Okay, so I've had my Z28 for about three weeks now.

The behavior I'm about to describe doesn't happen all the time, but it seems to be a majority. I haven't tied it with any certainty to any other variables.

When the shifter is in neutral (or the clutch is in), I can blip the throttle, and the revs will stay up there for 1-2 seconds and fall off slowly. My expectation is that the revs will begin to fall relatively quickly immediately after I let off.

Likewise, engine braking is largely ineffective. I can coast at 40mph in 2nd and hardly lose any speed at all. A buddy of mine with an '01 WS6 M6 drove it for me and confirmed that the behavior is not normal for these cars.

Anyone have any idea why it might do that?

-Jake

 

no idea but id like to know aswell cause my car does the same thing

 

Interesting... we have the same set of mods -- a lid and a cat-back. I still have my cats, but this could still mean something. Do you suppose?

 

my car did it before i got the lid and the exhaust so idk maybe were just as unlucky as eachother lol

 

Got it. I bought my car three weeks ago with all the mods done already (except CAGS disable -- I did that last week), so it's good to know that's not the cause.

 

I've always heard the slow de-revving (whatever) is how GM programmed our vehicles. If they didn't make it drop slowly, the computer might freak out and stall the car, or something like that? Also heard it helps when racing, as the RPM will stay up a little more.

 

Whoever you heard the "helps when racing" thing from is full of it. A true race car will drop revs almost immediately.

I've found that my upshifts are faster than the revs can drop off, and I have to feather the clutch coming into every gear (you can even feel it coming into 5th and 6th if I work the clutch normally). This is bad, and I'm sure that if it keeps happening, I'm going to wreck my tranny mounts.

Remember that I said it only does it some of the time. When it's not doing it, the car is easy to shift and I can drive it very smoothly.

I'm going to swing by the Chevy dealer sometime soon... I'll let you guys know if they come up with anything.

-Jake

 

Mine does the same thing, and I think it's emissions related. If the revs drop off too fast, the emissions are greater, although that defies common sense. I think it has to do with unburned HC. Yah, that's proably it, you back off the gas, the vapors don't get catalyzed, and hydrocarbons get dumped out the exhaust. That's my take on it, anyway.

 

Mine does the same thing, but I noticed that it only does it if I have the HVAC set to defrost, no matter what speed or temp. Not only does it stay up, but it will actually slowly rise. But, if I put the HVAC on a differant setting, it never does it. In fact, if I do it in the middle of the surging, it immediately stops. Try it out and see if that is one of the conditions you have to fulfill too.

 

Mine did the same thing, and it was fixed with tuning at Futral Motorsports through the mail. Several folks didn't know what it was, but he did. I donno if I'd spend the money now, but if you ever get any more mods and want a mail order tune I'd call 1-877-78-4fast and inquire about getting a tune and tell allan/candy your problem.

Thanks,
Josh

 

check for any leaks in the intake, behind the throttle butterfly..

That was my problem, the egr was leaking.. however I see you have an 02 so you would not have an erg.. maybe somewhere else.

 

BTW, have you had a chance to see if it only happens with your defrost on? I was wondering if you have the same symptoms as I do.

 

I dont know if our cars even have one, im sure they do, but I have a grand cherokee that had the same problem about a year ago and it was a problem with the TPS (Throttle Position Sensor). The sensor was thinking that my throttle was pretty much fully open when it was just idleing. If there is any way you could hook a computer up to it, it should throw a code if this is the problem. Not the cheapest part to replace either, for as small as it is. Hope this helps.

 

Mine does it regardless of the defrost setting.

I think I have means to check my TPS output while I drive... I'll look into it.