not sure what it should be but my 2.5 give 20" Hg. My does throw a map sensor code and tps code though.....

Anyone know the length and diameter of vacuum lines you'd need to replace them all?
Old 03-02-2008, 09:49 PM   #11
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Re: super high idle HELP!

ok i went over today and drove the truck around. We could get it to idle down to normal sometimes by holding the brake in all the way. most of the time it idled just over 1000 rpm. we drove it and if you are driving around 55 -80 if you let off the accelerator and put it in neutral the idle stays up, depending the speed 1500 to 3000 rpm. We sprayed carb cleaner around and nothing! He replaced the IAC and EGR along with PCV and i believe the TPS. We couldn't find any vacuum leaks but we could here something but couldn't tell if it was the serpentine belt or power steering pump or a vacuum leak. there are very few vacuum lines on this truck and its a 2wd. he is going to unhook the batter again to reset the codes and then have them read again. Maybe he got a faulty IAC valve? i don't know
Old 03-03-2008, 02:12 PM   #12
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Re: super high idle HELP!

mine does the exact same thing.... id be interested to know what fixes your problems
Old 03-03-2008, 03:12 PM   #13
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Re: super high idle HELP!

You said he replaced the EGR valve, was this in an attempt to cure the high idle or he replaced the EGR and now it has the high idle? I had a 2.0 SOHC dodge neon that I did a head gasket swap on, when I buttoned it back up and started it I had the high idle, turned out to be that the pipe that came from the exhaust to deliver the spent exhaust to the EGR was not fully connected allowing a major leak...So I would check the EGR connection at both the left side exhaust manifold and the connection at the intake manifold to see if they are snug.
Old 03-03-2008, 03:19 PM   #14
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Re: super high idle HELP!

Stupid high idle. Just glad mine's a manual...
Old 03-03-2008, 11:59 PM   #15
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Re: super high idle HELP!

Quote: Originally Posted by blazin24
ok i went over today and drove the truck around. We could get it to idle down to normal sometimes by holding the brake in all the way. most of the time it idled just over 1000 rpm. we drove it and if you are driving around 55 -80 if you let off the accelerator and put it in neutral the idle stays up, depending the speed 1500 to 3000 rpm. We sprayed carb cleaner around and nothing! He replaced the IAC and EGR along with PCV and i believe the TPS. We couldn't find any vacuum leaks but we could here something but couldn't tell if it was the serpentine belt or power steering pump or a vacuum leak. there are very few vacuum lines on this truck and its a 2wd. he is going to unhook the batter again to reset the codes and then have them read again. Maybe he got a faulty IAC valve? i don't know
Does the vehicle have power brakes? If holding the brake in all the way seems to slow the idle down check the power brake booster for a vacuum leak by disconnecting the vacuum line from the engine & blocking off the connection at the engine. If the idle goes back down to normal the problem is in the brake booster.
Old 03-04-2008, 06:49 PM   #16
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Re: super high idle HELP!

no he replaced the EGR hoping it would help fix the problem. it didn't! he just replaced the MAP sensor with no change, he is going to replace the TPS next, it kinda sucks cauz he is just throwing money into parts hoping it will fix the problem. And only sometimes does pushing on the brake help and that normally only helps if you hold it for over a min when idling. If its driven then pushing on the brake doesn't really help any.
Old 06-14-2008, 10:22 AM   #17
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Re: super high idle HELP!

My 91 S-10 is doing the same thing. It's been running great, but over the past two days I've noticed the idle is VERY high. I checked the throttle cables, oiled all moving parts on it but still idles really high. TPS?
Old 06-14-2008, 11:10 AM   #18
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Old THEAD!

Connect a vacumm gauge to the pass side intake port that feeds the Black Ball and your heat/ac controls.
Vacumm leaks will rise your idle...
Stuck EGR plunger
IAC problems
MAP sensor issues
Coolant temp sensor issues
Leaky injectors
TPS issues
Are common causes for high idle.

When the engine is idling, pull that vacuum line at the front pass side front intake port and your idle should rise, not lower.
Old 06-22-2009, 12:19 PM   #19
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Re: super high idle HELP!

i have a 95 S10, have been doing major work on this truck, changed out the injectors and the valves on the engine(actually my pops is doing it, so if i seem a lil less articulate with cars thats why), anyway we get it to start, but it immediately shoots up to 3000rpms, with no sign of coming down, we checked for vacuum leaks, and almost anything else we can think of, any help?!?
Old 12-17-2009, 03:39 PM   #20
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Re: super high idle HELP!

I am experiencing the same high idle of about 2500 - 3000 rpm.

I have a 1994 z85 4x4 with the 4.3L TBI gas guzzler and an automatic trans. I had just put relays on the headlights so that I can see with them.

I backed out of the garage and let it warm up a bit then went over to the store. The weather is about -28C. Along the way it started to idle at 3000 rpm. (I put it in neutral so that I do not slide into the winter intersections so bad).

I jockey back and forth between neutral and drive so that I can get the shopping done and get home alive. The idle has now dropped to about 2200 - 2500 rpms.

As I pulled into the garage I also noticed that the passenger side floor mat is getting wet with green stuff. 8(

I know what that means but hope that the two are not connected!!

I have checked the vacumn lines and any electrical connectors on the engine but have not found anything obvious.

HELP!!

PS I already used the search which is how I found this thread.
Old 12-17-2009, 09:20 PM   #21
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Re: super high idle HELP!

Check for major vacume leaks. Vacume hoses are always suspect, the TBI base gasket has been known to leak, the green stuff in the pass floor is the heater core - unrelated issue. So you have 2 problems, good luck.
Old 03-18-2010, 04:19 AM   #22
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Re: super high idle HELP!

my 94 with tbi does this too i know it cant be good for the tranny iv replaced the iac and tps twice and the only thing that helps is to take it out and squirt it down with cleaner and put it back in idles normally everytime..last time it decided to do this i was up on an alignment rack...not good
Old 04-26-2010, 09:41 PM   #23
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Re: super high idle HELP!

I have been having the same problem. I replaced the throttle body gasket and it help a whole lot. Still just a little high for me, but a big difference.
Old 02-01-2012, 09:38 PM   #24
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Re: Old THEAD!

Quote: Originally Posted by Bill Wheats
Connect a vacumm gauge to the pass side intake port that feeds the Black Ball and your heat/ac controls.
Vacumm leaks will rise your idle...
Stuck EGR plunger
IAC problems
MAP sensor issues
Coolant temp sensor issues
Leaky injectors
TPS issues
Are common causes for high idle.

When the engine is idling, pull that vacuum line at the front pass side front intake port and your idle should rise, not lower.
the vac gauge is to check 4 vac leaks??n if u pull the pasanger vac line off the intkae n it lowers what does that mean..vac leak??
Old 02-02-2012, 05:48 AM   #25
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Re: super high idle HELP!

definitely find where the air is getting into the engine allowing it to rev so high. Vacuum, severe intake leak, IAC pintle not seating all the way.

I'd pull the IAC wires off while its running that high, turn it off and see if the IAC pintle is opened a lot. If it's closed, there is most likely a physical leak somewhere
Old 02-08-2012, 08:21 PM   #26
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Re: super high idle HELP!

interested as well...91' s10 blazer 2 door tbi 4.3/700r4 same issues, very hard to stop the truck and almost seems like stuck in cruise control.
Old 04-25-2012, 04:04 PM   #27
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Re: super high idle HELP!

Quote: Originally Posted by techbot
My 91 S-10 is doing the same thing. It's been running great, but over the past two days I've noticed the idle is VERY high. I checked the throttle cables, oiled all moving parts on it but still idles really high. TPS?

Mine did the same thing after replacing the TPS, It turns out the pre heater flex tube that connects to air intake tube to the exhaust manfold had not been connected, I replaced it because it denigrated in my hand, That solved my high idle issue
Old 07-10-2012, 05:46 PM   #28
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Re: super high idle HELP!

dur.. someone mentioned my thought.. I suspect Brake Booster... like old s-10 owner
that hose is almost 1/2". any of the other hoses leaking except the carbon filter vaccum lines will make the motor run badly, if at all. The brake booster or its line leaking will make it idle high and probably throw a code because the motor has no idea why that much air is getting into the system. disconnect the hose and block it.. if it fixes the problem you have found your issue..
Old 05-05-2013, 05:41 PM   #29
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Re: super high idle HELP!

I have a 97 s10 W
love the truck, but omg this s driving me crazy like so may others, found this thread along with more, but im still at the stage where im just changing parts hoping itll fix it.
bout to sell my SS and just go buy something newer/bigger.
Old 11-13-2013, 10:51 AM   #30
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Re: super high idle HELP!

I have the same issue.... MOST of the time its fine. but some times it idles high.. as high as 2500. 97 v5 5spd..... being intermittant, drives me nuts.. have not thrown any parts at it yet. Ive assumed it is some sort of vac leak... did a search on EGR valve.. they mostly say if it is an issue, it will not idle... will cut off. Mine never cuts off. and so far, it always slows down back to normal in a few moments when I stop. but some times going down the road, I can run 45 mph in 5th with out my foot on the gas.... aaaarrrrrrggggg. should have bought a prius...

WHAT HAVE PEOPLE DONE that fixed this?????? Agrevating thing about forums is few folks come back and Say What they did that fixed the issue they were asking about....
Old 11-13-2013, 01:55 PM   #31
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Re: super high idle HELP!

Quote: Originally Posted by cobraearl
I have the same issue.... MOST of the time its fine. but some times it idles high.. as high as 2500. 97 v5 5spd..... being intermittant, drives me nuts.. have not thrown any parts at it yet. Ive assumed it is some sort of vac leak... did a search on EGR valve.. they mostly say if it is an issue, it will not idle... will cut off. Mine never cuts off. and so far, it always slows down back to normal in a few moments when I stop. but some times going down the road, I can run 45 mph in 5th with out my foot on the gas.... aaaarrrrrrggggg. should have bought a prius...

WHAT HAVE PEOPLE DONE that fixed this?????? Agrevating thing about forums is few folks come back and Say What they did that fixed the issue they were asking about....
Check that the throttle plate is closing all the way
Check the throttle linkage is not binding
Check for vacuum leaks
Check the IAC
Check the TPS
Check EGR
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