99C5JA

I recently did a home port job on my throttle body and have had an idle issue ever since. When you hit the throttle the idle will stay at 1600-1800 for a few seconds, then fall to around 1100, and finally hunt between 900-1100. The idle is set to 950. I did a search on this and found some threads about adjusting the running airflow at 80-100-120. But the car does this whether it is moving or not. So I'm wondering if this is a throttle decay issue, as running airflow seems to affect the car only when its moving. I just got a copy of HPTuners and am wondering where I should start. This is a C5, so some of the f-body tweaks may not apply. Any help would be appreciated.

BONESTOCKC5

iTrader: (1)

did you remove the TPS?, if that is not set exactly the way you removed it, that may be you problem, of if the throttle blade is not seated properly. may need to check tps with blade pushed closed, with volt meter should be around 1.46volts. just a few ideas, if all checkes ok, go idle table and adjust

99C5JA

I did not remove the TPS.

furiouSS99

iTrader: (-1)

[QUOTE=99C5JA]I recently did a home port job on my throttle body and have had an idle issue ever since.QUOTE]

Stop right there. Obviously you damaged something along the way. If it was idling acceptably right before you did the home port job, it would idle properly after the port job (assuming you ported the throttle body correctly.) If you went too far and removed material around the throttle plate, or you blocked off your idle air bypass holes with some sort of putty and forgot to add a hole (or too small a hole), this would all lead to problems. Or maybe you got metal shavings in the IAC motor, who knows? Don't automatically assume its a computer/tuning issue until all the mechanical issues are worked out first.

99C5JA

I was careful with the port job. The blade still closes to where you can only see pin points of light around it. C5's don't have idle air passages or an IAC motor AFAIK. These symptoms are very close to those with ported throttle bodies who have adjusted the running airflow to correct (I'm just not sure RA is applicable here). I'm not saying that I could not have damaged something but I did 99% of the work hand sanding everything to make sure that I did not go into areas that I shouldn't.

Billiumss

iTrader: (11)

Hold the TB up to a light and see how much light passes through the TB blade, around the edge. If you see a lot of light, that's your problem.

Local guy here had the same problem, it was ported "too good" where the TB blade rests.

99C5JA

As stated in the previous post there are only a few pin points of light that come through the TB when closed. No more so than before I started.

Bink

You've increased the airflow and IAC sets the blade, by step values, in the Corvette. Your target RPM and IAC settings are no longer in synch. Scan your DES IAC and TPS% and you can watch them try to achieve the target settings...they will bounce around -> result is surging and higher RPM.Try reducing your IACs at 40*C and above. I doubt you've increased airflow more than 10% so I'd try reducing by IAC 10%. If it stalls out bump it up a little. FWIW. Hope this helps some.

joel

99C5JA

Thanks Bink! I will give it shot.

jlwz71

iTrader: (3)

Page BigTex in the truck forum. He has had the same issues with a drive by wire ported throttle body. He can shed some light on this.

gojo

iTrader: (12)

If you touched the ridge around the TB throat area at all, you would also have possible racing at startup and cruise effect issues. It's hard to tune them totally out.

deezel

BigTex did have some problems after porting. I think he switched back to a stock TB after having trouble trying to tune for it.

jlwz71

iTrader: (3)

Tex took out to much of the "tounge" I beleive in the tb causing to much running airflow.

Creed

I agree with Bink that the IAC and target idle are too far away from each other. I've got a bbk and can't really remember the stock unit but I assume the stock tb has an idle stop screw doesn't it? I wouldn't doubt if maybe you're not getting enough air at idle due to the idle stop screw too far closed so it has to adjust the IAC to compensate. Happend to me once anyway with similar symptoms, turns out my idle stop screw just needed to open it up a bit and then use a little locktite to keep it from moving again. Something to check anyway.