URPREY

We installed a 224/224 112LSA cam in my car a couple weeks ago. It idles fine, and drives fine, but when I let off the gas to stop, the idle drops to 375-450rpm, then idles back up to where it should be. I don't really want to drill the TB. Is there another option to correct this? The rest of my mods are in my sig

Scalpel

iTrader: (4)

Not getting enough air into the TB. Up the RPM by 50 RPMs till it goes away or drill the TB.

URPREY

If I increase the RPM, won't it require more air thus amplifying the problem? Is there a way with LS1 Edit to correct this?

Scalpel

iTrader: (4)

Not enough air = surging, too much air = hanging RPM (tach won't fall to normal idle without hanging for a few seconds) If you get hanging, back it down.

LSs1Power

iTrader: (5)

Im having the same problem. Mine is even worse. My car dies when i come to a stop. I have to heel and toe every traffic light which is annoying. I would like to know an answer for the same question other than drilling the TB. Would raising 50RPM helps in recover the car from dying? The RPM just go under 800RPM very easy if i didnt give it gas and stalls.

Cal

iTrader: (1)

What you guys need to do is increase the values in the Airflow Decay table. I recomend changing all the table values from 0 to 14 mph to 31. This problem is caused by the PCM over compensating; for those that understand control systems, it means the gain is too high causing overshoot. It's like someone learning to drive that moves the steering wheel too much and weaves all over the road.

Ragtop 99

iTrader: (7)

another option is to open the TB idle set screw by 1/2 to one full turn

Ragtop 99

iTrader: (7)

Cal:
All the values are less than 1.00 but you suggest using 31.9?

Are you suggesting that he modify all 3 tables?

purevilss

Cal, I see this helping the surging, but what will help with the RPM's hanging?

Cal

iTrader: (1)

I just sugested 31.9 since that's the max value allowed. The system isn't really designed to handle a racing cam, so you need all the dampening you can get. I would only modifiy the tables that address the problem area; for my car I only needed to change the "in gear" table.

Cal

iTrader: (1)

If the RPM's are hanging, you could try reducing the Airflow Decay values, but on my car doing an idle relearn cured that. Some say runing too much idle ignition timing will cause RPM's to hang with an A4, buy I have an M6 and haven't seen that problem even with an extra five degrees.

Cal

iTrader: (1)

IMO, it is best to adjust everything a little rather than try to completly compensate with one parameter. In other words, speed up the idle rpm, give it more air by drilling the TB, increase the idle timing a little (three degrees) and increase the low speed Airflow Decay. I haven't seen adjustments to the Runnng Airflow (idle air) do anything; if you watch on EFILive, the PCM just sets this at whatever it wants to anyway and pretty much ignores the table. Drilling the TB is the only real way to make sure the engine gets enough air, other than turning the TB stock screw which is very touchy.

URPREY

Thanks for all the information. I'll give those things a try

Ragtop 99

iTrader: (7)

It's pretty easy to do, except that the damn screw is not to access. It has the advantage of being easily reversed, unlike drilling the TB. Unfortunately I learned the hard way about over drilling the TB hole.

Jorday

Increasing the timing by 3 or 4 degrees in my car made the drivability worse. It caused the idle to hang and made the surgeing worse. I also think that it made the stumbling when coming to a stop worse slightly it seems like.

Another thing that drives me nuts is I can't get the car to start and stay running without me pushing the gas pedal a little bit. After a few seconds, it will idle.

theblur98ss

iTrader: (71)

I have the same problem jorday. I've started drilling my TB little by little and it's gotten progressively better each time. One more size and I should be there.

LSs1Power

iTrader: (5)

Can u please post pictuers of your TB now... I just wanna see how it looks like because i think i have to start drilling mine soon.

Cal

iTrader: (1)

Yeah I over-drilled mine also, really pissed me off! So I made a nylon bushing on the lathe that pressed into the hole to make it smaller again. That worked great, but then I found that with the A/C on, it needed still more air, so I wound up taking out the nylon bushing, and it was fine after all. The way to do it is use a set of machinist's numbered drill bits so you can step up the size gradually.

Cal

iTrader: (1)

You really wouldn't be able to see any difference in a picture, you're just drilling out the existing hole slightly larger. Few people ever need to go bigger than 0.250 inch. It's actually easier to start a second hole, much smaller than the existing one.

Cal

iTrader: (1)

Yes increasing the timing can do all of that. The benifit to increased timing is a smoother idle with less lope.