When I start the car it runs fine, idles good, no misses etc... But when I rev to a high RPM and let off the motor comes down to idle it dies and appears to be flooded, runs rough and smells of gas.

Looking for any clues to what is wrong. MAF or TPS? We changed the battery to make sure it wasn't some sort of voltage problem, no luck
Thanks for any help.

(C5, LS1, AT)

 

Stock or modded? Was it ok and then the problem hit out of the blue or was the car worked on before the problem started? Stock tune parameters or modded?

 

There are a couple things that you need to do to help narrow down the issue.

1. Check for any DTCs I will post the procedure below :

2. Clean the MAF and check the air-filter.

3. Look for vacuum leaks on any hose that connects to the intake manifold. Check the entire length of each hose, especially the PCV system hose and fittings!

4. Make sure that the Throttle Body and throttle blade are clean inside.

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!!







BC

 

Changed the TPS, ran fine at first but after awhile it wanted to stall/flood again. Checked the MAF and it's working fine. All the codes were because the battery was completely dead, nothing to point us to our problem.

Going to change spark plugs now...

 

Changed plugs, old ones were black as coal even though they aren't that old. Still sputters.

I think it is a purge valve. After messing with it, I'm pretty sure that's it. Putting the new one in in a bit.

 

WHAT,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, in the C5 world is a purge valve????????????


Fuel Tank purge valve???????????????? What brought you that that conclusion?

BC

 

evap.

 

Evaproative Emissions Canaster purge valve. The ONLY time that should give you issues is if you over fill the tank and the fuel gets sucked into the charcoal canister. The PCM preforms a test on the EVAP Emiss System and checks that valve. Normally, if theres an issue in that system, it will come up with a DTC

You can disconnect and plug the vacuum fitting for the purge line on the drivers side of the manifold just behind the TB and see if the issue clears

BC

 

Well it wasn't the valve. Issue still occurs. If we unplug the valve and let a little air out it runs fine so i don't know...

 

Unplug the valve and let the air out of what? The fuel tank?? If your fuelm tank is overpressurizing, it can cause issues. Try disconnecting the system from the intake manifold and leaving the fuel cap a little loose to prevent the tank from pressurizing/pulling a vacuum.

Bill

 

Well...
When you start the car, it idles fine. But once you rev the car to 3k+, once it hits around the idle RPM the engine goes too low of RPM and wants to cut out and die but barely stays running and eventually idles fine after 5-10 sec. You can smell the gas like it's flooding the engine.

Changed, MAF, TPS, spark plugs, reset computer, EVAP, checked gas cap...Not really sure what else to do.

 

We had a Lingenfelter aluminum intake and cold air installed years ago with no issues...Problem started in the driveway after a drive.