Hunting Idle @ Startup - My Solution
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From: RVA
Car: 89RS,89TBI FB, 91Z28, 89TPI FORMULA
Engine: 357 SBC TPI
Transmission: World Class T-5 (for now)
Axle/Gears: Strange 12-bolt 3.73
Hunting Idle @ Startup - My Solution
89 Formula TPI 357
I had an issue only when I started the car cold; the idle would hunt & bounce, gradually at first then within 10 seconds, it would bounce from 500 to 1200 RPM then choke itself off. I had to give it gas for about 10-15 seconds until the issue resolved itself. This was unacceptable considering it is a weekend car. I had to do mondo research, reading dozens of posts not particularly pertaining to my specific issue to gather up the info and "tests" to perform to diagnose the problem. This post is a summary of my
, and how I fixed it.
What I Tried:
-tighten header bolts
-check for vac leaks
-visual the MAF, make sure nothing's broken (mine is descreened)
-check for correct fuel pressure (I run 48 psi)
-verify O2 is working properly (with scanner)
-check TPS (.54)
-check timing (6*)
-verify IAC is working
{remove IAC from TB, plug IAC back into harness, jumper ALDL A/B, KOEO, watch IAC to verify pintle moves in & out; if it does not move, it's dead}
-IAC Test #2, if it is working (with TB & IAC bolted back on the car), jumper ALDL A/B, wait 30 seconds, unplug IAC harness, un-jumper ALDL, start the car cold; if the problem goes away or is diminished, the IAC isn't working properly or is part of multiple problems. Clean or replace the IAC
My Results:
1) The IAC was dead (didn't hum, didn't move at all)
2) Timing somehow jumped to 10* base
3) TPS couldn't hold a steady voltage; I could tap it with my finger and the voltage would vary greatly; give it gas and the voltage would hang and not return to the idle value
The Fix:
I replaced the IAC & TPS (WITH DELCO PARTS, both were Advance Auto pieces that lasted 5 years working only on weekends. Pay the extra money and save yourself the headache!). I also reset the base timing to 6*. Problem solved, it starts and runs like new.
Hopefully this will help and save someone from pulling their hair out and having to endure that one smartass who tells you to.
Eric
I had an issue only when I started the car cold; the idle would hunt & bounce, gradually at first then within 10 seconds, it would bounce from 500 to 1200 RPM then choke itself off. I had to give it gas for about 10-15 seconds until the issue resolved itself. This was unacceptable considering it is a weekend car. I had to do mondo research, reading dozens of posts not particularly pertaining to my specific issue to gather up the info and "tests" to perform to diagnose the problem. This post is a summary of my
, and how I fixed it.What I Tried:
-tighten header bolts
-check for vac leaks
-visual the MAF, make sure nothing's broken (mine is descreened)
-check for correct fuel pressure (I run 48 psi)
-verify O2 is working properly (with scanner)
-check TPS (.54)
-check timing (6*)
-verify IAC is working
{remove IAC from TB, plug IAC back into harness, jumper ALDL A/B, KOEO, watch IAC to verify pintle moves in & out; if it does not move, it's dead}
-IAC Test #2, if it is working (with TB & IAC bolted back on the car), jumper ALDL A/B, wait 30 seconds, unplug IAC harness, un-jumper ALDL, start the car cold; if the problem goes away or is diminished, the IAC isn't working properly or is part of multiple problems. Clean or replace the IAC
My Results:
1) The IAC was dead (didn't hum, didn't move at all)
2) Timing somehow jumped to 10* base
3) TPS couldn't hold a steady voltage; I could tap it with my finger and the voltage would vary greatly; give it gas and the voltage would hang and not return to the idle value
The Fix:
I replaced the IAC & TPS (WITH DELCO PARTS, both were Advance Auto pieces that lasted 5 years working only on weekends. Pay the extra money and save yourself the headache!). I also reset the base timing to 6*. Problem solved, it starts and runs like new.
Hopefully this will help and save someone from pulling their hair out and having to endure that one smartass who tells you to
.Eric
Last edited by BOSS 357; Nov 21, 2010 at 09:54 AM.
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