So my father has a shop and he has recently received an 1986 Chevrolet S10 2.5 TBI with a perpetual very high idle(No tach, I assume it is 2200-2500rpms) from a friend of a friend that he is just trying to help out.
The owner says the car's idle slowly got higher and higher as he drove it over time. He replaced the IACV, no change. My dad wasn't told the IACV was changed. He replaced it again still no change, replaced the CTS, no change, replaced the computer, no change. So he called me and I went over to help.
He told me what he did. I tested all the connectors, sensors and wires to the computer, no opens, and no excessive resistance and they all tested good. I put everything back together except IAC and plugged the hole and it idles great. There are no vacuum leaks. I tested the IAC, no opens and no excessive resistance. So I jumped the A and B on the ALDL, to put it in diagnostic mode and push the pintle out, it did nothing.
I told my dad it was bad he got another one and replaced it after we tested it, it worked. On first start up in the garage it started at a little high of rpms(around 1500) but settled down to a normal idle and ran good. Took it for a test drive and it ran good. Parked it outside and went inside to clean up and BS for a little bit. Went back outside started it up and it was high rpms again(2200-2500rpms). Around 30 seconds to a minute it dropped down to about 1500rpms. After another 30 seconds to a minute it dropped down to a normal idle.
It does this every time exactly the same no matter how soon I start it back up. I can start it up and after a minute or two the idle drops to normal. Shut it off and immediately start it back up and it goes through the same process, of between a minute or two to drop back into normal idle.
I wrote out this much so you have an idea of what has been done and how the vehicle is operating. Has anyone ran into this before? I have been trying to figure it out since I got home and have been searching the internet.
I found a Fiero forum that has the same 2.5 TBI engine and someone posted a copy of a TSB that stated that this is normal operation in cold weather. That when the computer receives info that it is cold it does this controlled vacuum leak through the IAC to raise the rpms so the vehicle doesn't stall out. And that it steps down the idle to a slightly lower rpms to still insure it doesn't stall before dropping to normal idle. And that this process takes between 1-2 minutes for this process in the cold.
I am basically asking if someone has experiences with these and can confirm whether this is normal operation. The TSB on the forum is not an actual copy, it is pieces of one that they said was from a TSB. And I don't feel confident trusting the source 100%. Sorry for the long post.
The owner says the car's idle slowly got higher and higher as he drove it over time. He replaced the IACV, no change. My dad wasn't told the IACV was changed. He replaced it again still no change, replaced the CTS, no change, replaced the computer, no change. So he called me and I went over to help.
He told me what he did. I tested all the connectors, sensors and wires to the computer, no opens, and no excessive resistance and they all tested good. I put everything back together except IAC and plugged the hole and it idles great. There are no vacuum leaks. I tested the IAC, no opens and no excessive resistance. So I jumped the A and B on the ALDL, to put it in diagnostic mode and push the pintle out, it did nothing.
I told my dad it was bad he got another one and replaced it after we tested it, it worked. On first start up in the garage it started at a little high of rpms(around 1500) but settled down to a normal idle and ran good. Took it for a test drive and it ran good. Parked it outside and went inside to clean up and BS for a little bit. Went back outside started it up and it was high rpms again(2200-2500rpms). Around 30 seconds to a minute it dropped down to about 1500rpms. After another 30 seconds to a minute it dropped down to a normal idle.
It does this every time exactly the same no matter how soon I start it back up. I can start it up and after a minute or two the idle drops to normal. Shut it off and immediately start it back up and it goes through the same process, of between a minute or two to drop back into normal idle.
I wrote out this much so you have an idea of what has been done and how the vehicle is operating. Has anyone ran into this before? I have been trying to figure it out since I got home and have been searching the internet.
I found a Fiero forum that has the same 2.5 TBI engine and someone posted a copy of a TSB that stated that this is normal operation in cold weather. That when the computer receives info that it is cold it does this controlled vacuum leak through the IAC to raise the rpms so the vehicle doesn't stall out. And that it steps down the idle to a slightly lower rpms to still insure it doesn't stall before dropping to normal idle. And that this process takes between 1-2 minutes for this process in the cold.
I am basically asking if someone has experiences with these and can confirm whether this is normal operation. The TSB on the forum is not an actual copy, it is pieces of one that they said was from a TSB. And I don't feel confident trusting the source 100%. Sorry for the long post.
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