Injuneer

I'm not going to be at home until Monday. I'll check the WOT pull, but I'm pretty sure I watched the throttle position and only considered data lines that were at increasing or 100% throttle.

gaedbo

Ok Gary, I will do that. Thanks for the input. It might be a few days, because I hurt my lower back and it's a real push getting around right now. But for sure I will check it out.

gaedbo

Well, I checked a few things out. Injuneer, thru your suggestions I was able to find 2 places where the exhaust system was rattling. One was the contact of the tin heat shield that was making contact with the muffler. The other was a clamp that was making contact with the exhaust pipe up over the rear axle. The clamp was welded in place on the pipe, so it was challenging getting my cutoff wheel in there to get me clearance. The entire exhaust system is welded at each joint. As I would tap on them with my hand they would resonate the sound from up by the cat all the way back. I checked the motor mounts also, and they looked really good.

I checked the Throttle Body Blades. I removed the elbow from the TB and by visual it looked very good. To double check, I made a mark with a fine line permanent marker next to the blade. I removed the throttle cable to see if there was any difference. None. I took a measurement with my vernier from the TB housing to the blade. Then I backed off the throttle stop screw a 1/2 turn and checked the dimension. It only changed .002 to .003, so I am thinking it was almost perfect where it was.(Seems like there is a built in stop that if you were to keep on backing the screw out it would stop at the fully closed position ?) I turned the screw back in 1/4 turn and left it there (Figuring I would double check it with Scan94/95 and adjust as needed).

I connected Scan94/95 and started the engine. I watched the IAC counts, and the TPS volts. I backed the screw out a 1/4, and then 1/2 turn to see if there would be any value change. None. So I put the stop screw back in 1/2 turn and left it there. IAC was at 10 when the TPS Volts were at 0.63 The target idle was 650, and the actual idle was 638 to 664.

Checked for vacuum leaks. I found one questionalble connection and corrected it.

I checked the Knock Sensor. The wiring appears to be in great shape as does the connector. None of it is anywhere close to exhaust manifold or pipe. I went thru the Search on this website and think I did it correct. I pulled the harness plug off the sensor and got a ohm reading of 3.91k from the sensor to engine block. With Key On, Engine Off, I got 4.89 volts from the harness plug connector end to the engine block. I wiggled the connector around while testing to see if there was any fluctuation.

So it appears that it might have been the exhaust rattling that might have been the culprit like you suggested as well as possible vacuum leak.

I have 2 questions more if you can put up with me for a little bit more. I see that sometimes the IAC goes lower than the Minimum IAC position, is that a problem ? The other question is when I was running the Scan94/95 doing the IAC and TPS adjustments, I turned the Electrical Faults catagory section ON also. When I checked it, it showed Performance Lamp Open. What is that all about ?

GaryDoug

Do you have the traction control/performance switch set in the center console? If not, it's just telling you the lamp is not there.

gaedbo

Yes, I have ASR Acceleration Slip Regulation. Supposedly it is supposed to be on because I didn't turn it off, but for whatever reason according to the Scan 94/95 Software it is not functional whether I have it turned On or Off. Maybe one of the people that owned the car before me had it programmed out, I don't know. If that's what the Performance Lamp Open message is referring to I'm OK with that because I don't think I would ever have a need for it. Thanks for the info.

Injuneer

Wondering if "performance lamp" refers to the transmission performance button, not ASR. Only the Formula/Trans Am came with that button. Wasn't used on the Z28. But I believe the system could be activated in the Z28 PCM, and the button added.

gaedbo

Injuneer, When reviewing the Scan94/95 I see that sometimes the IAC goes lower than the Minimum IAC position, is that a problem ?

Injuneer

The only time a low IAC position is a problem is if it hits "0" and the idle is still above the programmed target value. I don't know if what is shown as the minimum in the data log is the same as the "learned" IAC position. I think that's just a guide to tell the PCM where to park the IAC on shutdown, so it will provide air for startup.

gaedbo

Thanks Fred and Gary for all your input, much appreciated.