My 89 IROC runs very rough and splutters through the intake under accelleration when cold. Kinda like a older car with a carb with the choke too loose. When it warms up it runs fine. I checked the codes and didn't get any and it's showing no lights either. Any suggestions on where I should look first? Thanks

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2000 NHRA Edition T/A
Pewter Metallic
A4 3.23 Gear w/GSC's
Whisper lid, MAF Ends, Ram Air Kit, Exhaust C/O
Best 60ft:1.94
1/8th:8.381@86.03
1/4:12.963@108.44

1989 IROC-Z 5.7 Duel Cat
Auto w/3.27 gears
Jet Stage 2 chip
Modified Air Box&MAF
AFPR&Air Foil

 

it could be a coolant sensor.

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1991 banditt2 #130 of 600
Project 350 TPI Banditt II
http://www.street-dawg-racing.cityslide.com
www.gcfba.com (Greater Cincinnati F-Body Association)
http://www.cincyspeed.com/

 

I agree with the above, but you should borrow a scanner and grab some data when the car is cold to make sure (look at the coolant temp the computer is getting). There are other things that can cause problems. A lot of the time sensors and relays are the culprit.


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Mike Metzler (Desert86Roc)[*] Check Out:SpeedWorldMotorplex.com[*] Check Out:Chevrolet F-Body Online Part & Illustration Manual[*] My 86 IROC 305 TPI Page (406 build in progress)

ET's @ 1250 ft[*] 14.28 @ 95.461 mph (uncorrected, NOS, no headers)[*] 15.362 @ 88.238 mph (uncorrected, headers, no NOS)
<><

 

I would also tighten all of the intake bolts. They have a tendancy to loosen over time and may be a pinhole leak until the intake pieces warm up.

Sounds stupid, but tighten 'em anyways.

 

I might also look to the timing too. When in open loop, some things don't kick in yet. How old is the module?

 

Thanks for the replies, I have another TPI motor laying around so I'll change the temp sensors and the module since neither have been changed since I've owned the car (about 5yrs) Someone mentioned the O2 sensor could be bad also. What do you think?

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2000 NHRA Edition T/A
Pewter Metallic
A4 3.23 Gear w/GSC's
Whisper lid, MAF Ends, Ram Air Kit, Exhaust C/O
Best 60ft:1.94
1/8th:8.381@86.03
1/4:12.963@108.44

1989 IROC-Z 5.7 Duel Cat
Auto w/3.27 gears
Jet Stage 2 chip
Modified Air Box&MAF
AFPR&Air Foil

 

I doubt it's the O2 sensor because the computer ignores the O2 until the car warms up.

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91 Z28
Come see The Vicious...

 

That's what I thought but I'm ready to try anything right now.

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2000 NHRA Edition T/A
Pewter Metallic
A4 3.23 Gear w/GSC's
Whisper lid, MAF Ends, Ram Air Kit, Exhaust C/O
Best 60ft:1.94
1/8th:8.381@86.03
1/4:12.963@108.44

1989 IROC-Z 5.7 Duel Cat
Auto w/3.27 gears
Jet Stage 2 chip
Modified Air Box&MAF
AFPR&Air Foil

 

Hey Dano U didnt fix this yet, its obviously something in the computer department, because the computer is compensating for it when it goes into closed loop.

 

I'm working on it right now....at 1:22 am.
I'll know later today if I got anywhere.

 

Check your TPS voltage and adjust it if necessary.

The TPS acts like a "accelerator pump" on a carb does, if you're familiar with that.

It's worth a try anyway.

 

If all that doesn't work, test the fuel pressure. You said you were willing to try anything.

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Later,
Vader
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Justice and Freedom will Prevail

 

Also check and make sure the timing is set to the stock 6 degrees.

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1991 Camaro Z28
5.7L 5-Speed (originally 305)
317 RWHP, 418 RWTQ
13.23 @ 107.62 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Member: SoCal F-Bodies
-=ICON Motorsports=-

 

my car does the same thing, it starts up idles at about 800. and when i start to accelerate if feels kinda like its gonna stall then it catches and takes off fine. fuel pressure is about same as when warm. about 44 PSI. but it ONLY does this when the outside temp is less then 80 or so. as when it was 90+ outside in the morn is was perfect. so could it be the Air Temp Sensor?

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- David
88' GTA 5.7L TPI MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass, Gutted CAT, Flowmaster 80 Series

 

I had the same problem with my '88 IROC. It may be your MAF sensor. I disconnected the old MAF on my car and it ran fine (this turns on he SES light and activates the "Limp home" mode of operation).

After consulting the "Howell" TPI service manual, I then replaced the MAF (very expensive!) with a new one and it cured my cold start problem.