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Hello,


I'm not sure if this is in the right area or not, but I am having an issue with my 1990 Chevy C1500 305 5.0lL.


Originally I bought the truck to use as a work truck from Tyson Foods. The truck did have one major problem that I could see from the test drive: it would idle very rough and flat out die on the highway if you let your foot off of the gas pedal. I figured the problem was in the TBI. I removed the TBI from the truck, took it apart to try and rebuild it, and the spring inside the throttle body broke off into 3 pieces. Apparently, you also can't buy an aftermarket spring for this. So, I finally found a replacement at a junkyard. I put the new(old) throttle body on my truck and it seems to be working like a champ! My biggest problem now is that the truck is idling as if I placed a heavy block of lead on the gas pedal. I noticed that there was an air valve on the back of the TBI that had no vacuum line. I looked up the vacuum diagram and it turns out there is supposed to be a vacuum line going to the MAP sensor in this truck. Since there was no MAP sensor in my truck at all....I figured this would be the source of my idling problems. I just received a new MAP sensor from eBay today, but no dice. My truck is still idling entirely too high. Does anyone have any sort of experience with this?


Thanks

abalognedude

the IAC motor may be stuck or not responding

Allan In NE

You have a vacuum leak going on somewhere. Did you remember to replace the TBI gasket?


Allan

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Allan, you mean the one that sits directly below the TBI?


Yes.

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Ok so, I have replaced the IAC.....now it's idling even higher. I did notice that the vacuum line going from the TBI to the PCV valve is actually two separate lines. There is a boot and a smaller line that feeds into a much larger line(250 PSI). I'm not sure if this is normal or not. The PCV valve is also disgusting so it probably needs replacing anyway. Does anyone have any ideas after that?