'91 S-10 blazer idle problem
 

Hey everyone, I'm normally on the 67-72 side, but my dad has a problem with his s-10. When he does a cold start, it will idle to fast idle for a few seconds, then go to low idle like it should. But when it gets to low idle, it will idle down further like it wants to die, then goes back to low idle. It cycles like this until it is warm, then it idles like it should. We’ve tried replacing the MAP sensor, the O2 sensor, all plugs, wires, dist cap and rotor, all with no resolution. The next thing that he wants to try is to pull the gas tank, and replace the fuel pump, but it is getting fuel. Would a bad EGR valve do this? What about a bad catalytic converter? The truck has 200k miles, but runs like a champ when it does run. It’s the 4.3 TBI. Any ideas?

Re: '91 S-10 blazer idle problem
 

check the cts and there is another 1 i thionks its the iac. also the egr if not properly working can cause eradic running. pull it off and clean it, have a new gasket ready to go on and put a skim coat of anti seaze on the gasket so it can be removed for cleaning next time.

Re: '91 S-10 blazer idle problem
 

Thanks trailwart. I'll have him take a look at possibly replacing the egr. What is the cts though? Also, if the iac is what I think it is, isn't that the sensor in the air hat, close to the heat riser? I guess that is functioning properly. It does the same thing whether or not the air breather is on the tbi or not.

Re: '91 S-10 blazer idle problem
 

cts coolant temp senser. not sure if yours has 2, but they tell the computer the temps so it can adjust fuel. if its not working right it could send the signal to dump fuel and the 02 is telling it its rich so it can get lost and rpms will go up and down, up and dopwn

Re: '91 S-10 blazer idle problem
 

my '88 4.3 auto does something similar...when i first crank it (cold or warm), it idles up high for a few seconds...then it'll idle down to normal...i mean, i have to wait for it to idle down before i can put it into gear...i wasn't sure if this is normal either...my brother even asked me the other day if it was supposed to idle that high....but mine is fine after it idles down...the only other time is when you come to a stop in gear & under load, it vibrates really bad...but then it smooths out when you accelerate or even if in park/neutral