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turkeyshooter
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Aug 26, 2012, 12:04 PM
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I just bought an older 1988 Chevy Silverado PU Truck & the engine idle is way high. Makes it hard to put in gear. I am afraid I will damage transmission attempting to get it in gear. It has a 350 Chevy engine in it I believe. It is a Silverado 4x4. The fellow told me he believed it might be the throttle body sensor. I don't know where that is at. I cannot find any idle adjustment screw on the carb. Any help will be greatly appreciated. Thanks in advance.
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Tom Greenleaf
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Aug 26, 2012, 2:15 PM
Post #2 of 26
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Re: High Engine Idle
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I don't think any 88 5.7 or any had a carb. Check for vacuum leaks, and just plain look into throttle body and then clean it. Is the throttle plate loose in there somehow or can't return to its home position? You really don't adjust idle speed on those at all,
T
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Hammer Time
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Aug 26, 2012, 2:56 PM
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Re: High Engine Idle
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It's fuel injected. It has no carb and it has no idle adjustment. Look for any vacuum leaks, binding linkage or faulty temp or TPS sensors.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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turkeyshooter
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Aug 27, 2012, 6:07 AM
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Re: High Engine Idle
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 ere. & get back to you. I appreciate the help. Thanks.
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turkeyshooter
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Aug 27, 2012, 6:52 AM
Post #5 of 26
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Re: High Engine Idle
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I do notice the guy had installed an extra temp gauge. What to do if the TPS sensors are giving a false reading & where are they located? Thanks,
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Tom Greenleaf
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Aug 27, 2012, 7:23 AM
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Re: High Engine Idle
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Not going on a goose chase yet but check for vacuum leaks as said. Coolant temp sensor (CTS) is right at thermostat (usually) with black and yellow wire usually.
Throttle position sensor (TPS) is located/mounted such that it physically senses the movement of the throttle plate's pivot.
Aftermarket temp gauge? Why? If that is wiring into an existing one could confuse this thing.
Codes are primitive in '88 and not going there yet but you just count blinks of CEL - not yet IMO as I don't know what has been done to what.
For now I'd just physically take off intake parts and look for anything vacuum hosing and that throttle plate moves and returns freely and properly by hand underhood.
Begin there,
T
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Hammer Time
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Aug 27, 2012, 7:29 AM
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Re: High Engine Idle
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You'll need an OBD1 scan tool to see the temp sensor data. Check it when dead cold and compare readings between the coolant temp sensor and the Intake air temp sensor and they should be equal.
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turkeyshooter
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Aug 27, 2012, 8:11 AM
Post #8 of 26
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Re: High Engine Idle
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I could not find any vacuum leaks. Not sure why he installed the aftermarket sensor. The throttle body seems to open & close freely although its a bit tight. It does close completely. The fellow that sold me the truck seemed to think it needed a new TPS. I will have someone check those readings. Thanks,
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turkeyshooter
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Aug 28, 2012, 4:48 PM
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Re: High Engine Idle
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A neighbor suggested I check for a vacuum leak between the throttle body & manifold. He said that was a common problem with that model chevy. How would be the best way to check for a leak there? Is there some kind of spray that I could spray at the area that would temp seal the leak enough to idle down the engine for a sec to determine if there is a leak there?
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Discretesignals
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Aug 28, 2012, 5:02 PM
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Re: High Engine Idle
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Get a spray bottle with water. Set it so it sprays a stream. Spray around the base of the throttle body with the engine running. You'll hear the water getting sucked in if there is a leak. With the engine turned off you can fully open the throttle and look down inside the throttle body bore with a flashlight. Sometimes you can see part of a gasket that got sucked in too.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Aug 28, 2012, 5:03 PM)
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turkeyshooter
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Aug 28, 2012, 5:05 PM
Post #11 of 26
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Re: High Engine Idle
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Thanks I will give that a try!
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turkeyshooter
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Aug 28, 2012, 5:52 PM
Post #12 of 26
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Re: High Engine Idle
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I could not see any gasket. What does the sound, sound like of the water being sucked in. I think I noticed a slight lowering of the idle when spraying the water, but not much.
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Discretesignals
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Aug 28, 2012, 5:58 PM
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Re: High Engine Idle
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Skip to around 8min30secs.
http://www.youtube.com/...5Q4&feature=plcp
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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turkeyshooter
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Aug 29, 2012, 9:25 AM
Post #14 of 26
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Re: High Engine Idle
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Thanks for that video. I could not find a vacuum leak. I ended up taking the throttle body off the manifold, checking the gasket (it was fine), and cleaning the throttle body. Still no change. Idling is still really high. In the process I did find a green wire with a slotted connector on the end that is not connected to anything, and I cannot find a place for it to connect up to. It does look like it might have been connected to a sensor on the block (looks like an oil pressure sensor) that has been replaced with another thicker wire that goes directly into that sensor. Any ideas on that green wire? I was wondering if I replaced the CTS next to the water outlet if that sensor might be causing a problem? There is one vacuum line that is plugged coming out of the front of the throttle body that went somewhere towards the right side (facing) of the engine.
One more question: How do I check for the faulty TPS & CTS?
(This post was edited by turkeyshooter on Aug 29, 2012, 10:00 AM)
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turkeyshooter
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Aug 29, 2012, 10:05 AM
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Re: High Engine Idle
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To Hammer TIme: Where is the Air Intake Sensor located on this 88 Chevy? May sound like a stupid question as I am assuming somewhere around the intake, but It won't be the first time I got messed up with the assuming something. Know where the word comes from. What do I know, I am still looking for points! By the way getting close to that area, could it be the timing is off? Truck starts pretty good though & it seems like if the timing were off it would not start easily.
(This post was edited by turkeyshooter on Aug 29, 2012, 10:12 AM)
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Hammer Time
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Aug 29, 2012, 10:15 AM
Post #16 of 26
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Re: High Engine Idle
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After looking it appears that they didn't use one on that engine.
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turkeyshooter
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Aug 29, 2012, 10:18 AM
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Re: High Engine Idle
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Thanks, any thoughts on the timing being out?
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Hammer Time
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Aug 29, 2012, 11:31 AM
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How would I know that? Grab a timing light and check it.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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turkeyshooter
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Aug 29, 2012, 1:21 PM
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Re: High Engine Idle
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Perhaps I worded that wrong. Sorry, I really do appreciate all the help. What I really meant to say was could the timing being off be a possibility in your mind. Would it be something you would check in this process of looking for a high idle problem. Most seem to think its a definite vacuum leak somewhere on the throttle body or between the throttle body & manifold( which I have already eliminated.) I know us rookies tend to hit a nerve. My apologies and thanks again.
The OBD1 Test showed codes 12, 22 & 24 Then it basically started all over again.
(This post was edited by turkeyshooter on Aug 29, 2012, 2:12 PM)
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Hammer Time
Ultimate Carjunky
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Aug 29, 2012, 3:05 PM
Post #20 of 26
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Re: High Engine Idle
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Timing is something you should be just automatically checking. Follow the procedure. Idle speed is controlled by metering small amounts of air through the throttle body. Unmetered air leaking in somewhere is the most common cause of idle issues. A good tech would be analyzing the sensor data to look for what is going on.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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turkeyshooter
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Aug 29, 2012, 4:01 PM
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Re: High Engine Idle
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Thanks for the lesson. Its not been to a real tech yet. Just this country boy trying to save a few bucks. I appreciate the info. I concentrated on spraying some throttle body spray on the area of the injectors where there is a smaller gasket and did notice an idle down for a few seconds then it went back up. I think I need to buy that rebuild kit with the gaskets for those injectors. I installed a new TPS with no change just previous to doing that test. Thanks Again.
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Hammer Time
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Aug 29, 2012, 4:37 PM
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We fill the system with smoke to locate the leaks but you may have found them.
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turkeyshooter
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Aug 31, 2012, 6:21 AM
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Re: High Engine Idle
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One code shows a fault in the VSS Vehicle Speed Sensor, does anyone know where that is located? Thanks in advance.
(This post was edited by turkeyshooter on Aug 31, 2012, 6:27 AM)
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Hammer Time
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Aug 31, 2012, 7:04 AM
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The VSS is in the transmission tailshaft.
I didn';t read this all over again but what did you do about the code 22 (TPS)?
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
(This post was edited by Hammer Time on Aug 31, 2012, 7:14 AM)
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turkeyshooter
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Aug 31, 2012, 7:29 AM
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Re: High Engine Idle
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Replaced the TPS
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