Tuning! For GM vehicles

[LeanBurninating]

wait wait wait wait...

who remembers the part where he says the motor acted this way since it was new?????

[theunchosen]

I don't think he mentioned it was doing this since it was new. Although I can see that happening. I've installed parts out of the box and they are disfunctional, with either springs being too stiff or too soft. Also its entirely possible the spring has just rusted up alittle and in recent periods its gotten slower due to rust.

If its harder to pull down on the accelerator its rust. If its easy to push the accelerator down. . .its the spring.

[The Atomic Ass]

Originally Posted by LeanBurninating

wait wait wait wait...

who remembers the part where he says the motor acted this way since it was new?????

Since PURCHASED. It was purchased used.

[The Atomic Ass]

Originally Posted by theunchosen

It could just be that the spring for the throttle body is worn out. A quick fix would be to either grease or WD-40 the spring and the hinges for the throttle body. If you want to find out if this is the problem(you are going to have to pop open the hood to look around anyway. . .) just open up your intake tract until you get to the throttle body. Pull back the gas with the clutch in while someone else watches. The plate should snap back shut immediately after you release the gas meanwhile the rpms should cycle downwards rather quickly.

I predict what you will see is the throttle plate slowly drawing backwards. If I also had to guess I would say your engine doesn't quite shut off the GO when you let off the gas, but this might e masked under normal driving by the fact you are applying the brakes and not really paying attention to the revs then. less effective braking would be another sign of this(quick shift from accel to brake and its still throttle open acceling, while you try and brake).

Well, the throttle-body is not sticking, it snaps firmly shut. It's also not dirty, unlike my mothers Blazer.

And it does exhibit the same behavior under decel, the engine breaking is very soft to non-existent before it starts to actually drop.

[The Atomic Ass]

Originally Posted by Christ

Check the Idle Air Control Valve as well. If it's sticking (it's an actuator/solenoid) it will allow too much air to pass the throttle plate...

If I could find the damn thing I would. I see nothing on the throttle-body resembling an IAC.

As for your suggestion of data-logging, I have Autotap, (which only reads, it does not program, unfortunately), and most of the numbers seem normal... But then, GM provides no numbers for what is normal for most sensors in the service manual.

[almightybmw]

Don't know if all GM vehicles do this, but my dad's 496ci from '02 rev matches on upshifts. You shift the gears and without any throttle foot input it'll put the rpms right where it needs them.

Granted it might just be a thing of that motor, all torqued out and stuff. One too long slip shift and it smokes the clutch, takes a few minutes to cool back down so it'll grab again.

[LeanBurninating]

Originally Posted by The Atomic Ass

Since PURCHASED. It was purchased used.

ahhh you caught me. My mistake.

[theunchosen]

Thats interesting.

So you've already looked at the throttle body and it snaps shut after you release the throttle, but it continues to stay revved up. I'm not entirely sure how thats possible. The ECU is going to inject roughly a gram of fuel for 15 grams of air. . .and if the throttle is closed it just means you get the same power as you would at idle(it wouldn't rev high) but you inject a ton of fuel most of which gets burned in the cat. If the air isn't getting in somewhere somehow it won't stay revved up like that, you can't burn more fuel than air allows.

Next suggestion I think Christ already said, watch the throttle body after someone shuts it down and watch to see if it moves after they let up and after it "snaps" shut. If it twitches to a less open position the ECU is telling it to hold open for some reason or another.

[stevey_frac]

My cobalt exhibits this float, now that I think about it. I think it's poor mans rev-matching. If you leave it in neutral, but your coasting down a hill on the highway, it'll turn over at about 1700 RPM. But it idles at under 1000 if it's stopped. When you go to change gears, it dosen't fall flat on its face as soon as you take your foot off the gas. Instead it'll slowly fall, and it gives you time to get the next gear in, and take your foot off the clutch. Makes for smoother shifting, and less clutch wear.

[wagonman76]

The bare minimum I'm looking for in control is complete control over DFCO. I want the engine to PLUMMET as if it had run out of gas when letting off the throttle.

I built a map sensor modifier box. Doesn't seem to affect mileage one way or the other, but I have discovered something recently. If I increase the voltage it technically runs a bit richer and retards timing, hard to say for sure without other diagnostic aids. But with increased voltage it will fuel cut pretty much right away. Normally it is a rare occassion to get it to fuel cut.