Hello I have had my 99 FRC for approx. 1 year and drove it to work yesterday morning for the first time. From start up to warm car idled very rough,for instance tach at idle jumped back and forth between 1.5 K to approx. 300 rpm.Now let me mention that yesterday morn the temp was 18 degrees.I don't drive car every day,normally weekends and days off.The plant that I work has smokestack that spews out very fine (supposed to not be acid water mist). Car has always idled pretty good.It usually varies at idle a little. I absolutely love car.A real sweet driving car. My question is would being so cold make car idle rough at first? Its not normally that cold here. Thanks rks959

 

Did you check to see if you're leaking air from the intake or air bridge? Sounds like you could have a leak. That variance in RPM's is pretty excessive even at 18 degrees.

 

I agree with checking for an air leak. Pull your codes and post. Also, if its in that environment as you mentioned, I would spray out the MAF.

 

The car was/is designed to run and idle smooth from first crank cold to shut down HOT. If your having an idle issue cold,,,it NOT normal. First things first,,,,,pull and check ALL the codes. You have a built in code reader:

READING YOUR Engine Diagnostic Codes (DTCs)

The Diagnostic Display Mode is entered with the following procedure:
1) Turn on the ignition but don't start the engine.
2) Press the RESET button to turn off any warning messages. (i.e. door open, trunk open etc…)
3) Press and hold OPTIONS
4) While holding OPTIONS, press FUEL four times within a 10-second period.

Initially, on-board diagnostics go into an Automatic Mode which shows diagnostic codes in a pre-set sequence: PCM - TCS - RTD - BCM - IPC - RADIO - HVAC - LDCM - RDCM - SCM - RFA. All codes will be displayed for each. ( i.e. PCM = 4 codes)
If none are present in a given module, you will see No More Codes on the display.
There are two kinds of diagnostic codes, Current and History designated with a letter suffix, C or ;H. A current code indicates a malfunction is present in the module displaying data. A history code indicates a problem existed sometime in the last 40 or 50 ignition cycles. When not accompanied by a current code of the same number, it's potential evidence of a previous problem, now resolved, that was not removed by clearing the codes.
More likely it's an indication of an intermittent malfunction.
Intermittent codes are the most challenging of the diagnostics. An intermittent code may have happened once, may have happened more than once but is inconsistent or may be happening on a regular basis but not at the time the codes are displayed. History codes can also be caused by a current malfunction in a system that is not operating at the time codes are displayed. An example is the rear window defogger which doesn't operate until the Body Control Module detects engine rpm. For history codes set by a module that does not operate with the key on and engine off, a special diagnostic tool called a Scan Tester is necessary to properly diagnose the malfunction.
Once the system has displayed all modules, it goes into the manual mode which allows selection of each module using combinations of Driver Information Center buttons. Manual mode can also be entered during the automatic sequence by pressing any button except E/M. Once the display shows Manual Diagnostics, select a module by pressing the OPTIONS button to go forward or the TRIP button to go back. Once a module is selected, a code is displayed, and if more than one are present;
press GAGES to go forward or FUEL to go back.
To exit the diagnostic mode at any time, press E/M. If you want to erase codes in a given module, press RESET
To reset the codes once in manual mode, press and hold RESET until it displays NO CODES Press OPTIONS to go to the next module. Repeat the steps until you have reset the codes in all the computer modules.
NOTE!! Only reset the codes IF you want to - it is NOT necessary to do this. Clearing a code does not repair a problem. You are simply erasing the evidence of it in the module's memory. If you clear the code/s, and extinguish the Check Engine Light, your emissions status ready will NOT allow you to pass an emissions test until you have completed the required driving cycles.
Once you have the codes, the next question is: What to do with the information?
First, consult the factory service manual. Any serious C5 Do-It-Yourself owner should invest in the Corvette Service Manual of the appropriate model year. The Service Manual is really a requirement if you want to understand and work on your C5.

Here is very good site of DTC definitions:


http://www.gearchatter.com


Make sure to include the H or C suffix!!




Read and post the DTCs

BC

 

Just by chance, please look at the coolant temperature when you turn on the ignition, both analog and digital. That particular sensor has a lot to do with the mixture controls in the PCM.