NVetro

Hey all, I have a few threads going but nothing specific to this new issue im having. My new 383 which i swaped in this past weekend is running GREAT, it idles perfect but I am having a small issue. She idles dead on at 900rpms, i rev her she comes right back to idle. When I take her on the road she drives fine from what I can see, but when i come to a stop sign or stop light she dips past idle (which is set for 900rpms) and goes to about 550/600ish rpms and almost dies she doesn't come back to idle. Most of the time if i leave her there chuging at that rpm the pcm will bring her backto idle, but sometimes she will die, I guess cus the rpms are sooo low. I have a datamaster log in both UNI format (which is inside the .zip file and i also converted it to csv for all you people without datamaster) I am not throwing any DTC codes and do not have an ses light lit, what did happen when I was driving around was interesting...I stoped at a light and she dipped below idle and was chugging barley running and the ses light came on, i looked at the dtc code that poped and it was MAP volt high or somehting along those lines, when it went back to idle, and the ses light went away. Here are the things i have checked and some info:

*Fuel pressure is at 43 psi at idle
*Tried a friends MAF which i know is working
*Drove it around to let the pcm try to learn
*Checked for vacuum leaks (NONE)
*As you can see im getting some false knock from the vpipe and headers, i uplaoded a tune with the knock sensor detuned for testing purposes and still the same thing. This is not a tuning issue nor a timing issue
*Disconected the tps sensor and set the idle screw on the holly 58mm tb to match the pcms idle.
*All sensors sare brand new and all reading data via datamaster

any ideas???

http://www.webideas.net/94transam/da...83chrismaf.zip

and here is is in csv format for those without datamsater

http://www.webideas.net/94transam/da...83chrismaf.csv

jsetzer

How big is the cam? Vacuum is always an issue.

I can't look at your file right now, at work. But how are your IAC counts? Are they pegged at one extreme when stopping?

SStrokerAce

The Holley TB ain't the best thing i've ever seen, it could easily be that POS.

What was the EXACT DTC?

Bret

ulakovic22

Crack the throttle blades open a little bit until it goes away. I had the same problem a while ago. The IAC can't open fast enough to compensate for the airflow loss from the blades closing. You can drill small holes in your blades or just crack them open a little with the idle adjust screw. 5/16 allen wrench IIRC.

Gripenfelter

I just had this problem. I can't view your file at work but if your IAC steps are pegged then you aren't getting enough air.

I drilled the center hole, in the front of the TB above the IAC and below the blades, a little bigger. I had to go 3 drill bit sizes bigger. Start with 1/32 bigger. Stop when your problem goes away.

Injuneer

Link to the .csv is not working.

NVetro

sorry csv link works now, check her out. When you guys can you'll see what i mean, its a good log, idling, driving around town and such, getting on her alittle. You'll see what i mean when idle drops to 400ish 500ish at times via the graph.

Sstrokerace: The EXACT DTC is, MALF 33: MAP HIGH.

NVetro

hmm you guys are right about the IAC thing i think. I was looking at an OLD datamaster log when i had just bolt ons on my lt1 and at idle the IAC position was like: 10,11,12, etc... My 383 at idle is reading about 120ish, DONT be confused though, my car is idling GREAT with the 383, its when i come to a stop when driving is when it dips below the idle to 400/500ish rpms and wants to die until the pcm brings it back up, i rev it to bring it back up, or it dies. So what do I have to do? Drill the IAC hole bigger????? I've never heard of this... ALSO if i crack the blades open by adjusting the screw on the throttle body that will also increase the idle and the tps % no?

NVetro

anyone? I'm leaning toward an IAC issue. How can I rectify this....Injuneer what did you do? Your running the same TB.

Injuneer

Opening the blades will not increase idle speed. It will TEMPORARILY, until the PCM closes down the IAC counts to bring the idle back where it belongs. That's the whole purpose of opening the blades up more- to get the IAC motor position back to where it can control the idle speed.... BOTH at true idle, and when slowing down.

Opening the blades more will increase the TPS voltage. As long as it doens't go over 0.90V it won't cause a problem. You can also slot the screw holes in the TPS sensor so you can lower the voltage, if that's the problem.

I'd say to open the blades more, verifying that the idle counts have come down, and that the TPS voltage is still in the correct range. Then drive it and see if its solved the problem.

NVetro

ok, I will try that today....does it matter if i get the tps volts to .90 but the tps % is at 1% or something??? I REALLY dont wanna slot this thing if i dont have to hehe.

-Nick

CrystalSS

The stock throttle body has a small hole drilled between the blades in the iac passage, this lets air directly into the plenuum, my Holley that I just installed did not have this hole. The air that flows through this hole is not metered by the IAC, its a bypass. It was like 3\16 same as stock TB. This did not fix my problem...... but may help your stalling issue? I am surprised that you do not have a sticking problem.
My problem was sticking blades only when the car was running, I did not have a problem with the idle or stalling, to prevent sticking I have to keep the idle screw out far enough that it idles around 1200 rpm, even though set point is 950. I assume that my IAC is closed and cannot bring idle down any more.... need to get a scanner!
Other people have fixed split blm's by drilling 7/64 holes in the blades, it helped the idle.

SStrokerAce

I think you found your issue...

IAC counts are too high so the IAC can't control the idle smoothly because it's already way to far open....

Now if you open your throttle blades more then you have the issue of a high TPS....

So that means you slowly increase the size of the hole in the throttle plate. Or put ONE in on ONE side of the TB until the IAC counts go down and the TPS voltage is correct. That should solve the problems.

Bret

NVetro

I'm not following Bret, your saying drill a hole in the red butterly's? Also, EVERYONE is talking about idle. The idle is perfect guys,there is nothing wrong with it, it runs and stayed idled like a stock lt1. My issue is only happening when im driving the car and coming to a stop, the rapid closing of the blades (when i come to a stop light) is causing my issue it seems, like you all said, the motor cant get enough air and adjusting the stop screw will only increase my tps volt and %. Just wanted to clarify. Ok Bret, go ahead :-)

String

The IAC controls the idle but also follows the throttle to a point. It does this so that the car does not die when the throttle is abruptly closed. With your counts at 120ish you don't have enough room for the IAC to keep the engine running when you close the throttle. The counts should be aroun 30 to 40 and this will give plenty of room. There are only a couple of ways to get the counts down. Open the blades or drill holes. I drilled holes, starting at 1/8 and went until the count came down. Now the car idles great and returns to idle great, no stumbling or dying. BTW, I also have a 383 and the Holley 58mm. My problem now is I keep getting a code that the TPS voltage is too high. When I checked the throttle % goes over 100. I am going to do a search and figure this out.