LT1-LT4 Modifications 1993-97 Gen II Small Block V8

LT1 Erratic Idle

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Old 09-07-2012, 11:09 AM
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Default LT1 Erratic Idle

Long time lurker here and current member over on Thirdgen, I'm a college student at Lewis University working on my Airframe & Power Plant Certificate and Business Degree, so I'm very hands on. Thanks in advance for all the help.

Scott


Background on the car:

1995 Z28 T-56. This is my first LT1, I bought the car with the top half of the motor sitting in the hatch and basically all the gaskets there up are new. No egr or air pump and they are properly blocked off.

The car runs great minus the fact that when it's been running a while (operating temp at least) the idle is horrible. The tach will basically jump wildly and the car feels like it wants to die but never does.

I've replaced plugs and wires already so I'm suspecting the ICM is going. The opti is supossed to be new and looks like it but I haven't been adventurous enough to take it apart. I just rebuilt my injectors (bosch ford blue tops all ohm at 15.4 and were flow matched) haven't found any vacuum leaks, ground are good and I'm stumped.
Old 09-07-2012, 11:18 AM
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Originally Posted by slomaro91
Long time lurker here and current member over on Thirdgen, I'm a college student at Lewis University working on my Airframe & Power Plant Certificate and Business Degree, so I'm very hands on. Thanks in advance for all the help.

Scott


Background on the car:

1995 Z28 T-56. This is my first LT1, I bought the car with the top half of the motor sitting in the hatch and basically all the gaskets there up are new. No egr or air pump and they are properly blocked off.

The car runs great minus the fact that when it's been running a while (operating temp at least) the idle is horrible. The tach will basically jump wildly and the car feels like it wants to die but never does.

I've replaced plugs and wires already so I'm suspecting the ICM is going. The opti is supossed to be new and looks like it but I haven't been adventurous enough to take it apart. I just rebuilt my injectors (bosch ford blue tops all ohm at 15.4 and were flow matched) haven't found any vacuum leaks, ground are good and I'm stumped.
does it happen as soon as it gets up to operation temp or is it random?

Does the car still pull in the upper rpms when your having the idle issues?
Old 09-07-2012, 11:30 AM
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it still drives just fine at anything above idle. No misses or anything and pulls smooth. The tach flickers like there's an ignition problem though.
Old 09-07-2012, 03:14 PM
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Sounds like your IAC may be the problem.
Old 09-09-2012, 06:55 PM
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So far I found one melted plug wire and my coil was not spaced off of te cylinder head. The idle doesn't hunt, the tach flickers. Which pointed towards an ignition problem not the iac. Hasnt acted up yet since I've changed the above.
Old 09-09-2012, 07:27 PM
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I'd say it was just the plug wire if it was melted. I've never seen anyone about spacing the coil off the head but I do know the ICM Cooling mod is quite popular and it was the one good decision the prior owners of my car made.
Old 09-09-2012, 10:13 PM
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That's what I'm thinking and hoping. But I haven't driven the car long enough to haven't act up. I'll update tomorrow. Thanks for the input.
Old 09-11-2012, 08:43 AM
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Turned out to be my opti harness. Since I replaced that the car hasn't acted up again.
Old 09-11-2012, 03:18 PM
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Default Did your Opti Harness look like mine?

The plastic crumbled when I disconnected my harness!

Originally Posted by slomaro91
Turned out to be my opti harness. Since I replaced that the car hasn't acted up again.
Attached Thumbnails LT1 Erratic Idle-opti_harness_01.jpg  
Old 09-11-2012, 09:32 PM
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Yikes. The clip on my old one snapped but something was eating yours.
Old 09-24-2012, 03:25 PM
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Turned out to be a defective opti. Lasted 1000 miles and crapped on me.
Old 09-24-2012, 07:08 PM
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Originally Posted by slomaro91
Long time lurker here and current member over on Thirdgen, I'm a college student at Lewis University working on my Airframe & Power Plant Certificate and Business Degree, so I'm very hands on. Thanks in advance for all the help.

Scott
I commend you on striving to earn a A&P license. Personally I couldn't recommend working for the airlines to anybody. Hopefully your goals will lead you into other areas of this business.
Good Luck to you.

Tom



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