k5 high idle

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kwbush
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Joined: Sun Jun 08, 2014 5:42 pm

1995 c-2500 2 wd 5.7 l auto high idle, bangs into gear

Unread post by kwbush » Sun Jun 08, 2014 6:24 pm

:oops: Got a 1995 Silverado whose service engine soon lite just came on. Along with the lite came an increase in engine idle speed (600 rpm to 1200 rpm) and the automatic tranny bangs into gear so hard it pushes me back in the seat. The other gear shifts are progressively gentler but still harder than normal. Online I was told the shifting problem was caused by a faulty TPS (throttle position solenoid) which I changed but all remains the same.

Any advice as to what to try next?

1995 Silverado 5.7 l, automatic, 2-wd, C-2500 has a set of headers and a towing cam, can't seem to locate an O2 sensor but the truck, until last week, ran perfectly fine.

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carriedi
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Joined: Wed Apr 10, 2013 12:42 pm
Location: Oregon

Re: 1995 c-2500 2 wd 5.7 l auto high idle, bangs into gear

Unread post by carriedi » Sun Jun 08, 2014 9:13 pm

you're going to need to scan the computer for the code. when the service engine soon (SES) light comes on a code is usually stored in the computers memory. Most cars or trucks will run differently when the SES light is on. It runs differently because instead of using the inputs the computer usually sees to make everything run normal it will put in a substitute value for the input that it sees as not being right. Of course the value it makes up is not really correct, it is just a value to keep the engine running so you don't get stranded on the road somewhere. So, scan for the code and start from there.

as for the symptom, higher than normal idle, can be a few things. when you scan for codes look at your fuel trims, your O2 sensor and your idle air control (IAC). you could have a vacuum leak that will make the computer add fuel to keep the O2 sensor happy. (which means the idle will go higher because more air and more fuel)

Do you know what the code is for the check engine light?
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ddafternoons
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Joined: Sat Jun 14, 2014 8:24 am

k5 high idle

Unread post by ddafternoons » Sat Jun 14, 2014 8:47 am

Hello. I'm having a problem with my son's 1988 350 tbi k5 blazer. It won't go into closed loop. It's idle is too high all the time. We changed the coolant temp. sensor, no difference. Checked the timing, but I knew it wouldn't be the problem, unless it was so far out of spec. that it could be the cause. Timing is not quiet on zero, but this, in my humble opinion, is probably due to the idle problem. I tried to put my dist. wrench on the darn hold down bold but it wouldn't budge. The car had no cat. converter on it when we bought it and it was throwing a code for the egr. I installed, what I believe is a Cal. approved converter on it and the code went away. I'm not sure why it say's it's a 3-way cat. when I don't see a air tube at the cat. I always thought a 3-way is supposed to have an air tube at the cat. I did find a hose hanging down from the back side of the engine and I can't seem to see where it's coming from. I've never seen a hose, it's around 5/16" hosing, hanging off a engine that serves no purpose. I pulled the IAC unit, started up the car and put my finger in the hole where the IAC was and the idle dropped. So I figured that the IAC motor wasn't working. Put a new one in and it seemed to run faster. I don't know if I was to do something to introduce the new IAC into the system. I don't show any codes. I sprayed for vaccum leaks and I haven't found any obvious problems. So I was desperate and turned down the throttle screw on the throttle body, even though I know this isn't the correct thing to do, just curious, but it idled down a little but not the answer. I'm not sure if the O2 would help, I haven't checked it, but I would thing if it's not operating properly a code should pop up. I'm not sure if the MAP would cause this problem, but I don't want to shotgun the problem only to find out I'm just guessing and buying parts for the sake of it, hoping it will fix the problem. I will attempt to clean up the ground wire area where the coolant temp sensors grounds but it doesn't look like it's very corroded. Help!!

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carriedi
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Joined: Wed Apr 10, 2013 12:42 pm
Location: Oregon

Re: k5 high idle

Unread post by carriedi » Sat Jun 14, 2014 6:20 pm

I think you should have your truck scanned. you need to see the data stream so you can see what the computer is doing. If you have a vacuum leak of if you have too much fuel in the mix your computer will react to the oxygen sensor and try to make it run clean. (emission wise) Look at the fuel trims and coolant readings. Look at the IAC count. The computer is supposed to control your idle. Find out why it is keeping it so high.

without seeing what the computer is doing, everything is just the shotgun approach. So, depending on how much ammo (money for parts) you want to spend, you could narrow your search by having it scanned.

scanning will tell you the coolant temp status, oxygen sensor responsiveness, iac counts, fuel trims, etc.
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