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Old 03-13-2009, 07:21 PM   #1
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Default 95 firebird Lt1, rough idle trouble shoot?

I have a firebird that just recently started idling rough when stopped and when accelerating. On start up prior to the recen rough idle the car will sometimes idle very low and shut off immediatly or within a few moments. But sometimes the car will start up right away with no problems just the rough idle now. and the car sometimes starts up at a slightly higher than normal idle. once the car picks up speed it accelerates alot smoother but you will notice the roughness when cruising around 50mph-60mph and you lightly press the gas. I was thinking the MAF sensor ? my dad is pretty ademit that its the O2 sensor? any ideas? and also the car is giving codes most of the time but becuase i have an OBDI computer with OBDII connection the shops i have taken it to have not been able to read the codes and autozone is by california state law supposebly not allowed to scan vehicles anymore?
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Old 03-13-2009, 07:23 PM   #2
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I would check for any vaccum leaks on the top of the motor. And although it prob is not something you wanna hear, but certainly sounds like your opti going. Make sure your spark plug wires are all good and not arcing. Etc.
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Old 03-13-2009, 07:33 PM   #3
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yeah def not somehting i wanna hear but have unfortunately been there and hear this. i took out the distributor about a month back and replaced it but not the cap and rotor i cleaned up the rotor and it looked good and as for the cap i did a retard move of lightly sanding down the small burn marks on the tips where it didnt seem to be getting connection from the ohometer and a buddy told me that wasnt a good idea because i could have made some uneven and they may not get connection properly. needless to say the car has run properly and performance wise has been good but the start up issue where it would sometimes idle low immediatly has slowly gotten worse since the reinstall day.
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Old 03-13-2009, 07:35 PM   #4
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and about the vacuum leak the only thing i could see on the top of the motor that looked like a vaccum was a hose going from the valve cover to the throttle body. It was split at the connection i fixed it and it didnt seem to make a difference?
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Old 03-13-2009, 07:35 PM   #5
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Well a new cap/rotor shouldn't be that bad if you know the optical part is new.
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Old 03-13-2009, 07:52 PM   #6
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Btw not that i dont think its the cap and rotor are the more then likely cause but what made you think of that instead of the MAF sensor?
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Old 03-13-2009, 07:55 PM   #7
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The stock MAF shouldn't really go bad, if you want to make sure, run the car with it unplugged speed density mode. That should rule out if its good/bad.
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Old 03-13-2009, 09:54 PM   #8
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hey i tryed disconnecting the plug to the maf sensor and started the car but there was no difference?
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Old 03-14-2009, 01:26 PM   #9
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Low rpm misses usually come from 2 things. A is clogged fuel filter or bad gas, this will also cause poor shifting in an auto car. B as was mentioned to you before the o2 sensors are going bad.

This could be an easy fix. There are ways of getting the codes read. They would help a ton.

Did you unplug the MAF while the car was running and there was no change? If so your ENG sensor fuse under the hood is blown or your maf is dead. If the fuse is good and it still made no change if you unplugged the maf while running you need to probe the pink wire going in to the MAf harness and make sure it has 12v power coming in.
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Old 03-15-2009, 02:55 AM   #10
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i just changed out th damn optispark and it was the problem the car still dies immediatley upon start up and to keeo it on i have to hold down the gas ? ?
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Old 03-15-2009, 03:02 AM   #11
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i ment it WASNT!!! the problem the car still starts up and dies immediatley ... i also tried a new MAF sensor and it wasnt the problem??/? please help?
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Old 03-15-2009, 12:19 PM   #12
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Read my previous post. Check the fuel pressure. I already directed you away from the opti.
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Old 03-16-2009, 01:14 PM   #13
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you need to read the codes the car is giving you or else you are just going to keep replacing parts and crossing your fingers....
since you can't get it scanned at autozone etc...
1. get an ALDL to USB cable- www.aldlcable.com. They sell the proper one that can hook up to a 16 pin obd-1 car. Cable is around 60 bucks or so.
2. Download a program onto your computer called freescan (like the name implies, it is free).
3. Hopefully you have a laptop, if not it's time for the desktop to take a field trip out to the garage
4. Hook computer to car w/ALDL cable
5. read codes
6. profit
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Old 03-17-2009, 01:14 AM   #14
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i checked the codes and the mass air flow sensor and the coolant level sensor came up. i put my buddies mass air flow sensor in the car the other day befoe i replaced the optispark hoping that it was the problem but nothing changed?
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Old 03-17-2009, 12:44 PM   #15
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Quote:
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i checked the codes and the mass air flow sensor and the coolant level sensor came up. i put my buddies mass air flow sensor in the car the other day befoe i replaced the optispark hoping that it was the problem but nothing changed?
i'm fairly certain the coolant level sensor doesn't throw a code, my low coolant light has been on since i bought my car (still haven't unplugged the sensor) and no code comes up for it when scanned. You may be referring to a coolant temperature sensor code, codes 14 and 15. Sounds like a tiny insignificant sensor, but our cars will run like crap if the coolant temp. sensor is not giving an accurate reading to the pcm, especially at startup. I would double check the code you got and replace the coolant temp. sensor if you get a code 14 or 15.

also, did you clear the codes and re-scan after installing your buddies MAF sensor to see if the MAF code went away? If the MAF code is still present after installing a known good MAF, your issue may be in the harness/wiring and not the sensor itself.
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