I got my car back last Friday(02/09/07), after getting my longblock replaced. While the engine was out of the car, I had the dealer install some headers.

The car seems fine, for the most part. I'm still babying it, keeping it around 3k rpms max, and no more than about 20% throttle. The car behaves like it always has, except for when I decelerate and clutch-in. When I do so, the rpms drop to ~200, almost to the point of stalling. It hasn't stalled yet, and I don't think it will. Nevertheless, it's annoying.

I have a hunch it's a leak. With the motor being out and having everything reinstalled, it could be any number of things. It could be my stillen airbox, a dirty or faulty MAF, a poorly aligned MAF, a leak somewhere between the MAF and the throttle body, a leak somewhere along the plenum, a leak on along the new header flanges, or a leak between my test pipes and headers.

So my first question is does my RPM issue sound like it's related to some sort of leak? I'm inclined to think it's some sort of unmetered air entering the system after the MAF. If it is a leak, what is the likeliest candidate?

I haven't opened the hood and tried to listen for a leak yet. And I can't hear anything like a leak while driving.

Suggestions please.

 

TB needs to be recalibrated?

 

I don't think exhaust leak will contribute to stalling; it is more like intake leak that contributes MORE to stalling

 

As stated above, it's most likely not an exhaust leak. Leaks at the header is pretty dang noticable and leaks in the exhaust aren't much of a problem unless they're major and if they're major, the noise is usually raspy and very loud. I suggest undoing all the connections with the intake, loosen, then retighten. Look for crimped gaskets (especially the one between the MAF and airbox. Also pay close attention to the intake pipe and ALL the connections. Undo them and reinstall. If that doesn't help, then move to the intake manifold. I'd loosen all the upper plenum bolts, inspect spacer plate, and reinstall. If that doesn't do it, then you're going to remove the lower manifold.

The fact that you're experiencing a slight stall when coming off of acceleration, makes me think that the leak is very small and really only causes issues on heavy vacuum. I think just a little adjustment is all it's going to take.

 

I had that problem when i got my plenum installed. I did the ECU reset and all that and it went away. But the car still idles lower than normal.

 

Saturday morning I completely removed the intake system down to the lower plenum. As I was doing so, I looked for visual gaps and tried to listen for leaks. I couldn't find any.

So I put everything back together. Whatever I did helped, a bit. The rpm drop when clutching in still happens, but not as often. It's only happened a couple of times in the past two days, whereas over the prior week it would happen every time. Also the rough idling has all but gone away.

Now I did notice a few things when I took everything apart. The upper and lower plenum parts were covered in oil. Some of it was old oil, but much of it was new oil. The bolts that extend through the middle of the plenum were extremely oily.

Also I noticed that there was dried oil sludge along the lower throttle body butterfly valve. I didn't attempt articulate the valve, so I don't know if it's collected on both sides.

How does one go about cleaning the throttle body? I know I can detach the throttle body from the plenum mouth. But should I be concerned with forcing it open while cleaning?

 

Just detach it and use TB cleaner that you can find from auto stores to cleam them from both ends of the TB.

For the extra oil, I dunno why then... but I recall last time that I have a stalling issue and a simple loosening all the upper and lower plenum bolts + retorquing them in the right sequence and torque + ECU reset solved the problem.

I was trying to narrow down to a single source that caused my stalling but.....oh well, G/L anyways