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WEIRD ENGINE SYMPTOM,

 
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Old 01-25-2016, 09:35 PM
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WEIRD ENGINE SYMPTOM,

Hi guys. 1990 automatic.While going down the driveway in NEUTRAL the engine idles up to 2500 rpms till Istop then after a second or two it idles back to normal.Probably why the upshift cable I've been adjusting all week does no good. Anyone have this? I thought it was the iacv or fast idle valve? no codes. Help!
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Old 01-26-2016, 02:43 AM
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Re: WEIRD ENGINE SYMPTOM,

could be IACV, have you cleaned it out?

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Have you done a recent tuneup? how's your coolant level(radiator)?
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Old 01-26-2016, 03:40 AM
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Re: WEIRD ENGINE SYMPTOM,

I was thinking the iacv cause the only thing that idles it from high to low is that. Still don't know why it goes up when it rolls? When it starts in the morn, It idles at 770 instead of 1500. After a few minutes THEN it goes to 1500 till it's warmed up.Weird, Huh? My 91 manual starts at 1500 then after warming up goes to 770.
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Old 01-27-2016, 02:13 AM
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Re: WEIRD ENGINE SYMPTOM,

After researching the web most people say it's either the fast idle valve, iacv, or the throttle body. How would any of those components know I was riolling? Especially the fast idle valve. There's no wires going to that. I'm guessing the vss is telling the computer that I'm rolling and is affecting something else?
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Old 01-27-2016, 11:34 PM
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Re: WEIRD ENGINE SYMPTOM,

throttle body has throttle position sensor i think.
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Old 01-28-2016, 08:38 AM
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Re: WEIRD ENGINE SYMPTOM,

Some sites say that the throttle also is where the iacv sensor is. Also saw a video where a guy changed out his iacv cause of bouncy idle and the new one did the same. He later fixed it by replacing the iacv sensor and said it was at the throttle area. Will a manual trans throttle fit on an auto trans engine? Are they the same?
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Old 01-28-2016, 01:08 PM
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Re: WEIRD ENGINE SYMPTOM,

I'm not entirely sure about the 3rd gens, but I would imagine the TB for the auto would be a few mm smaller diameter intake than the manual. It's like that on some models. You must check out the idle thread, it's alot of reading, but it could answer more questions than we could, since it's so detailed.
I also am not sure of how the TPS is calibrated on the automatic and manual versions one might put a different value than the other at a certain throttle position. In which case you might have to change an ECU but I doubt it.
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Old 01-31-2016, 11:57 AM
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Re: WEIRD ENGINE SYMPTOM,

Problem fixed! Cleaned the iacv and same symptoms. Self acceleration. Next was either the ecm or throttle sensor. Luckily I saved my JDM intake and used the complete assembly with sensor. Just had to swap the bellcrank over cause mine's an auto. Works perfect now. Still don't know if the ecm is telling the iacv to spool up or not. While rolling in neutral, I'm sure the vss is telling the ecm something. After this fix, the Trans selector lockout works again. No more pushing down on a key just to get it out of Park.

Last edited by Lespaul59; 01-31-2016 at 04:14 PM.
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