It's really too bad that EEHack doesn't work on the '96--I wonder if GDScan will let you look at the actual IAC counts? There are lots of data values that are useful for diagnosing issues like that.

If you haven't checked it out, check out GDScan to see if it can help you: https://www.mediafire.com/?0elo4c935uc5s

 

They removed the upstream O2 sensors? That would put it in a permanent open loop. Why?

 

I think he means the post-cat sensors.

 

I have the SnapOn Modius scanner I borrowed from a friend. I can read data while the car is running. I can clear codes. I cant tune it though. My IAC memory always says 32 counts. It has always said 32 counts even with the new PCM and the old PCM it says 32 counts. This makes me wonder if the circuit is messed up. With the old IAC it ran 2000 rpms at idle. The car does run in closed loop on the scanner so there is no problem there I guess. Even though he turned some stuff off in my PCM everything is still connected as if it were stock. I have no codes at this time.

It was cold and super windy today and I didn't get a chance to mess with it much today. I did get the TPS set a .65 volts. Keith told me .67 is the best spot but mine wont turn anymore to get there. I will have to physically adjust the idle screw to get it to .67.

I didn't get a chance to hook up the vacuum gauge. The KPa on the MAP is in 50 to100 at 1000 rpms, foot barely resting on the pedal to hold it there. Or it just dies. Has to be a vacuum leak. I verified the small tubes that go to the HVAC controls and the vacuum cannister hold. I can put 10hg on them and they sit there. I know the booster is working as the brakes are good. Would the vacuum lines to the Opti cause and issue if they are leaking? It just pulls clean air through the Opti from the air intake. There are two valves on that line and as far as I know that line is original and looking pretty old. I just dont know where else to look.... This is madness. Once the idle is fixed its a good running and driving rig. I can get back to blowing more money on shocks etc...

 

I normally set timing for 6 and set the IAC to 20 to 30 counts when the engine is in closed loop and then set the TPS if there is an adjustment

 

'90 and up TPS are self-zero'ing. There is no adjustment, you're just using normal slop in the screw holes.

The idle screw in the throttle body is for the minimum idle air setting and affects the IAC counts. When you rev the engine, do you see the IAC counts change? In the '96 Service Manual there is a procedure for setting the IAC. It's been too many years so I don't recall the specifics, but it is in the manual.

 

This. The only adjustment relating to TPS is adjusting the physical throttle cable to make sure you get the full 0%~100% TPS range accoridng to the PCM, and recalibrating the ABS computer (which currently requires a Tech 2 to do). There is no adjustment on the TPS itself. Similarly I don't believe you're supposed to be physically adjusting the idle itself. It sounds like the Snap-On may be polling the incorrect PID and thinking it's the IAC counts. I'm not familiar with that tool so I cannot say for sure, my apologies.

 

I don't know about other situations but if you make changes, I think it is possible that you have to adjust the IAC.

I don't know but my Snap On brick does seem to poll the data right on my 91. I have doubts that the tool they make for the mechanic is that bad. It may be but I'd bet against it being wrong.

 

I have had a LT1 induction on my L98 engine, with HEI in back up top, and a 1227730 speed density computer for a long time....and was having issues from time to time over recent years......I finally figgered out that 24 lbs injectors were right, AND I was running only ~30 lbs pressure.....RONG I finally got a longer screw on the FPR and jacked it up to the 43.5 psi it was supposed to have.....reset the idle, with IAC at ~27 something....

and its been fine since.....running LO fuel pressure caused the computer to dump fuel and screw up the idle like MAD sometimes I would have to run outta the garage......lo fuel and the puter tells injectors to just **** fuel like MAD, and I was told that is a fuel stream, and not sprayed in a fine mist.....

made a bit of sense in my shituation.....and car runs fine now.....

 

The snapon tool doesnt show you actual IAC counts while running. That's a bummer but it might be that way as the IAC for this car is not adjustable. It only shows IAC memory and mine says 32. It says 32 on this new PCM and on my original PCM, weird. There is a way to test the IAC where you can run functional test and tell it to move the idle up and down and it does seem to make changes when you do that. The IAC is not adjustable on this car.

I did get to work on the car today. My friend who owns the tool came by and we went over the car some. Tried a few things and it wouldn't idle. Then he had me remove the IAC and the pintle was fully extended, 1 3/8". He had me leave it out and start the car and he blocked the hole and meter the air with his finger. Doing that it would easily idle at 700 rpms or higher. He ever so gently pushed the pintle back in like the manual says. I reset the IAC per the manual directions and it would idle at 850. It sat there and idled for a good 10 minutes. We wanted to see if it would eventually stumble and die. It didn't. I took it for a drive around the neighborhood and it worked good. Hit several stops and it never died. It's alot easier to drive a standard when it is not revving 2000 rpms with the clutch in... But the idle felt weak like it wanted to die. An hour later or so I needed to move the car and it wouldnt idle again. It would try but wouldn't hold. For some reason the IAC is shutting off the air.

While my friend was over we went over the other items on the data. The fuel mixes at idle are now very close to 0 as they should be with the tune for this cam and the proper injectors. This tells me that it is not seeing a bunch of unmetered air like it would if it had a big vacuum leak. But the issue that is causing the weak idle appears to be the MAP (KPa) is 56 this translates to only 8psi of vacuum. This cam is not that big so it should have plenty of vacuum. The duration at .50 is 218 228 so it should still pull vacuum in 14 range at idle. 14 would give it a very strong solid idle. More testing is needed.....

Something is driving the IAC shut and the engine wont pull vacuum....

The engine is very new with only a couple of hours on it tops. I am thinking some time on it out on the road, 50-100 miles on one run, might bring it on in. Every time I drive it around the neighborhood, and aggravate my neighbors, it seems to run better. It runs at temp 195-200 on the digital gauge and the analog matches that number as well that's huge plus. But it's not tagged and inspected right now so its ticket machine just waiting to be caught...the saga continues...

I do want to thank you all for all of your ideas and help on this...PLEASE KEEP IT COMING!

 

No clue about an LT4 but I would feel that if you have a throttle body with a screw, you can adjust the minimum air rate. You can't change the idle. That is an ECM commanded thing.