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Rough Idle while cold

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Rough Idle while cold

Old 03-14-2019, 10:22 AM
  #1  
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Rough Idle while cold

I have a 92 Camaro RS, 305 TBI 5 speed, everything is stock. When I start the car especially when its cool or cold, it idles terrible and will even die. It will run really rough and chug plus as the RPMs go up and down the volts will fluctuate until it warms up then it idles just fine. I've looked at the vacuum lines and didn't see anything obvious. So far I have changed a whole pile of things, if anyone has any ideas please share.

New
IAC motor
Rebuilt TBI (Gaskets, cleaned, and fuel pressure diaphragm
Air temp sensor
Fuel Pump & Filter
Coolant Temp Sensors, both the one for the computer and the one for the gauge
Water Pump, thermostat and radiator
Heater Fan
Doubt those last couple are important but thought id mention it
Caidhlaoch is offline  
Old 03-14-2019, 05:01 PM
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Re: Rough Idle while cold

Stop changing parts at random, connect a scan tool and look at the data stream. Might be worthwhile to read the codes while you're in there--but the data stream is more important.

How long has it been since you've checked the cranking compression, fuel pressure, and done a proper tune-up including testing plug wires, and verifying cap/rotor/spark plugs/ignition coil/timing etc.
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Old 03-15-2019, 12:31 AM
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Re: Rough Idle while cold

So, to clarify, this is a new to me car, I have only had it a few weeks. That said I changed the IAC because it looked like crsp and it's a 30 yr old car, I rebuilt the throttle body because it was filthy and the gaskets were falling apart when I took it apart. I replaced the fuel pump due to low and unstable fuel pressure, the fuel filter because I had no idea when it was last changed. I replace the air temp sensor because a previous owner discarded it and left the plug flopping around on top the motor. I replaced the coolant temp sensor because it was just lying on top on the intake and in its place bubba screwed in a cheap after market temperature gauge sending unit. I replaced the O2 sensor because it looked old and ratty and upon removal was badly corroded. I replaced the sending unit for the temperature gauge because it was not working. I overhauled the cooling system because it didn't have the correct radiator or thermostat housing. It also did not have a thermostat which I replaced And for peace of mind I replaced the water pump. So nothing I have changed has been "random". These were things it needed but as long the way I still have a cold start issue.

I have not checked the compression of the cylinders, it doesn't smoke or burn oil so I did not think to. The plugs, wires and cap all are in good condition. I've pulled codes and the only thing that comes up is VSS fault.

I will data log it and see what I get. I will post the results and hopefully someone who doesn't immediately second guess how I got the data or assume I randomly data logged for fun or did it improperly can provide insight.
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Old 03-16-2019, 07:58 PM
  #4  
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Join Date: May 2015
Location: Ohio
Posts: 205
Car: 1992 Camaro RS
Engine: L03 305 V8
Transmission: 700-R4
Axle/Gears: RPO GU2 - 2.73
Re: Rough Idle while cold

Originally Posted by Caidhlaoch View Post
So, to clarify, this is a new to me car, I have only had it a few weeks. That said I changed the IAC because it looked like crsp and it's a 30 yr old car, I rebuilt the throttle body because it was filthy and the gaskets were falling apart when I took it apart. I replaced the fuel pump due to low and unstable fuel pressure, the fuel filter because I had no idea when it was last changed. I replace the air temp sensor because a previous owner discarded it and left the plug flopping around on top the motor. I replaced the coolant temp sensor because it was just lying on top on the intake and in its place bubba screwed in a cheap after market temperature gauge sending unit. I replaced the O2 sensor because it looked old and ratty and upon removal was badly corroded. I replaced the sending unit for the temperature gauge because it was not working. I overhauled the cooling system because it didn't have the correct radiator or thermostat housing. It also did not have a thermostat which I replaced And for peace of mind I replaced the water pump. So nothing I have changed has been "random". These were things it needed but as long the way I still have a cold start issue.

I have not checked the compression of the cylinders, it doesn't smoke or burn oil so I did not think to. The plugs, wires and cap all are in good condition. I've pulled codes and the only thing that comes up is VSS fault.

I will data log it and see what I get. I will post the results and hopefully someone who doesn't immediately second guess how I got the data or assume I randomly data logged for fun or did it improperly can provide insight.
Hey Caidhlaoch,

I'm experiencing the exact same symptoms but I've got a project 92 RS 305/Auto I just picked up. To add insult to injury it gets 10X worse when placed in gear. No intention on hijacking your thread my friend. However i'm personally going to take Schurkey's advice to you first thing in the morning and tackle a a proper tune-up including ICM. I've never checked cranking compression, timing or fuel pressure on either of my 92's, but I'm willing to learn how and I just bought the Actron CP7838 fuel pressure test kit because fuel pressure seems to be a #1 question. While sometimes responses can come off abrasive I believe they're offering their input based on experience, and answering the same questions a trillion times, so try not to take it personal. I do not have the equipment to datalog, but look forward to you posting your results, maybe it'll shed some light for me in what to look for. I'm working through my issues using my GM Service Manual and i'm happy to post pic's of diagnostic aids, etc if you need.
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