DerekTheGreat
Forum Regular
Hey all,
Thought I'd share this with you guys since I don't think I've seen anyone mention this before, I've heard about the throttle shaft & gaskets being blown out but not this.. Also more fuel for the fire that says, "Diagnose, not replace."
Anyway, I've had an erratic idle problem with our '89 K1500 5 speed since it had the bad motor in it. New used motor went in and the problem still existed but wasn't as frequent. Truck would want to idle @600-650 RPM when warmed up but often while just sitting there already idling at 600-650 it would start to idle up to almost 1,500 rpm at times. I often noticed this coming off the freeway, I figured it had detected a "stall condition" and I read somewhere that stall condition to do with throttle position + low MAP values, which causes the truck to idle higher for about 10 minutes if the condition is no longer present. I'd get some aggravated with it at times I'd flip the key off and back on, which would usually cause it to want to idle normal again so I did figure that's what it was. I looked into the EGR, cleaned that all out, swapped MAP sensors & checked I had no leaks by using a vacuum pump on the MAP tube. Still did it. Then I busted out my MT2500 scanner brick. I did this before but never sat and watched it. Sure enough, some 10-15 minutes of watching the thing, just as I was about to wrap it all back up and presto. I saw IAC counts go from 6-20ish, the computer was indeed commanding a higher idle. Then I saw why, my TPS voltage went from 0.58-0.68 and then up to 0.75, all on it's own. It kept jumping around and as it did that, so would the idle. As Eric O would say, "There's your problem, lady!" I haven't swapped it out yet as I've got the earlier style TPS that is hard to find but I'm confident that is the problem. So, for anyone with a similar problem, try looking there first or as well.
Thought I'd share this with you guys since I don't think I've seen anyone mention this before, I've heard about the throttle shaft & gaskets being blown out but not this.. Also more fuel for the fire that says, "Diagnose, not replace."
Anyway, I've had an erratic idle problem with our '89 K1500 5 speed since it had the bad motor in it. New used motor went in and the problem still existed but wasn't as frequent. Truck would want to idle @600-650 RPM when warmed up but often while just sitting there already idling at 600-650 it would start to idle up to almost 1,500 rpm at times. I often noticed this coming off the freeway, I figured it had detected a "stall condition" and I read somewhere that stall condition to do with throttle position + low MAP values, which causes the truck to idle higher for about 10 minutes if the condition is no longer present. I'd get some aggravated with it at times I'd flip the key off and back on, which would usually cause it to want to idle normal again so I did figure that's what it was. I looked into the EGR, cleaned that all out, swapped MAP sensors & checked I had no leaks by using a vacuum pump on the MAP tube. Still did it. Then I busted out my MT2500 scanner brick. I did this before but never sat and watched it. Sure enough, some 10-15 minutes of watching the thing, just as I was about to wrap it all back up and presto. I saw IAC counts go from 6-20ish, the computer was indeed commanding a higher idle. Then I saw why, my TPS voltage went from 0.58-0.68 and then up to 0.75, all on it's own. It kept jumping around and as it did that, so would the idle. As Eric O would say, "There's your problem, lady!" I haven't swapped it out yet as I've got the earlier style TPS that is hard to find but I'm confident that is the problem. So, for anyone with a similar problem, try looking there first or as well.
