Rough Idle and rough shift

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LLkoolskillet

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First post here, quick run down on the truck. Its a 1992 Chevy K2500 7.4L Scottdale Ext Cab LB, just turned over 100k :D From my research I believe the truck should be idling around 600rpm, please correct me if I am wrong. Instead it idles between 950-1100. The idle will raise and lower when its cold in park and will raise and lower just letting it idle in drive moving about 20mph or less. Oh and it will drive itself up to 20 mph. Again my research leads me to the IAC. Does this sound correct?

Now my second issue is, when I fire it up the service engine light will come on. When its on the truck will not shift into 2nd unless I jam on it hard. Then it will shift and man does she shift HARD. So I cruise around the block in 1st to get a little heat built up. Pull over and turn her off, pull the key out and let everything reset for about 30 sec. Then I fire it back up and immediately put it in gear. light doesnt come on. Once in gear it runs like its going to choke. Now all these symptoms go away once shes all warmed up. I can go where ever all day long and not have a single issue. I only experience these during the initial start up. Any help is greatly appreciated.
 

Annihilator

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Possibly a vacuum leak. My 305 TBI had the same symptoms. Ended up being a hole in a rubber hose coming off intake.
 

LLkoolskillet

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Ill go out and do some searching. Hopefully its something simple. The truck has sat for the better part of 5 yrs.
 

Brandon_Lutz

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For the fast idle, get some carb cleaner and spray around all of your vacuum lines with the truck idling. If there is a vacuum line leak, you will know immediately when you find it. I had a similar situation with my 95 GMC 2500. It kept idling really fast. It turned out that the PCV valve was the culprit. I replaced it and the idle went to a much smoother and lower idle after doing so.
 
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