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Strange Idle

 
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Old 11-18-2011, 12:24 AM
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Strange Idle

Hey guys. I looked all over for this problem but cant seem to find a thread on it. I have a 1990 Si with the B21a1 and its displaying strange idle chatacteristics. While sitting still yhe idle is normal. But whenever its moving more than 3 mph in any direction it will idle anywhere from 2300-3100 whenever the clutch is in or in neutral. Upon coming to a stop, it'll hang there for about 3 or 4 seconds, then drop back down to 850. It has a new TPS, the FITV is clean and re-adjusted and the IAC is clean. The odd thing is if you disconnect the TPS when the engine is warmed up, it wont do it. Like i said, Ive put a new TPS in it and then one that i picked up in a yard. Same issue. Any insight would be awesome as I imagine i look like a tool coming up to a light, stop sign, or gas pump with my engine screaming at 3k, hahah.
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Old 11-18-2011, 04:55 AM
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Re: Strange Idle

There's a lot involved here. Check all vacuum lines to see if they're tight and condition. Re-tighten intake manifold gasket. Sometimes a clean idle control valve doesn't mean it's good one. See if anything is biding on the throttle cable and check throttle return spring. Are there any codes flashing? Sometimes you can get codes without the check engine light working. Also you could borrow a loaner ecm computer for that b21 engine to see if it's the throttle position sensor or the computer. gOOD LUCK.
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Old 11-18-2011, 04:59 AM
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Re: Strange Idle

fORGOT TO ASK....iF IT'S WARMED UP AT IDLE, And you rev it, Does the idle stick at 3000 rpm's? If it does then it might be the return spring for the throttle body or somethings wrong with the cable. Wish I could see it while it was revved up to see how fast the throttle valve closes.
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Old 11-18-2011, 08:48 AM
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Re: Strange Idle

When its moving it will stick. Stopped it wont. Its strange, never seen a speed dependant idle issue brfore. I know of the fluctuating idle and the constant high idle, but this is news to me. Ill try to.throw up a vid later today showing off the problem. You could probably take more from that than me. Haha
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Old 11-18-2011, 09:21 AM
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Re: Strange Idle

Anything really above 1500 rpm sounds like something to do with the throttle manually being open too much or an extremely bad vacuum leak. Tighten down the two nuts holding the EGR valve too.
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Old 11-18-2011, 09:49 AM
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Re: Strange Idle

I'm having a similar problem, but I have a 5th gen
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Old 11-18-2011, 10:12 AM
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Re: Strange Idle

Did a little research on the Preludezone and found that only three things will cause it. Too tight of a cable at the throttle body.Bad fast idle valve and a bad idle control valve. Now remember, 25 years went by and my idle control valve went out. Cleaning it didn't do squat. So just cause something is clean doesn't mean it's working like it did from the factory. Gotta keep us posted though. You never know.... It might happen to me and I'd want to know what the fix is. Sounds really like one of those two valves cause it still idles good. Too tight of a cable might not let you idle normal rpm's.
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Old 11-18-2011, 08:03 PM
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Re: Strange Idle

I had a friend with a problem like this, he said was the map sensor or something like that, I would look for it and see what comes out

Last edited by XLude23; 11-18-2011 at 08:21 PM.
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Old 11-18-2011, 09:07 PM
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Re: Strange Idle

haven't found a good answer yet but should check for leaks on all the vacum hoses specially on the one going to the M.A.P. sensor, also check for codes related to the T.P.S.
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Old 11-18-2011, 10:43 PM
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Re: Strange Idle

I went to the yard to grab an IAC. When i brought it back i saw that it was different between tje 2.0 and 2.1. Sooo still running my old IAC. Ill have a gander at my MAP as soon as I can, but with a 12 hour shift tomorrow, it looks as if Ill have to wait until Monday. Thanks for the tips everybody!
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Old 11-19-2011, 02:25 AM
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Re: Strange Idle

This kids temper was once idle...

Until suddenly the o2 sensors went bad!!!!!

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