98 Chevy Silverado Idle problem, Does Not Idle well, until warmered up

[oregon712]

98 Chevy Silverado K3500 7.4L. i'm still looking for answers on my idle problem. When cold or sitting for a while, she idles (lobing, i guess) and tries to die(recover most of the time by reving up to 1000rpm), when it tries to back down from 1000 rpm. she runs great once warmed up, but when cold does not idle. Any Ideas? Thanks, Sean

[Mr. Smith]

Originally Posted by oregon712

98 Chevy Silverado K3500 7.4L. i'm still looking for answers on my idle problem. When cold or sitting for a while, she idles (lobing, i guess) and tries to die(recover most of the time by reving up to 1000rpm), when it tries to back down from 1000 rpm. she runs great once warmed up, but when cold does not idle. Any Ideas? Thanks, Sean

Could be the temp sending unit for the computer. It doesn't tell the computer the engine is cold and give it a bit more fuel. Just like a choke.

[dr olds]

it is not the temp send unit you need it is the coolant temp sensor. the temp sending unit is for the guage, the coolant temp sensor is for the computer. .... you may want to look at the intake gaskets, if they are leaking it will cause a vacuum leak and the engine and computer will try to compensate for the leak. when the engine heats up all the components expand and seal the leak. whn the engine cools the leak opens up again.

[Mr. Smith]

Obviously you didn't read my post as I said and I quote "Could be the temp sending unit for the computer" And don't play semantics as it is a sending unit period.

Now where did I say it was the guage? Yea I thought so. Sylvan has a place for you.

Originally Posted by dr olds

it is not the temp send unit you need it is the coolant temp sensor.

[tdyer]

Ok, here is an objective opinion of those last three posts: Mr. Smith did say "for the computer", but he also said "sending unit", which a parts store would "probably" take as the one for the guage. It appears that Mr. Smith and dr olds both meant the same thing which is referred to as the "Coolant Temperature Sensor". I've recently replaced both the CTS and the Sending unit on two different Chevys. If you're going to replace the CTS, it is normally located near the thermostat. The one that talks to the guage only is usually located near a cylinder on the block. You won't need to bother with that one. The CTS is usually about $8 - $12 and only takes a few minutes to replace. Just drain enough coolant to drop below the thermostat and unscrew it. Put some teflon tape or RTV on the threads of the new one, before putting it in. Good luck. Your problem probably isn't that simple though.

[dr olds]

mr smith, obviously you were wrong in the "term" you stated . so if oregon712 who posted the problem would have walked into a parts store and asked for a temp send unit which is different then a coolant temp sensor he would have gotten the wrong part as tdyer explained. you obviously made a mistake, no problem but to insult someone over it, thats completely childish and immature. you made the mistake, grin and bear it. i am a ASE master tech, with 22 years hands on experience and i have worked for a chevy dealerworking on these vehicles everyday. so before you insult someone, get your facts straight first before you either give someone the wrong info or "try" to insult someones intelligence. have a nice day.

[horse482]

Well being a parts guy you don't know how many people come in asking for a sender instead of the sensor, if you go some where that has inteligent parts people then you should not worry about it, especially if they say it's for the computer.

[dr olds]

you are absolutely right, when i was in parts i could not tell you how many people came in asking for the sender instead of the sensor, when they would open the box and look at the part you would hear "thats not it" then you would go get the sensor. it got to the point that you would ask them up front is it for the computer or guage.

[roadrunner_70]

It would appear that Mr. Smith has a chip on his shoulder. It's difficult to learn from other's in an open forum when someone insults other's intelligence. Perhaps Mr. Smith, you should look to greener pastures for your information. The "Chevy talk" forum would be more to your liking!

[oregon712]

Hey everyone, Thanks for your input. The Truck was taken to several automotive shops, and still they can't seem to figure it out. I had them check the CTS and it checked out fine.(but is there really any way to check it, without pulling it out?) And something(sorry, i forget what it is called) that normally puts out 5.0volts, was only putting out 2.7 volts, was replaced. And the fuel pump was just replaced too(but the problem existed before fuel pump went bad). Could it be the injectors, but if it was the injectors, wouldn't it still make the truck idle funny all the time, not when it was just cold? I may just have the CTS replaced anyway. If you guys have anymore ideas please feel free to tell me, i'd really appreciate it. Thanks!