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Old 06-12-2009, 10:58 AM   #1
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Default Idle speed way too high

I had a problem where the idle speed keeps getting higher until it's unbearably high (2k rpm +).

Turning the idle speed adjustment screw made this ok for a while, but with it turned all the way down the idle kept getting higher. This happened over a period of weeks.

I cured this problem by replacing the throttle body with a 2nd hand part. This lasted for a good 6 months or so then the exact same problem happened again. I've just replaced the throttle body again and i'm back to a 900rpm idle as set in my MSPNP. I'm not sure if this will fix the problem for good or if it's just a matter of time before this happens again.

What is going on? Has anyone got any ideas why this is happening?


Car Details:

1994 Eunos Roadster NA8C
MSPNP
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Old 06-12-2009, 11:05 AM   #2
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check for vacuum leaks first off. use brake cleaner and spray it all around the flanges of the TB.
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Old 06-12-2009, 11:09 AM   #3
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Well the problem is now resolved, but I'm not sure how long it will last. If it was a vacum leak I'd expect the problem to still be there even after I replaced the TB? Unless the nuts holding the TB on have come loose over time?
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Old 06-12-2009, 11:17 AM   #4
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ah, i read it wrong. i didn't see you replaced it again.

its possible the shaft seal went bad. I had the same issue once where i just couldnt get my TB to seal between the IAC and TB....I ended up just swapping it out
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Old 06-12-2009, 11:21 AM   #5
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Some more info:

Ok I'm running a MSPNP and I idle around 13.3:1 I'll check the vac pressure at idle, but replacing the TB has fixed this twice so I'd be inclined to think its a problem with the TB and not a vacuum leak elsewhere. Surely if it was a vac leak the problem would still exist even after I replaced the TB. I also don't run a MAF.

The idle raised over a course or weeks / months. At its worst the idle was around 1800 when i first switched the engine on, and upto 2200rpm after a drive.

There was also a deep sucking noise present which has now disapeared after replacing the TB. It's a different noise from the noise it would make with me holding the throttle at 2k.

So you think its the gasket between the TB and the idle speed control valve?
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Old 06-12-2009, 11:22 AM   #6
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I replaced my TB and caused a vacuum leak. Some of the TB to IM gasket broke off allowing air to leak in. You might want to check there. Of course do a check like Brain suggested to narrow down the problem.
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Old 06-12-2009, 11:25 AM   #7
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The metal gasket betwen the TB and Intake Manifold is all in one piece and like I explained, it's now idling perfectly after replacing the TB. The reason I started the thread is because this has happened twice now.
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