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Crazy high idle. HELP!!

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Old 09-19-2017, 04:24 PM   #1  
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Crazy high idle. HELP!!

WARNING!!! lots of info below. Sorry in advance.

I am (still) working on my 89 Camaro named Hellion. Last year I did 2.8 to 3.1 long block swap. This summer I (mostly)completed a '302 to '7730 swap. I also swapped out the 2.8L upper plenum and fuel rail with the 3.1L parts. The lower Plenum and intake are still 2.8L.
Before the intake swap I had a high idle issue that I thought was either the IAC or TPS sending a different signal than the new computer wanted. After the swap, same issue. I replaced the IAC( and set it to idle roughly at 900 with the throttle plate screw) and re-calibrated the TPS to .57 volts with the throttle plate closed.
Now at start up it revs to 2500-2800 then falls to about 1000-1500. After you start driving and closed loop takes over the IAC stops moving and the car starts idling at roughly 2000-2500.
Any thoughts on what could be the issue?

Also if anyone has any information regarding how to make the 2.8L VSS work with the '7730 I would greatly appreciate it.

Last edited by broke91firebird; 09-19-2017 at 04:27 PM. Reason: spelling :(
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Old 09-19-2017, 04:28 PM   #2  
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Re: Crazy high idle. HELP!!

Current Mods:
EGR delete and disabled in chip
Canister Delete and disabled in chip
AIR pump delete and disabled
1.6 roller tip rockers
16 degrees timing
headers
cat delete
2.8L CAI intake
3.1L serp. belt accessory set up
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Old 09-25-2017, 08:10 PM   #3  
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Re: Crazy high idle. HELP!!

Update! Vacuum gauge reads a rock solid 19-20 inches both at the fpr port and at the HVAC controls port at the back of the intake.
Anyone have any other ideas?
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Old 06-10-2018, 09:49 PM   #4  
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Re: Crazy high idle. HELP!!

More updates. I installed a 3.1l lover intake as the cold start injector was broken and causing a vacuum leak. I also replaced all the gaskets above. I've replaced the IAC and the TPS. I tried a new ECM this weekend and ran through the idle relearn found here: https://www.thirdgen.org/forums/v6/235452-idle-adjustment-procedures.html

I let the car sit 2 hours it started fine and idled at about 900 rpm. I fired it up this morning and its back to 2500 rpm idle.
anyone have any other ideas to check?
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Old 06-11-2018, 02:06 PM   #5  
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Re: Crazy high idle. HELP!!

the big vacuum line that runs from the lower intake to the IAC might have slipped off.
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Old 06-11-2018, 02:44 PM   #6  
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Re: Crazy high idle. HELP!!

Quote:
Originally Posted by WhiskeySierra6 View Post
the big vacuum line that runs from the lower intake to the IAC might have slipped off.
the car has been switched over to a 3.1 intake. The only vacuum lines left go to the MAP sensor, the fuel pressure regulator and the brake booster. All the other lines have been capped.
I figured it was a vacuum leak but all the hoses are new and all the gaskets from the intake against the heads on up are new
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Old 06-11-2018, 02:53 PM   #7  
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Re: Crazy high idle. HELP!!

Can an exhaust leak between the headers and heads cause a rich running condition and high idle?
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Old 06-12-2018, 11:42 AM   #8  
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Re: Crazy high idle. HELP!!

i had a high idle that nothing seemed to solve. new IAC , new tps, checked all vacuum lines. eventually I had megasquirt installed on the car and it hasn't been back.
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Old 06-12-2018, 11:46 AM   #9  
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Re: Crazy high idle. HELP!!

Quote:
Originally Posted by broke91firebird View Post
Can an exhaust leak between the headers and heads cause a rich running condition and high idle?


it could mess with your 02 readings and thus your A/F ratio. not sure how it would affect idle.
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Old 06-13-2018, 09:44 PM   #10  
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Re: Crazy high idle. HELP!!

Try exposing the throttle body and with the engine idling, put your finger over the IAC inlet. It should stall quickly. If it doesn't there's a vacuum leak or the throttle is adjusted too far open. Try to do this while it's having the fast idle issue, just in case it's an intermittent leak.
The throttle adjustment screw should just be used to keep the throttle from sticking in the bore. It shouldn't be used to adjust the idle speed. You might have it open too far, but I don't think that explains your problem since it isn't consistent.

Make sure you aren't getting any check engine codes while the issue is occurring (and make sure the light works). I've had a syndrome like this before on a Fiero but I got a code from it. What happened was my IAC electrical connector was broken, and after messing with it, I had the pins plugged incorrectly.

If you're not getting an error code, and you've confirmed that the air is going through the IAC and not a leak, then it implies the ECM is intentionally opening the IAC to run that fast idle. Otherwise you should get a code complaining that it can't control the idle.

The most likely reasons I can think of that it would intentionally run such a fast idle is if there's an issue with the coolant temperature sensor, or something isn't quite right about the ECM install or configuration. Is this a stock chip, or one you programmed?

There might also be other scenarios where it would run a faster idle, like if it thinks the battery voltage is low or maybe if it thinks the engine is overheating, but I don't think it would ever speed it up that much.
If you have the means, try looking at all the sensor data on a laptop as it's idling and see if anything looks wrong.
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Old 06-13-2018, 10:36 PM   #11  
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Re: Crazy high idle. HELP!!

The only thing I saw weird the last time I dataloggged is when idling too fast the IAC will stick at a certain point. Say 70 steps. It will climb from this point but always drop back down to it. The only code I had last time was vss low(its not hooked up).
ill check the other things you mentioned this weekend when I go to where the car's stored. Thank you
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Old 06-14-2018, 07:59 AM   #12  
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Re: Crazy high idle. HELP!!

are you running the stock injectors?
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Old 06-26-2018, 06:09 PM   #13  
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Re: Crazy high idle. HELP!!

No it has 16lb aftermarket injectors. The chip I made accounts for that. I noticed yesterday that while at about 2000rpm the MAP sensor is reading in the 70-80 range. It makes out at 97.17 with the key on engine off. It also won't read anything but 97.17 unless the car is running. I tried to pull a vacuum on it with the key on engine off.
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Old 08-10-2018, 03:15 AM   #14  
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Re: Crazy high idle. HELP!!

So I believe I've narrowed the issue down. I pulled all 6 plugs yesterday and 5 plugs were a whitish grey. The #1 plug was wet with gas. So that explains why its seeing rich while running lean. This morning I removed the injector rail and left the injector in question pointed into a cup for an hour with nothing leaking out.
could just this cylinder be getting poor spark or (hopefully not) could this be a compression thing? Or do I simply have an injector tat flows more than it should? Last time I checked all injectors had about 16 ohms resistance
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