Slow returning to Idle? - Page 2

klaptrapper · 04-13-2010, 02:48 PM

My Corvette ZR-1 does the same thing. I am told on that forum, that it is done that way, and quite normal. I think it is done to alow the engine to rev more quickly after trailing throttle. The computer keeps the Idle Air Control stepping relay at that positioin until the car stops.It is much more noticeable on a standard transmission car,because coasting to a stop at a traffic light, for instance, the revs don't drop to zero until the vehicle stops.
My V is under wraps now, but this week, when I have it out again, I will verify that this car does the same. If my memory serves, my V does the same thing, therefore I did not find it exceptioinal and note it before.

Quote:

Originally Posted by BILLS_XLR

Hate to go back to the original topic but... Has any one experienced a hesitiation about 1200 RPM when decellerating. My throttle holds at 1200 while decelerating, with or without taping the brakes, with or without the AC on and with leaving it in drive or shifting to neutral. As soon as the speed (speed signal) goes to 0 the idle drops to 800 or so. Something is reading the 0 speed signal and dropping the idle. I have thoroughly cleaned the throttle body (that's another story) and checked for vacumn leaks with none found. The local dealer said this is normal on supercharged cars but I don't buy it! There may be some slight compensation for the additional air volume when the throttle first closes but but I don't think it should "high idle" all the way down to 0 MPH. Its definately effecting Gas mileage, brake wear and It could be considered a safety issue as simply llifting off the throttle does not generate anywhere near the engine braking effect that you would expect.

klaptrapper · 04-14-2010, 09:51 AM

Nope, took the car out this morning, if I kick it into neutral at say 15 mph, the engine returns directly to 800 rpm. it does not hang higher for any apreciable length of time. Seems you do have a problem. Still under warrantee??

Rusty

Quote:

Originally Posted by klaptrapper

My Corvette ZR-1 does the same thing. I am told on that forum, that it is done that way, and quite normal. I think it is done to alow the engine to rev more quickly after trailing throttle. The computer keeps the Idle Air Control stepping relay at that positioin until the car stops.It is much more noticeable on a standard transmission car,because coasting to a stop at a traffic light, for instance, the revs don't drop to zero until the vehicle stops.
My V is under wraps now, but this week, when I have it out again, I will verify that this car does the same. If my memory serves, my V does the same thing, therefore I did not find it exceptioinal and note it before.

onalaska · 04-15-2010, 05:58 AM

I have had my V out serveral times since your first post and have not noticed any delay with the throttle returning to idle. It sounds like the throttle plate is not closing as it should. On the V it's not in a good place to service unless you remove the supercharger.

BILLS_XLR · 04-15-2010, 06:55 AM

oalaska and KLAPTRAPPER thanks so much for answering my question, as it does now seem (as I expected) that this condition is not "normal". I'm going to try another dealer and twist arms till I get someone to ride with me and experience it first hand. I was beginning to give up on finding anyone who could try this with their V for a comparison, got a little scarey with this discussion turning to the number of gears in a given trans. It is NOT a sticking throttle plate as 1.) I thoroughly cleaned it and 2.) it always returns to idle (800) when revving the engine in neutral but will hang when in gear and decellerating, it cannot be a mechanical issue... it's electrical, as something is sending a "high idle signal" until a 0 speed signal is generated. . Thanks a million and I'll keep you posted.
Bill

onalaska · 04-15-2010, 05:30 PM

I'm amazed you were able to get to the throttle plate to clean it. It looks real tight back there. That is a strange problem, sounds like software causing it. Did it do it when you bought the V or did it start later?

klaptrapper · 04-19-2010, 12:30 PM

Bill, you will notice, that if you are using the manual shift, the trans clutch will remain engaged. Says in writeups I have read that is done so it will "approximate" a manual transmission. In what mode are you running when you do this???

Quote:

Originally Posted by BILLS_XLR

Has anyone experienced a very slow or lazy return to idle (800 or so RPM). After removing my foot from the accelerator the idle will solwly drop to about 1200-1300 RPM and stay there until I come to a complete stop. I can hear and feel the transmission flaring as it downshifts which is usually a symptom of high idle. Is there an aux air or idle valve that might be sticking or dirty. The local dealer tech says its "normal", I don't think so... does anyone have experience with this condition in a V,
Thanks,
Bill

BILLS_XLR · 04-20-2010, 09:10 AM

Quote:

Originally Posted by klaptrapper

Bill, you will notice, that if you are using the manual shift, the trans clutch will remain engaged. Says in writeups I have read that is done so it will "approximate" a manual transmission. In what mode are you running when you do this???

KLAP It occurs in all modes...."Normal" (in drive, automatic mode) "Performance" (you shift it, stiff shocks) and even if I bump it into Neutral at 40 MPH and coast to a stop. Until it sees a "0" speed signal it will not always return to curb idle. I'm meeting with another '06 V next week for a back to back comparison....I'll keep you posted. Bill

klaptrapper · 04-20-2010, 09:12 AM

Gocha! keep us informed on progress.

Quote:

Originally Posted by BILLS_XLR

KLAP It occurs in all modes...."Normal" (in drive, automatic mode) "Performance" (you shift it, stiff shocks) and even if I bump it into Neutral at 40 MPH and coast to a stop. Until it sees a "0" speed signal it will not always return to curb idle. I'm meeting with another '06 V next week for a back to back comparison....I'll keep you posted. Bill

onalaska · 06-10-2010, 06:42 AM

Quote:

Originally Posted by BILLS_XLR

KLAP It occurs in all modes...."Normal" (in drive, automatic mode) "Performance" (you shift it, stiff shocks) and even if I bump it into Neutral at 40 MPH and coast to a stop. Until it sees a "0" speed signal it will not always return to curb idle. I'm meeting with another '06 V next week for a back to back comparison....I'll keep you posted. Bill

Bill, what did you do about your idle problem? Might be related to your gas mileage issue.

BILLS_XLR · 06-10-2010, 09:24 AM

Klapp,
There is no question that the "high" idle condition is contributing to the poor mileage. Neither dealer was able to nail down a cause so they both determined it was "normal" which it obviously is not. That said, after speaking to a tech at D3, I've located a shop here that has experience with modifing ECMs on Corvettes and had also done some highly recommednded work on reprogramming an ECM in a V. I plan to visit them next.
And before any one wastes their time with thoughts or theories about a possible link to the transmission, I'm 100% positive that this is a software programming issue and not mechanical in any way.

klaptrapper · 06-10-2010, 10:30 AM

Please keep us all informed of progress going that route!!

Rusty

Quote:

Originally Posted by BILLS_XLR

Klapp,
There is no question that the "high" idle condition is contributing to the poor mileage. Neither dealer was able to nail down a cause so they both determined it was "normal" which it obviously is not. That said, after speaking to a tech at D3, I've located a shop here that has experience with modifing ECMs on Corvettes and had also done some highly recommednded work on reprogramming an ECM in a V. I plan to visit them next.
And before any one wastes their time with thoughts or theories about a possible link to the transmission, I'm 100% positive that this is a software programming issue and not mechanical in any way.