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Tunning issue with the C5r427. What do you all think? TPS? PCM tuning? vacumm leak?
I plan to remove and reinstall the F.a.s.t LSX intake with new port seals. If that doesn't fix, I'll take it to a tunner.

She want to idle at 2000 unless I come to a complete stop, then it drifts down to 950rpm.
 

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Tuning.
Usually takes adjustment to the VE table to take care of hanging idle, also the throttle follower table.
With the greater amount of air via the FAST the maf can't make the adjustments to the VE table properly.
 

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This happens to my 346ci car every now and again. Usually on a hot day and after a some putt-putting through traffic.

If I get on it for a short distance and then just slow down off throttle but leave it in 3rd and coast to a stop, the car hangs at 2000rpm - even if I come to a complete stop.

Normally I need to to place a slight load on the engine to bring the idle down. (by place a load, I mean slowly let out the clutch while standing on the brakes to get the idle to come down with the load)

This happened before and after my MTI tune.
 

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My car does the same thing and I cant stand it. :flaming: Hopefully when I get the car retuned by a different tuner things will be better.

George
 

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I agree with Tom ... this is why a good tuner will do a dyno AND a street tune. My tuner rode with me for over an hour getting the street manners dialed in, including such things as the "hanging idle" problem you describe.

Les


FRC Tom said:
Tuning.
Usually takes adjustment to the VE table to take care of hanging idle, also the throttle follower table.
With the greater amount of air via the FAST the maf can't make the adjustments to the VE table properly.
 

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I bet its the running airflow table. That has to be tweaked when alot of free-er breathing mods are added to the engine. Especially h/c package.

Dixit
 

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georges03zo6 said:
My car does the same thing and I cant stand it. :flaming: Hopefully when I get the car retuned by a different tuner things will be better.

George

I had the same problem, I went back and he fixed it :D

It's sweet now :thumb:
 

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Well - my car has always been prone to this behaviour on hot days - even when stock - so what is the real reason and answer?

It doesn't happen often, I would say about once a week - in hot weather if I get on it after being caught in slow movign traffic - so I just avoid the circumstance that induces the behaviour when ever I can.
 

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RC45 said:
Well - my car has always been prone to this behaviour on hot days - even when stock - so what is the real reason and answer?

It doesn't happen often, I would say about once a week - in hot weather if I get on it after being caught in slow movign traffic - so I just avoid the circumstance that induces the behaviour when ever I can.
Would you happen to have a blackwing or a Stinger, Paul?

I allready gave the real reason and answer. I didn't make this up or just read it somewhere. I'm not a keyboard mechanic.
I tune cars for a living.
 

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ZO6/Les said:
I agree with Tom ... this is why a good tuner will do a dyno AND a street tune. My tuner rode with me for over an hour getting the street manners dialed in, including such things as the "hanging idle" problem you describe.

Les
Tom is right on the money with this one! My car did the same thing after I installed my H/C package, but Tom spent some time with me driving around and scanning with HP Tuners, and got it dead nuts on the money. My car runs perfectly no matter where it is, at sea level or here at 7550'.
It all in the tuning! I've got a damned nasty cam in my car, and its street manners are great thanks the FRC TOM!

:thumb: :thumb: :thumb: :thumb:

Jim
 

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FRC Tom said:
Would you happen to have a blackwing or a Stinger, Paul?

I allready gave the real reason and answer. I didn't make this up or just read it somewhere. I'm not a keyboard mechanic.
I tune cars for a living.
Oh - I don't doubt your prowess Tom, and have ultimate respect for your knowledge and contributions ;)

My question was in context of a basically stock car (not H/C or extra cubes :)) - and you are correct, my car had the Stinger on when it first displayed this behaviour? :)

I had taken the answers in their literal sense as being about more radically modded cars.

-Paul
 

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RC45 said:
Oh - I don't doubt your prowess Tom, and have ultimate respect for your knowledge and contributions ;)

My question was in context of a basically stock car (not H/C or extra cubes :)) - and you are correct, my car had the Stinger on when it first displayed this behaviour? :)

I had taken the answers in their literal sense as being about more radically modded cars.

-Paul
:coo: :coo:
Most likely you also removed the screen in your MAF.
2001 mafs are scaled differently then the '02-'04 screenless mafs. The engine runs off the VE table which is calbrated with the stock filter system. The maf is used to make any necessary changes in air volume for whatever the cause.
Any changes in airflow from stock will not be what the stock table is expecting and the maf makes the changes needed.
Sometimes these changes are out of the maf's range to adjust. The proper way to fix this is to change the expected air volume in the VE table.
In an open filter such as the stinger or blackwing when you are slowing down to a stop in gear it's getting more air than a closed filter like the VE table was calibrated for. A closed filter stock, or even one with a box over it will have a consistant amount of air that the maf can make the adjustments with. The open filter's air is way more varible and sometimes the maf can't react fast enough. Doesn't happen with all cars but this is why it happens.
In your case since there is no cam involved you can go into the throttle follower decay table and speed up the delay time it takes to close the throttle at low mph while in gear.
 

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Mine Too!

I have a 2002 Z that has been modified by Lingenfelter. Heads, cam, short headers, air etc with GLH magnums. It dynos at about 445 RWHP. 2 weeks ago the battery went completely dead, changed after 24 hours and the idle is sticking. Earlier in the week it was sticking at 2000 rpm, today at 1500 rpm. After a few seconds at stop the idle drops to normal of 900 rpm I have put about 125 miles on the car since the battery change.

Is the car relearning the correct idle or is it something else. Any information would be appreciated. Thanks
 

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wagssd said:
Is the car relearning the correct idle or is it something else. Any information would be appreciated. Thanks
Idle Relearn

Just drive it and it will relearn but if what ever mod you did is extreme enough that the car absolutely won't idle, then here is the correct procedure:

Manual Transmission:
1 Turn Off the ignition
2 Restore the PCM battery feed
3 Turn Off the AC controls
4 Set the parking brake and block the drive wheels
5 Transmission in neutral
6 Start the engine
7 Allow the engine coolant temperature to reach 176 degrees F (Or higher)
8 Turn on the AC controls (Omit for 2000-01 model)
9 Allow the engine to idle for 5 minutes (Omit for 2000-01 model)
10 Turn off the AC controls (Omit for 2000-01 model)
11 Allow the engine to idle for 5 minutes
12 Turn off the engine for 15 seconds
 

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I'm fighting with a 427 today that stays at 2000 rpms only with the air on. Does it only while driving.
I shut the AC off and it goes right back to normal. :-?
Car is perfect at idle with air on or off but as soon as you start to drive it with the AC it sticks at 2000.
I can be cruising in 4th at 45-50 mph and as soon a I hit the AC switch it goes into cruise at 2000, turn the AC off and it decels.
It's like I'm turning the cruise control on and off. I'm thinking it could be the throttle body, but why only with the AC on?
Yes it's got me baffled.

Actually I have 2 427s doing this right now both with fast intakes. One with a 90 mm TB and the other has a 95 mm TB.
 

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I have the Fast 90 and the 90 TB. It is either a vacum leak or in the tune. There is a setting for the hang time in the tune, (kind of like a IAC motor adjustment) on a manual (cable operated) TB set ups
There are TWO differant settings (A/C on and A/C off.)
I like mine hanging for 1 second at 1200 and the one bounce back to idle. With the Fast setup, I found that it took awhile for me to get that right.
 

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It's normal for RPM's to hang while the vehicle is in motion and is a function of the PCM. You can see it clearly if you watch the speedo while coasting to a stop...RPM's will hang until the speedo reads zero. I believe that feature exists to give you better off-idle response once in motion and to prevent RPM's from dropping too low during shifts. If the car is modded beyond bolt-ons, the parameters for that feature likely need to be tweaked.
 

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22655TD said:
I have the Fast 90 and the 90 TB. It is either a vacum leak or in the tune. There is a setting for the hang time in the tune, (kind of like a IAC motor adjustment) on a manual (cable operated) TB set ups
There are TWO differant settings (A/C on and A/C off.)
I like mine hanging for 1 second at 1200 and the one bounce back to idle. With the Fast setup, I found that it took awhile for me to get that right.
I carefuly read ever single table and the only ac on ac off is the initial idle setting. Maybe there is a table missing from HP Tuners that LS1 edit has.
I've tuned better than a 100 cars and these 2 are the only ones to give me this problem.
 
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