Have a question. What would cause the idle to drop too low on engine rev-down? I've noticed a slight 'miss' or roughness in the idle of my '99 coupe and when I rev the engine (in park) and take my foot off the gas pedal, the RPM drops below normal idle speed and can sometimes stall the engine. If it doesn't stall the engine it will returns to normal (600rpm) in just a few seconds and holds it fairly well, with slight variance. The vette seems to pull normally during WOT and seems to run smoothly at cruising speeds. Just this low-idle speed coming to a stop or revvin' down is worrying me.

Thanks,
Coyote

 

I want to piggy back on this one I have the same problem.

 

To properly diagnosis any C5, you need to read all of the codes and then post them in this post. Once we are able to read the DIC codes, we can start helping you understand what the problem is. Without the codes, we would only be guessing. Here is how to read the codes:

Go to this web site and follow the directions. Once you read and write down all of the codes, clear them and see if that doesnt take care of your problem. If it doesnt. post the new codes that show up. we will need to know if they are History or Current codes.

http://www.stengel.net/diccodes.htm

As soon as you post the codes, we will get to work solving your problem/s

Oh yea, make sure that you post year, all mods and any receint work that was accomplished.

Bill Curlee

 

I checked the engine codes as suggested and I got the following:
10-PCM
--------
P1518-H : PCM to TAC Module Serial Data Circuit

For A0-LDCM and A1-RDCM
--------------------------
B2282-H: Battery #1 Fault DCM-LEFT
B2284-H: Battery #2 Fault DCM-LEFT
B2283-H: Battery #1 Fault DCM-RIGHT
B2285-H: Battery #2 Fault DCM-RIGHT

For B0-RFA
-----------
U1096-H: Loss of Communication with PCM (No SOH Message Received -RFA)
U1064-H: Loss of Communication with DCM (No SOH Message Received -RFA)
U1016H: Loss of Communication with IPC (No SOH Message Received - RFA)

Those are the codes. Would most of those have been thrown during my recent dead-battery incident? It shows them as being denoted with an H meaning it is something in the History (last 40 or 50 ignition cycles) and I doubt I've started my car more than 40 times since I had the battery crap out. Nothing came up as a "C" (current). Can I clear these codes to see if they pop up again? (or should I?)

More info: 1999 A4 Coupe, Blackwing intake, Borla Stingers and other recent work was the replacement of the PCM and BCM after the delco battery (#1) leaked about 2 years ago. I personally just replaced leaking delco battery (#2) about 2 weeks ago with an Optima (finally!). (I know.. my fault for not doing it sooner<sigh>). I don't know if the leaking battery did any real harm this time around. I've only driven my car about 15 miles since the battery swap.

Secondary note: I did notice the idle rpm was having trouble dipping too low then stablizing after the BCM was replaced by the dealer last time (apx. a year ago) but it wasn't bad enough to bother me. Of course, just recently, it the post said, it can stall now.

 

OOOOHHHH YEAAAAAAAAA!! Dead Battery most likley caused them for sure!! Clear them all and take her for a drive. I would drive at leaset 20-30 miles total and check the codes again.

While your driving it, please give me your best description on how part throttle and WOT feels. Look for misses and dead spots. My bet is that you have a vacuun leak.

I will get a better idea after the next code reading session.

Bill

 

Sonds like you need to do an "Idle re-learn" also

 

Mine did the exact thing. Come to find out it was the clamp that held on my smooth coupler. It became loose and air was bypassing all the sensors.

I tightened them down and it runs perfect now.