95z_28_camaro_4_Ivan

So my car develop this new problem, the car starts just fine and drives just fine for like the first 2 or 3 minutes, but when the car reaches operating temperature, and I come to a stop or red light, the idle quickly drops from 800 to 500, 300 and then it stalls.

Car starts right up, without hesitation, however it will continue to stall, unless i give it gas when i come to a stop sign or red light. But once I get going, the car drives without any problems. The problem only shows up when I decelerate and come to a stop. Car just loses idle RPM and stalls.

Prior to this problem, I changed the fuel pump.
After this problem, I changed the fuel pressure regulator and the IAC. The problem still showed up after those 2 part replacements.

I checked the fuel pressure and this is what I got;

Priming 35
Running 32
running w/ vacuum disconnected 40.


I scanned it, no codes... Here is a scan file I recorded from scan9495,,...
https://www.dropbox.com/s/xjmsjsnkbk...36941.csv?dl=0

if you guys can point me in the right direction please.... thanks in advance...

shoebox

Did you reset the IAC after replacement? Gotta do this so the computer can sync position.

Injuneer

One problem with the log is that it is only recording at about 2.5 frames per second. A faster scan would probably allow more detailed analysis.

The IAC counts are very high (87 - 89) trying to keep it at 800 RPM at idle.

At higher RPM driving, the counts go up (as they should) as high as 114. It does that to prevent stalling when the throttle blades suddenly close. When the throttle goes closed to decel, and the speed starts to drop, the IAC commanded counts drop like a rock, into the high 50's and low 60's. Based on the high count required to hold it at idle, it obvious its going to stall. The PCM does not raise the IAC counts to make up for the engine RPM dropping below 800 RPM, so it stalls for lack of air.

I looked as decel fuel cutoff, and the PCM brings the injectors back on at a fairly high RPM, so it's not lack of fuel. Strangely, the injector pulse widths start to climb after the fuel cuts back in, even though air flow is dropping. It's dumping in a lot of fuel, and there isn't any air. Then, just as it's about to stall, there is a big dose of knock retard. This is the result of MAP rising quickly, right up to barometric pressure, which it should not be doing with a closed throttle.

Repeats the same pattern all three times it stalls in the data log.

I have never seen anything like this before.

Fuel pressure may be a bit low...

Should be 43.5psi at idle, with vacuum line disconnected. GM accepts anything in the range of 41-47psi, so you are outside the lower limit.

95z_28_camaro_4_Ivan

I did the reset method a few days ago and didn't make a dif... Unless I'm doing it wrong...

Car off, hit the accelerator for 5 Sec turn car on release accel let it run for 10 Sec and shut it off....

Still stall on me...

I remember it started doing this after I got the aluminum elbow that connects to the throttle body, because the stock one tore.... I don't supposed this has anything to do with it right...????

Injuneer

How big is the cam? Some 58mm TB's are known for poor idle, often requiring holes to be drilled and tubes to be inserted. Descreened MAF is always a problem.

But if it ran OK before with these mods, no reason it should change suddenly.

I can't see why the aluminum elbow would affect anything.

.

shoebox

That isn't exactly what the link I posted says...

GaryDoug

It looks like you have an ignition voltage problem. It never gets far above 12.5v when running. When stalled, it immediately drops to about 11 volts (low speed fan is on all the time due to a/c), sometimes as low as 8-9 volts for one scan period. That's when you see some very brief, strange and impossible scan readings, like 253 mph, 25 vdc for ignition, phantom DTC's, etc. Sometimes the scan program recognizes the bad data and recycles the connection (3-4 seconds time). I would run another scan with the a/c off. Great a/c performance, by the way;-)

95z_28_camaro_4_Ivan

I'm not sure how big the cam is... I got it years ago and I never really had a problem with it nor with the 58mm throttle. I can try to dig up some old emails with the size if you think it might be relevant...

I might do the AIC reset again, since I think I might have screwed that up...

I'll do another scam and post it, hopefully it can be a more detail scan....
I don't know why it's scanning every 2.5 seconds though... I'll try again...


It's a brand new AC compressor by the way...! Lol

GaryDoug

Some tips for making a faster scan:

1. Disable all scan sections except Engine (only Engine should be green)

2. Do not enable "Auto-save scan file" on the engine tab. Instead, wait until the end of the scan to save the data to the log file: Click on the "Save Scan to Log File" button. Don't forget to save it at the end, or the data will be lost.

3. Make sure the "Wait (ms)" value is set to 0

4. Leave the display showing an inactive tab, like Transmission, Elect Faults, or ABS. That way the app won't waste time updating the display. Don't show the graph tab, that is the slowest.

95z_28_camaro_4_Ivan

Will do Gary, thanks for the tips... Will update soon!

95z_28_camaro_4_Ivan

Ok so, I re-set the IAC per shobox instructions, so I know I did it right this time... I took the car out for a drive with the AC off, and the car did not stall once.... go figure?? however when I turned on the AC, the idle drops and the car stalls....

This is the detail log with the AC off...
https://www.dropbox.com/s/egoe4mmlhh...36941.csv?dl=0



This is the log when the AC is turn on the the idle drops until the car stalls...

https://www.dropbox.com/s/wgqr5hasaa...36941.csv?dl=0


It is a new AC compressor that I had installed recently by a local mechanic...


The car also started knocking really loudly, definitely something sounds not right... I took a short video with the valve covers removed, I was hoping that it would be something obvious on the top end, but I didn't see anything...

Here is the link to the video...
https://www.dropbox.com/sc/nfnv3dm50...3LwEliwP02pIKa

GaryDoug

In the first scan, the IAC seems to be working during the warm up period. It drops the engine idle speed as it warms up. It does seem to operate on the high side of it's range though. In the second scan, the pcm is attempting to raise the idle speed slightly at first, but the IAC valve is already maxed out and can't go higher. Since the difference in the target idle speed and the actual idle speed is small, it probably isn't noticeable. Then when the a/c is switch on, the rpm drops and the IAC can't go any higher since it is at max value already. Now why it is still doing that I can't say since you replaced the IAC valve.

shoebox

That engine sounds like it has internal problems. The squeak and low knocking (not the tapping sound) sounds like a rod bearing.

95z_28_camaro_4_Ivan

I was afraid it would be something like that... I searched a few vids on YouTube under spun rod bearing, and it's a really familiar sound. ��
Well, I may just have to prioritize my 396 Eng upgrade... I've been saving for all forged internals...$. A friend suggested I just get an Ls engine and call it a day... Any thoughts on that????