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L98 is ugh!

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Old Jan 1, 2009 | 05:01 PM
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Default L98 is ugh!
my dad just did a head gasket on his 91 L98. he had everything back together but it idled very high. (like 1200 rpm) so he messed with it and took it apart again. when he put it together the idle was all screwed up. no the idle is so low it won't stay running unless you rev it. when you rev it, it runs and sounds perfect. but as soon as the rpm goes down, it sh*ts the bed on him. anyone have any idea what this could be. he was saying something about he had to disconnect the vacuum hose from the pcv to make it run or something, but i'm not sure.
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Old Jan 1, 2009 | 06:01 PM
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Recheck the TPS setting.
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Old Jan 1, 2009 | 06:14 PM
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Its a vacuum problem somewhere. Recheck all the runner gaskets and any vacuum lines. Its common to forget about all the little black vacuum lines that go underneath the plenum.
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Old Jan 1, 2009 | 06:18 PM
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Originally Posted by Demonic85
Its a vacuum problem somewhere. Recheck all the runner gaskets and any vacuum lines. Its common to forget about all the little black vacuum lines that go underneath the plenum.
Or the brake line that attaches to the back of the plenum!
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Old Jan 1, 2009 | 08:56 PM
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Originally Posted by formul89
Recheck the TPS setting.
Non-adjustable TPS on the '91.
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Old Jan 1, 2009 | 09:51 PM
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Check for vacum leaks. Also try disconnecting the MAF and see if it runs any better.
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Old Jan 1, 2009 | 09:52 PM
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Originally Posted by Demonic85
Its a vacuum problem somewhere.
It's probably a vacuum problem.

I'd also suggest checking the ignition timing too. When I replaced the head gaskets on my '89, it idled like crap until I set the ignition timing.

Good luck!
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Old Jan 1, 2009 | 09:52 PM
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Originally Posted by Radioshop
Check for vacum leaks. Also try disconnecting the MAF and see if it runs any better.
No MAF sensor on '91. They used a MAP sensor instead.
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Old Jan 1, 2009 | 10:34 PM
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How about the Idle Air Control (IAC) Valve? Did you check that?
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Old Jan 1, 2009 | 11:01 PM
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Don't forget to unplug the EST when you check / set the timing.
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Old Jan 2, 2009 | 01:46 AM
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Originally Posted by janarvae
Non-adjustable TPS on the '91.
Forgot about that.
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Old Jan 2, 2009 | 10:54 AM
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MY91vette -Hey - where did he go? Did you get it to settle down?
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Old Jan 2, 2009 | 10:59 AM
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no not yet. its a tad cold here and theres a foot of snow on the ground.
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