Yesterday, I noticed my '02 C5 'vert (33k miles) would "stutter" a little when starting from a stop. Then I found that if I held the brake for a second or two and tried to bring the rev's up, it was much worse, kind of like the rev limiter at 1500-2000rpm. However, as soon as I released the brake, the stutter would cease, the car would accelerate and shift normally. Full acceleration produced nothing unusual, but "power braking" from a stop would make it do it every time.
Also, I noticed my hiway fuel mileage suddenly dropped 5mpg, from 29+mpg at 71mph to 24+mpg. I'm in Florida, using 91 octane non-ethanol fuel, usually Sunoco, and Techron every few tankfulls. New fuel filter. Since it's summer and the rainly season, the car has only been driven about 250 miles in the last 4 months.
Could it be bad fuel ? transmission ? computer ?

 

May be O2 bad O2 sensors.

 

Wouldn't that throw a code if it was doing it that much ??
I didn't mention that we were coming home after an autocross. I think it started doing it just at the last run I made
I'll look at the DTC's again today.

 

bump

 

Same thing happened to me last night were you able to diagnose it?

 

Could be a misfire under load. Look at the CHECK ENGINE LIGHT when the car does the studdering thing.

Is it FLASHING??? If it flashes, it detecting a misfire. Examine the plug wires and see if they are properly connected and not damaged/cracked or burnt.

When the engine has the issue, IMMEDIATELY pull up the DTCs and see what pops up. If there are a LOT of old history DTCs, clear them and pull the codes whe the problem is present. Dont turn OFF the ignition before you read the DTCs! Read it in that active ignition cycle.

READING YOUR Engine Diagnostic Codes



The Diagnostic Display Mode is entered with the following procedure:

1) Turn on the ignition but don't start the engine. NOTE! You can read the DTCs with the engine running and or driving down the road but it can distract you. BE careful! Some DTCs clear themselves when you turn the ignition OFF!

2) Press the RESET button to turn off any warning messages. (i.e. door open, trunk open ect)
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 C code indicates a malfunction is present and active 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 English/Metric (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 and hold the RESET button 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. You can GOOGLE the DTC and also find information on it.




Here is very good site that explains the DTCs:


http://www.corvette-web-central.com/C5DTCcode.html


http://www.obd-codes.com/trouble_cod...d-ii-codes.php



Make sure to include the H or C suffix!!






Bill

 

It sounds like it's pulling timing. Get someone to data log the car.

 

I posted that two years ago. A couple of months after that, the misfire stopped. I was just about to change the spark plugs and wires. One of those mysterious Corvette things, maybe a fouled plug that cleared. I just turned 40,000 miles today.