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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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Location: Oregon
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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