My Fiero GT 1985 manual trans., developed a problem or high idle, near three thousand RPM, I have checked the engine and can find no Vacumn leaks, I have replaced the throdle position sensor.....any help would be appreciated..thanks
Idle high Problems
- Thread starter rockygt
- Start date
The IAC can be bad. It is mounted on the side of the throttle body with 4 wires sticking out of it.
The EGR tube could be cracked or some other vacuum leak.
An easy check to perform is to remove the intake tube from the throttle body. Start engine. Just inside the TB you will see a large port on the bottom. Put your finger over it and block it.
If the engine dies the IAC is bad or or very dirty and stuck open. If the engine keeps running you have a vacuum leak somewhere.
The EGR tube could be cracked or some other vacuum leak.
An easy check to perform is to remove the intake tube from the throttle body. Start engine. Just inside the TB you will see a large port on the bottom. Put your finger over it and block it.
If the engine dies the IAC is bad or or very dirty and stuck open. If the engine keeps running you have a vacuum leak somewhere.
javojjaaf
New member
im having this problem now with my 88. it was fine until i pulled all the fuses to check them and messed with the connection to the temp sensor...the plug on the wires that go to it is broken. i dont think this would cause it to idle up, but did i miss a fuse that powers the sensors? i replaced the IAC today because when i covered the opening in the throttle body like you said it died, well same thing with the new one.....? what ya think?
One thing that should be noted is that once you replace the IAC, The vehicle has to be driven up to 40mph. This is the speed at which the computer resets the IAC for proper idle level.
As for broken wire to temp sensor, Which temp sensor? the one on the head, The one for the fan, or the one for the computer? The one for the computer could cause issues. The other 2 will not affect the engine running.
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javojjaaf
New member
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javojjaaf
New member
its the temp sensor on the head, so no worries then? will the computer still know when to turn on the fan if its not plugged in? also, when i said i messed with the fuses checking them....are there any that will cut power to the sensors like the IAC?
P.S. - i just drove the car a couple of miles like you said to set the iac, but when i got back it was still idling around 2 grand. so i pulled the intake hose again and covered the iac opening in the throttle body and i get the same thing...the engine dies. i can control the idle if i allow some air to pass, but its like the sensor isn't getting the right signal or something. im stumped
thanks
P.S. - i just drove the car a couple of miles like you said to set the iac, but when i got back it was still idling around 2 grand. so i pulled the intake hose again and covered the iac opening in the throttle body and i get the same thing...the engine dies. i can control the idle if i allow some air to pass, but its like the sensor isn't getting the right signal or something. im stumped
thanks
javojjaaf
New member
delete post...replied one to many times
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First go to this link http://www.fieronews.net/fusion/downloads.php
Under 1985 you will find the driveability and emisson manual for troubleshooting.
Under 1986 you will find a factory service manual with wiring diagrams. (1985 and 1986 fieros are identical with respect to the engine harness and computer)
If you have replaced the IAC and it appears to not work, You have either a bad wire, bad connector, or bad computer. The manuals above will show you what color wires do what and will give you a detailed flow chart on how to isolate where/what the problems is.
Under 1985 you will find the driveability and emisson manual for troubleshooting.
Under 1986 you will find a factory service manual with wiring diagrams. (1985 and 1986 fieros are identical with respect to the engine harness and computer)
If you have replaced the IAC and it appears to not work, You have either a bad wire, bad connector, or bad computer. The manuals above will show you what color wires do what and will give you a detailed flow chart on how to isolate where/what the problems is.
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javojjaaf
New member
Yes it is about the same, But if you have a 1988, Just download the 1988 service manual. The downloads are listed by years. Click on 1988.
The original person has a 1985.
Thank you for your reply... and I might add you you were correct in your assessment....in my case it was a cracked EGR TUBE....thank you for your help.....
Thanks for your correct response to my problem Orief. The EGR tube was cracked at the plenum, after seeing its construction this must be a common problem. Again many thanks for sending me in the right direction, with all of your checks.
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The Fiero store sells a copy of the 1988 version which has a more flexible tube which eliminates future cracking.
http://www.fierostore.com/Product/Detail.aspx?s=67019
javojjaaf
New member
im still having trouble with mine. it still idles around 2 grand and seems to be rich. i have replaced the IAC and the MAP sensor with no help. today i found a vacuum line broken that goes from the EGR solenoid to the firewall and continues to the bottom of the air filter box. i replace the hose and drove a few miles but it didnt make a difference. also, my egr valve looks like its in bad shape...but if i lift up on the underside of it the car will idle down, but runs rough. i also dont have a strong vacuum coming from the egr solenoid by pulling the line off the egr valve. could someone tell me if they get a strong pull from that hose on the egr valve please and any other ideas other than vacuum leaks that i may not have found? thanks