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Another 5.7 TPI idle issue 1990 IROC Z

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Another 5.7 TPI idle issue 1990 IROC Z

Old 02-13-2019, 09:25 PM
  #1  
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Another 5.7 TPI idle issue 1990 IROC Z

Hey guys new to the forums but not to the car world. Before you say use the search function, please know I have read everything I can on the issue and I'm beyond frustrated. I have a 90 Iroc 5.7 L98. I am having idle issues. The car cold starts and hot starts great. It revs to the moon without hesitation. The car has a small surge at idle and occasionally stalls when i put the car in reverse. It is totally random. I just finished restoring this car, and it is a 70k original mile car. I need to replace the tach board so its hard to tell what it is actually idling at. Sometimes it has a surge to it and sometimes it the car seems to idle a little high. Other times it seems to be fine. I don't get it. The idle tends to climb a bit when on the brake, so I'm not sure if there is a small vacuum leak somewhere.

So far i have replaced and set the TPS to 5.4.
Installed a new IAC
Installed a new MAP
Installed a new CTS (This seems to help out with the stalling. It originally seemed to have a miss as well but this seemed to clear that up a bit)
Installed new cap and rotor
Installed new plugs
Installed new pump and filter
Sprayed with carb cleaner for vac leaks as well as cleaned the throttle body
All injectors ohmed out at 16

Other than this idle issue the car seems to run great. Starts great hot and cold, and idles up fine when your on the gas. Seems to run great when put in drive, however sometimes the car just wants to die when you put it in gear. Im stumped, any ideas. I restore cars for a living, this car was built to sell and its a beautiful original car, I just don't want to sell it until i know its right.
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Old 02-13-2019, 09:47 PM
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Car: 1967 Camaro, 91 z28
Engine: Lb9
Transmission: M20
Axle/Gears: J65 pbr on stock posi 10bolt
Re: Another 5.7 TPI idle issue 1990 IROC Z

The spec for the tps is .67-.76 on speed density tpi. Have you tried a new icm ?
The stock injectors suck for this car multecs coils short out. Are your readings hot ?
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Old 02-14-2019, 01:47 AM
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Car: 1992 Z28
Engine: 383
Transmission: 700R4
Re: Another 5.7 TPI idle issue 1990 IROC Z

Have you replaced the fuel pressure regulator?
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Old 02-14-2019, 04:05 AM
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Car: 1985 trans am/ 1991 RS
Engine: 355sbc/ v6
Transmission: 700r4 automatic
Re: Another 5.7 TPI idle issue 1990 IROC Z

I don't know much but do you think the torque converter may be your problem?

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Old 02-14-2019, 09:45 AM
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Car: 1989 IROC Convertible
Engine: 305 TPI (F)
Transmission: 700R
Axle/Gears: 3.42
Re: Another 5.7 TPI idle issue 1990 IROC Z

I wouldn't touch the Multec injectors- yet. If you go to Bosch D3 or other you will need a custom tune- which may help anyway.

Did you spray the outside of the intake system for leaks?

Did you read ohms to ground from the engine block/heads/intake locations? This will check your grounds.
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Old 02-14-2019, 12:30 PM
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Car: 1989-92 FORMULA350 305 92 Hawkclone
Engine: 4++,350 & 305 CIs
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Axle/Gears: 3.70 9"ford alum chunk,dana44,9bolt
Re: Another 5.7 TPI idle issue 1990 IROC Z

Brake booster have a leak?
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Old 02-14-2019, 02:20 PM
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Re: Another 5.7 TPI idle issue 1990 IROC Z

Originally Posted by TTOP350 View Post
Brake booster have a leak?
worth looking into blocking the line to the booster if you can duplicate the issue. Sounds real random the worst drive ability issues to find.
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Old 02-14-2019, 06:49 PM
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Re: Another 5.7 TPI idle issue 1990 IROC Z

Ya I donít get it, I have seemed to fix the stall when but in gear with the temp sensor. From what I see it is happening once it goes into closed loop. I reset the TPS to around .69. The weird thing is once itís in drive or reverse it sits and idles great. Once itís back to park itís starts surging again and idles a bit high. I cant believe itís the injectors, it would stumble and search all the time. Iím going to drop a new distributor in it tommorrow and reset the timing, but Iím not that hopeful at this point.
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Old 02-15-2019, 12:11 PM
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Car: 1989 IROC Convertible
Engine: 305 TPI (F)
Transmission: 700R
Axle/Gears: 3.42
Re: Another 5.7 TPI idle issue 1990 IROC Z

Is your base timing rock steady or does it wander?
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