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1990 Pontiac sunbird 2.0 runs rough, won't idle after warm(in park or drive)

(1990 Pontiac Sunbird)
in Seattle, WA on May 28, 2014
1990 pontiac sunbird 2.0 Naturally aspirated, 2 door convertible, carbureted, automatic, 206K.
(PROM, ECM work no check engine code). Runs and drives fine first 30 min highway and most days around town. After 30 min (good and warm) it runs quite rough and won't hold an idle (or anything below 1500RPM's really) whether in park neutral drive. in any gear I can keep my foot on the gas and it won't die, it doesn't run that bad while taking off when hot (not much sputter, loss of power) or while cruising (just an idle). I have basic tune up (cap, rotor, oil, plugs, wires, air filter) i ordered an IAC(idle air control valve, I think this may be it but….) I was going to do fuel filter also, that shouldn't fix it though. Fuel pump sounds good, haven't tested it yet but its in tank so heat shouldn't be the problem unless its vapor lock, or some type of heat/pressure problem?) any help or ideas would be much appreciated. If I figure it out I will post on here my solution.
Thank you
Displaying 1 answers & 5 comments
Popular Answer
on May 28, 2014
Your post says 'carbureted' , I think you figured out it's throttle body injection , since you're getting an IAC for it. IF that doesn't take care of the idle problem , reply with any new/different symptoms. I believe on the older GMs , you had to do an 'idle learn' procedure when putting on a new IAC. I think there's some tips on that in this site somewhere or maybe someone else with Better memory than me will post it here.
on May 28, 2014
yes, the throttle body is part of the carburetor? Thank you for the help.
on May 29, 2014
No...a throttle body is NOT part of a carburetor...... it has fuel injectors. A carburetor allows fuel to be DRAWN into the engine by the vacuum produced by the venturi....
on May 29, 2014
Ordered an IAC a few days ago from ebay ill post results when its here.
Any other help/tips/ideas/past experience would be much appreciated.
Thank you.
on May 29, 2014
post results from IAC I'll check back here.
on June 08, 2014
Put in IAC, seemed to "help" so far, (doesn't die after 2 test drives over 30min. still idles rough). also cleaned egr system after throwing (code 32 ?can't remember? "egr system fail" code) after installing IAC and driving.

Now the EGR is Getting vacuum on acceleration? not sure why yet but I think this is my last issue
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