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93 Chevy Pickup High Idle
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dlcarp
Novice
Jan 9, 2013, 9:42 AM
Post #1 of 6
(21789 views)
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93 Chevy Pickup High Idle
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I have a 1993 Chevy 1/2ton pickup 2wd with a 5.7l engine with tbi.
The engine has started to idle very high.
I have replaced the idle control valve/soleniod but this didn't make a difference.
I'm open for any help and suggestions
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 9, 2013, 10:33 AM
Post #2 of 6
(21772 views)
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Re: 93 Chevy Pickup High Idle
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Some ideas and checks:
*Vacuum leaks? Check for any.
*Does throttle cable freely allow throttle plate to close fully or can you push on it and it can close more? No harm in cleaning (carb cleaner) the throttle body either.
* How high is high? Just a bit or way beyond reasonable? Not sure if you have an RPM reading on dash for '93.
* Does it run properly otherwise? If so my guess is vacuum leak issues, throttle plate or cable(s) attached.
* Not always too helpful pre OBDII but a code reading could help.
* One more slight chance is 'gas pedal' inside which should have a cable thru firewall is obstructed, frayed anywhere there or underhood. Floor mats or anything in the way there?
Just some things that can happen of several,
T
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dlcarp
Novice
Jan 10, 2013, 8:00 AM
Post #3 of 6
(21730 views)
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Re: 93 Chevy Pickup High Idle
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There is no codes, vacuum leaks, cable or throttle hang ups.
The TBI was completely cleaned 3 months ago.
I don't know exactly the rpm difference but you can tell at idle and when you put in gear. It hits hard when you change gears.
It runs ok other then that.
I have noticed that when the weather is warm it idles just fine.
Could it be the map sensor?
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 10, 2013, 8:22 AM
Post #4 of 6
(21724 views)
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Re: 93 Chevy Pickup High Idle
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Hmmm? '93 you have me thinking harder as things changed that year for some things. The key here is weather being warm all seems normal and not sure how you verified no vacuum leaks.
For now some questions:
* What do you call warmer weather?
* Are you using A/C or Defroster/Defog setting that coincides with this?
* Cleaning throttle body doesn't mean it's perfect but doubting that for now.
** MAP is sensing "manifold actual pressure" meaning vacuum and you could see with a "T" if it get the actual manifold vacuum reading.
** There's an engine coolant temperature sensor near thermostat that may think engine is too cold for too long. They aren't that common to me to go wrong without wild problems not just idle speed.
** There may be incoming air temp sensor(s) in the path of incoming air. Not sure if vacuum or electric on this. If vacuum follow that hose to a vacuum tree which I don't think this has but report if it does.
* Does engine stay at a steady temp on gauge. It should be rock steady once warmed up w no notable changes where needle sits. If not that is a clue.
Integrity of all air intake parts start to housing connecting to throttle body must be in good shape - no leaks along the way or cracks in anything.
One last for now - Does the exhaust smell funny or rich at all if your nose is good? Good grief just a quick nearby sniff don't be breathing that.
Now stuck on things that the temp of weather could cause a change that wouldn't set a code?
T
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dlcarp
Novice
Jan 10, 2013, 10:07 AM
Post #5 of 6
(21713 views)
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Re: 93 Chevy Pickup High Idle
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What I'm meaning by weather change is its about 30degrees warmer now then hat it had been. It was in the 20-30 degrees and now its up to 50-60 degree weather.
Not using the a/c or defroster.
The engine temperature gauge hasn't been steady lately.
Fuel economy has dropped.
Exhaust does smell funny and smells a little rich.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 10, 2013, 11:55 AM
Post #6 of 6
(21702 views)
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Re: 93 Chevy Pickup High Idle
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Anything that causes an engine to not run its best will drop fuel mileage. We (many places) have that damn ethanol in the gas that doesn't give the MPG or HP of real gas for vehicles not specifically designed to deal with it. It does mess with gaskets, hoses and anything it touches on engines made even a few years ago never mind this.
Still the temp gauge not staying steady is probably the biggest problem right now. Even @ 50-60F out this shouldn't struggle to stay steady with a weak fan clutch (probably NG now) but if pulling air even fairly well that could probably wait.
Flush out cooling system now and new quality correct thermostat just because. Note what junk you can see coming out, and look (near sure you can) right into radiator to see if it is blocked or starting to clog too. Do NOT exceed a 50/50 mix which = protection to -34F as ability to cool is reduced!
The ETS or CTS could be getting fooled or really be bad sending info of wrong actual engine temps which even in '93 adjusted how much fuel to deliver and no doubt if it thought colder would raise the idle on purpose. They can be tested out measuring OHM @ a given temp but I think just a $20ish buck item I'd toss it and carefully check the plug too. Pigtail is available is that is a mess. It may not throw codes for you for that alone but probably will soon if you are smelling exhaust not being normal or rich.
I think this truck isn't getting the right info on what temp it really is but actual engine temp fluctuating is a clear sign something isn't right about the plain cooling system.
You need this even if not the problem then I'd be concerned that the throttle plate isn't right or something in there but not sure why the temp outside matters as already said.
Side note on this joint: I'm not here all the time but a lot. Others will jump in with their ideas and hope they do. Been at this a while and it's still tough do diagnose out everything on the web vs being right there for something without a code or a host of other tests or observations that would catch out eyes if it was right in front of us.
Keep at it,
Tom
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