2.8 starts bogging with IAC connected? (Page 1/3)
Additivewalnut JAN 18, 11:19 PM
Got a weird one for y'all. 86 2.8 4spd, I have the IAC unplugged and manually adjusted to anywhere from a 900-1100 rpm idle by moving the IAC pintle in and out by hand. Now as you can imagine, this makes cold starts difficult. Problem is that if I have the IAC plugged in, then the car bogs HARD, just chugs and if I can get it to a higher RPM then it'll shoot a hell of a flame. If there's a solution to be had that's great, otherwise, I guess it works fine enough unplugged. My gut reaction says wiring or PCM, but I have no basis for that. What do you guys think?
1985 Fiero GT JAN 19, 01:27 AM
Is the flame out the exhaust, or is it a backfire (out the intake), symptoms of chugging real hard and backfiring if you give it gas, and generally acting like that can be TPS sensor, try proving it with a volt meter and seeing what it reads with the IAC unplugged, and then with it plugged in, potentially there's some sort of interference or short between the two sensors that causes the TPS to go out when it is connected, may not be the reason, but that is what first came to my mind.

[This message has been edited by 1985 Fiero GT (edited 01-19-2024).]

82-T/A [At Work] JAN 19, 07:45 AM

quote
Originally posted by Additivewalnut:

Got a weird one for y'all. 86 2.8 4spd, I have the IAC unplugged and manually adjusted to anywhere from a 900-1100 rpm idle by moving the IAC pintle in and out by hand. Now as you can imagine, this makes cold starts difficult. Problem is that if I have the IAC plugged in, then the car bogs HARD, just chugs and if I can get it to a higher RPM then it'll shoot a hell of a flame. If there's a solution to be had that's great, otherwise, I guess it works fine enough unplugged. My gut reaction says wiring or PCM, but I have no basis for that. What do you guys think?




Is your computer giving you any error codes?
Additivewalnut JAN 19, 10:28 AM

quote
Originally posted by 82-T/A [At Work]:
Is your computer giving you any error codes?



Nope, code free. Granted I got this car with an MSD box installed and the EGR deleted so its not out of the question that the previous guy could've gotten the pcm tuned poorly
Additivewalnut JAN 19, 10:30 AM

quote
Originally posted by 1985 Fiero GT:

Is the flame out the exhaust, or is it a backfire (out the intake), symptoms of chugging real hard and backfiring if you give it gas, and generally acting like that can be TPS sensor, try proving it with a volt meter and seeing what it reads with the IAC unplugged, and then with it plugged in, potentially there's some sort of interference or short between the two sensors that causes the TPS to go out when it is connected, may not be the reason, but that is what first came to my mind.




I'll look at that tonight. It's definitely out the tailpipe. Makes a neat party trick LOL
82-T/A [At Work] JAN 19, 11:36 AM

quote
Originally posted by Additivewalnut:

Nope, code free. Granted I got this car with an MSD box installed and the EGR deleted so its not out of the question that the previous guy could've gotten the pcm tuned poorly




Interesting... does the Service Engine light even come on when you start the car? I'm wondering if the ECM is actually totally dead.
1985 Fiero GT JAN 19, 11:43 AM
Just out of curiosity, probably a shot in the dark, but is the aldl connector bridged, because I know that when it is put in diagnostic mode, and started, the IAC is moved all the way closed, which might make it "chug" and it effects the timing, which might potentially make it shoot flame at higher rpms?
Additivewalnut JAN 19, 12:00 PM

quote
Originally posted by 82-T/A [At Work]:
Interesting... does the Service Engine light even come on when you start the car? I'm wondering if the ECM is actually totally dead.



It does, and it'll flash the test code when the aldl is jumpered.
Additivewalnut JAN 19, 12:02 PM

quote
Originally posted by 1985 Fiero GT:

Just out of curiosity, probably a shot in the dark, but is the aldl connector bridged, because I know that when it is put in diagnostic mode, and started, the IAC is moved all the way closed, which might make it "chug" and it effects the timing, which might potentially make it shoot flame at higher rpms?



No, but I did check that. I jumped it to reset the iac so I also know that the wiring there is sound
1985 Fiero GT JAN 19, 04:26 PM

quote
Originally posted by Additivewalnut:


No, but I did check that. I jumped it to reset the iac so I also know that the wiring there is sound



Ok, I have no idea what it may be then