dhirocz

So I have managed to get my Z running pretty good I must say. I'm rather happy with the power it's currently making. But it idles like crap.

The car has H/C/I/E to include dynatech LT headers and a small yet unknown cam. Those headers have the tendency to let the 02's run to cool at idle and they stop switching. I caught them forcing the car to go full rich due to a false lean condition. I put in Denso 02's to replace my AFS75's, which helped a tad but did not fix the problem and caused codes on both banks for 02 sensor response (which I turned off with HP tuners).

I also noticed the car tends to stall much more often coming back to idle with the A/C on. It's also a noticbly peppier with the A/C off. The vents also have an issue with airflow...it starts out pretty decent, then slowly goes away as the A/C is on. I vacuum tested the system and fixed a couple of issues already. When I turn the A/C off after it finds an idle...RPM's jump 4-500 RPM before it settles back down.

What I think is going on is a combination of smaller issues leading up to an unstable idle. Fuel is right. Timing is right. Car runs fine otherwise. Sometimes is comes down to idle just fine, sometimes it comes down several hundred RPM too low and recovers, sometimes it flat out stalls.

I do have rolling idle enabled.
I have throttle cracker disabled. It wanted to keep causing a hanging idle at clutch in when enabled, even after cutting 1/2 to 3/4 from the TC airflow table.
Stall saver is on.

What I'm thinking here is that the A/C compressor might be dragging a bit much, the 02's in those particular headers are being lazy at idle, and the airflow from the dash might be the result of a slow vacuum leak I have yet to find with my mighty vac. All these things together cause an unstable idle that contributes to a stall.

I turned PE on down to idle to help stabilize the idle today. A/C on it was 10% rich. A/C off it was 20% lean, both at an idle.

Is there any way I can see how much power the A/C compressor is taking from the engine with the scanner so I can properly populate the tables in HPT? Is there a proper spec for what the compressor requires to operate?

While I'm at it, I see there is a PID for '02 sensor time to activity'. Is there any way to use them to make corrections to closed loop idle fueling? I have tried playing with those tables, but HPT is rather vague, and there isn't really much out there for this beyond 'play with it and see what happens'.

...when my 427 is ready, I'm going to replace them with some jet hot coated Kooks. Hopefully that and the extra cubes minimizes or eliminates the problem with the 02's running cold.

The only other thing I can think to do is to TIG a bung further up into the primary tubes, which I'd really rather avoid if at all possible.

dhirocz

Replying just to document in case someone else has similar problems, since nobody has responded and I've had some time to play with it.

Idles fine when MAF tuning, which makes sense since it's ignoring the 02's at idle. Runs GREAT everywhere else.

minimum PW was too high. It was causing the idle to skew sometimes to the rich side by about 15%, which wasn't helping. It was idling at 2.3ms with a 42# injector. Idle speed was also a bit low for what it wanted, it seemed to like raising it to 950 RPM from 800.

A/C is freezing up, not a vacuum issue. I will pull the orfice tube in the next week or so, flush and refill, and maybe replace the compressor depending on what I find.

I will be using some coated Kooks next time I pull the headers out, to help keep some more heat in. For now, I will be shaving the 02 bungs and switching my denso's to vette rear 02's.

aaronc7

You'll get a lot more responses on the HPtuners forums Gen 3 section. It also really helps to post the tune file and logs capturing said issues if you want the best advice versus random ideas/guessing.

good find on the min pw. i had the opposite issue when i was dialing in the car with 80lb injectors. the supplied min pw data was too low and the injectors wouldn't actually fully open or whatever and it ran really lean. Had to bump it up a hair to avoid super low pw.

tblu92

I don't use HP but EFILIVE --Even though HP has different table name to describe their tuning parameter --I'm sure you can sort out issues concerning your idle/AC load and 02 voltages
1 Desired airflow tables P/N and In gear --should add about 20% to both
Also the Base timing in P/N and In gear and the Hi/low octane tables need to have timing added in the idle fueling tables up to about 20 grams Depending on the size of the cam --Even a mild cam needs more timing something like 23* --The larger the duration add a few extra to a max of about 26*
2. To keep the engine from dying when turning on the A/C add about 15% to the A/C ramp in airflow
3 LT headers are illegal in most states because the front 02's are moved back as much as 3 FT causing them Not to heat up correctly and read HIGH There is NO 100% fix But you can LOWER the front 02 voltage Averages ( that make the fueling Rich at P/T) by LOWERING the front 02 SWITCHING POINTS The Stock switching points are typically 450 Millivolts Try lowering the complete tables to something like 375--This is a trial and error thing
Your average 02 voltages are now probably like 650-700 Millivolts ---Try to get them in the range between .400 to .550 and that should clean the 02's up
4 Try to get your LTFT trims to read slightly negative or "0" Data log them using the MAF HZ data and make precise corrections only in the HZ ranges that are needed to get proper LTFT's