iac should have 12v on one side. there is no need to adjust the tps to .98v, that is a myth. Do you have a tune? you could try doing a base idle reset. Since the TB isnt stock any more, you may have the TB open too far.

 

"no need to adjust the tps to .98v, that is a myth "
Oh, my F'n God, I can't believe that someone else is sharing this!
I've been saying this for years while Brew and others are like "You gotta set the TPS...!!!"
Uh, no, you can even see the ECU use the current TPS WOT setting with any tuner dashboard software.

 

Base Idle reset procedure is ONLY for a completely stock engine.
OP has an aftermarket cam, and is trying to achieve an 840 rpm idle instead of the 672 rpm stock idle.

The base idle reset procedure is NOT for setting an idle, it’s for returning it back to stock, on a stock engine.

It won’t work here for this purpose.

If unplugging the IAC valve does nothing while it’s running, then it’s maxed closed. It should be about 35% open at idle.

Disconnect your IAC and Plug in one of your spares while the engine is running and see what happens while looking into the holes. Does it move, or max out.

smoke test again.
check throttle body blade to ensure it is not sticking/ hanging open.

 

Base Idle reset procedure is ONLY for a completely stock engine.
OP has an aftermarket cam, and is trying to achieve an 840 rpm idle instead of the 672 rpm stock idle.

The base idle reset procedure is NOT for setting an idle, it’s for returning it back to stock, on a stock engine.

It won’t work here for this purpose.

If unplugging the IAC valve does nothing while it’s running, then it’s maxed closed. It should be about 35% open at idle.

Disconnect your IAC and Plug in one of your spares while the engine is running and see what happens while looking into the holes. Does it move, or max out.

smoke test again.
check throttle body blade to ensure it is not sticking/ hanging open.

Base idle reset works regardless if its stock or not. Ive used it on more cars than I can count that were not stock or even close to stock. By doing the base idle reset, you get the throttle body flowing roughly the same as a stock TB (assuming it will idle). IF the air mass going through the TB is significantly higher or lower than what it set at in the tune, the engine will surge. Here is why it works. When you unplug the spout, tps and IAC, the only thing controlling engine rpm is base timing and the air passing through the TB. If you set the car to idle at ~600rpm with all of those disconnected, it doesnt matter if the car has a 100mm tb or a 5mm tb... The airmass to get the engine to idle at 600rpm is the same. If the car needs a tune, its not going to fix but if the airmass is significantly off, it may correct the issue. Lets also not forget that the base voltage from the TPS was 1.1v.. That also points to the TB being open too far...

 

That base air mass flowing through the throttle body with IAC, TB, & TPS is a scalar setting in the tune , and is very specific.

And if that setting doesn’t match the scalar, the EEC tries to correct it which results in the surge/ stall.

Thats why it’s not intended/ (works) for anything other than a stock engine.

 

ITHBMA is the throttle body airmass with the throttle body closed and IAC at 0% duty cycle. If TB is not flowing the same as what is in the tune it will cause surging (as you said). The default setting is .4895 lbs/min for a 94/95 GT. If the actual TB airmass is significantly off from ECU setting, its going to cause surging regardless if the engine is stock or not. Its going to cost OP nothing to try a base idle reset... At worst, 10 minutes is wasted, at best, the car stops surging. He will still need a tune to take full advantage of all of his mods regardless of the outcome.

 

He has already done it, a few times, and it didn’t fix his issue.
Likely made it worse, then he blindly turned the airbleed as well.

And who knows if the previous tuner addressed it or not, so one cannot recommend that procedure for a modified engine.

I doubt seriously that had anything to do with the problem in the first place.

It’s more likely to be a vacuum leak or sticking throttle blade.

But let’s wait to see how the spare IAC valve behaves when hooked up.

 

If your able to stabilize into an idle manipulating the gas pedal, then ITHBMA likely within range (typically I find it's more critical for tip-in/light cruise) as well as all your sensors are fine (KOER will confirm if your sensors are good). If it always ends up stalling, then yes, it's a s/w tune or sensor issue.

-hunting/surging idle < 60 secs at startup, cold or hot: startup enrichment tables
-otherwise, most of the time when I got idle hunting issues, it was actually the distributor aka bad stator (recall CBAZA uses spark to control idle rpm) or leaking PCV/VC leaking or vac leak.

 

was testing earlier today, and started to surge when warmed up.

Disconnected plug on IAC while running and the car wanted to stall out, so had to turn throttle screw up some to maintain idle. Connected spare IAC to plug, it was barely moving. Tested voltage again and it was only 4.5v'ish but would vary with the throttle

Disconnected the IAC plug, car would bounce between 800-1000, disconnected the spout, rpms dropped a little but continued to surge with both items disconnected.

 

First off, the voltage to the IAC is not constant, it’s a pulsed duty cycle.

it should not surge with the IAC & SPOUT disconnected, as you have removed the EEC’s ability to control idle.


do you have a fuel pressure gauge and a vacuum gauge? Your issue might be mechanical.

although I do suppose it could still be a leaking capacitor in the EEC, they do weird things when failing.

 

First off, the voltage to the IAC is not constant, it’s a pulsed duty cycle.

The negative side is pulsed. The positive side of the iac has constant 12+

 

sorry for the delay. I worked on it this morning then had to scramble to my niece's band concert.

So, the variable IAC voltage makes sense then. Today I did a second smoke test and sprayed around all the vac ports, nothing. Just for grins, I replaced the upper intake gasket (had a spare), no change. Checked my PCV, its sealing up and drawing nice amount of vacuum.

Here's the collection of videos from this morning. Again the idle is bouncing from 800-1000rpm

Vacuum at idle
IAC spare testing on harness
TPS voltage


Also these videos were taken while the spout and IAC were disconnected. I also checkd my base timing and it is at 10deg, so the balancer didn't slip or anything like that. As mentioned, this all started when the TPS Signal wire & Ground wire accidently connected which has me believing something electrical, for lack of a better work, gone kaboom

 

Today I did a second smoke test and sprayed around all the vac ports, nothing

This is not the right way to perform a smoke test. Needs to smoked from the inside of the upper intake at the throttle body or mass air meter building up a minimum of 4psi of smoke pressure.

 

If you hold the throttle steady, at say 900 rpm, does the vacuum gauge fluctuate?

 

If there wasn't smoke coming out of area's like the dipstick tube like it should then I would be skeptical that the test wasn't being performed properly. And unless a person has performed the smoke test successfully a dozen times or more probably not being done correctly. Just my opinion. Lots of trial and error to get it right with conclusive results.

 

Oh no doubt, and this was my first time trying that test so I'm working with very limited experience.

Everything I'm witnessing tells me it looks like a vacuum leak, but having a hard time believing it since nothing other than a tps/iac were removed. Not saying it isn't, just that all the vac stuff I went through less than 5yrs ago, and its been rock solid since. But when the tps was electrically shorted while running is when it really started.

Going to pull the ecm tomorrow to inspect for anything obvious

 

So interesting development,

Took the computer out, no obvious signs of burnt resistors or even a electrical smell. But erroring on the side of caution I took the chip out. Also got to thinking since this seemed heat related, I decided to put the original O2 sensors back in, figured what the hell, try it out. Started the car and it started nice & perfect, idle sitting about 800 on factory tune. After getting it up to operating temp, I shut it off and restarted it 10min later. Still idling perfect, no surge

I decided to run codes just to be safe got the following

• 1st test - got a 543 but was immediately interrupted on the first result. Just as soon as the 3rd flash occurred, it acted like something lost ground and I could hear the fuel pump energize again and then nothing.
• 2nd test - Trying to make sure my test write wasn't loose, this round I got a 542 instead. Test completed successfully and flashed the code twice
• 3rd test - Got to the same 542 this time, but like the 1st test, it cut out and energized the pump again, test was over

Unsure if the issue was the aluminized piece of wire I was using in the self-test port, I decided to try copper instead. next two tests were same, same 542 each time. So has me thinking maybe the test wire i was using wasn't too reliable to begin with and the 543 might of been erroneous. For grins, I decided to put the stock ccrm back in, cleared codes and restarted.

Car fired up, making good fuel pressure at rail, but idle surge came back for first 10sec and evened out. I let it run for about 10min and attempted to back it out of the garage, it stumbled pretty bad on power. No CEL, but it was having a hard time backing up or when I pulled it back in garage. Ran codes again, still got a 542.

So, (542 - Fuel pump circuit failure), with two ccrms same result. The pump was new last fall, its a Walbro 190. It energizes each time I turn the ignition on. Car has no problems starting or making pressure. Its apparently stumbling, Idk, maybe a bad ground or loose? I'm not even sure where to start on that

 

The fuel pump is clearly energizing, could the 542 be misleading since I changed the O2s?

 

What is the fuel pressure?

 

Does the fuel pump stay on constantly or does it turn off after a few seconds after the key is turned to run without starting the car?

 

Best I can tell it energizes for a few secs like it should, and the car starts without issue. While idling I'm at 35psi, but when it surges I can see the pressure dropping around mid 20s and then shoots back up. I think tomorrow I'll put a meter on the harness in the trunk to see if I can verify voltage drop to the pump when it surges

 

Just turn the key to the run position, dont start the car... Does the pump stop pumping or does it continue to pump any time the key is in the run position?

 

When I turn to ign the pump energizes/primes a few secs, then quiet. Have steady pressure at the rail. But to be honrst I haven't let the car sit KOEO long enough to hear if the pump tires again. I'll try it out in the morning

 

Just double check the pump is turning off. You don't need to make sure it doesn't turn on again by waiting. If it turns off after a few seconds it's working as it should.

 

Sounds like bad capacitors could be an issue (only one ECU is doing this right?) I've read that fuel problems are the usual symptoms...

 

Go figure, tried 3 times tonight and test completed successfully each time. 542 every run. Making me think the first piece of wire I was using was janky to start with.

Tomorrow I'm going to switch the other o2s back in and see if anything changes

 

You already know that the fuel pressure is dropping.
Your next step should be monitoring the voltage at the fuel pump when this happens.

If you lose voltage, the problem is upstream from the pump. (CCRM, EEC, wiring)

If you don’t lose voltage, then the problem is in the tank (pump, lines, regulator)

 

Agreed, that's my plan today is to measure the voltage at the pump and see what happens. Lucky for me I work from home, but still tough to get time to go do that. Gonna try it later tonight

 

Got a break today to test. To check voltage I used the harness in the trunk going to the pump, ground to chassis.

While the car was cold, idle sat perfect at 800-900rpm, and voltage was sitting pretty at 13.5v
As the car was warming up, the voltage was down to 13.3v, but holding steady
After the car got to operating temp, the surge returned, 800-1100rpm and the voltage was fluctuating between 13.3v and 12.4v
Fuel Pump Voltage 1
Fuel Pump Voltage 2

Observation of fuel pressure & rpms
Fuel Pump PSI
Idle Fluctuating

Just a note, I did swap out my O2s back to my newer NTKs, still getting the 542 code

 

Think we can eliminate the ccrm since I used two, original + a 2mo old aftermarket

 

Alright, maybe I missed this... But...

Clearly idle spark and IAC are doing different things, they work together.

Have you tried this simple thing?

Mark current position of idle stop screw.
Start it, unhook the IAC, turn the idle stop screw in (clockwise) 1/2 turn. Continue until surging stops. Back off 1/2 turn. Plug IAC back in.
Turn off car, start it and see if that handled it.

TPS sets zero every time you key on.

Another option is to install an IAC bypass plate. I used one back when I had an E-cam and it worked fantastic.

Got to remember, if the car isn't tuned to a new higher idle RPM the idle spark and IAC will constantly fight against you to bring the idle down (By lowering IAC duty and dropping ignition timing) If the cam isn't much bigger than stock I'd try to get it to idle at or just a hair above stock.

 

Actually yes I have. I can get it to surge with & without the IAC, or even with the spout dissconnected. No matter what combo ive tried the car surges anywhere under 1500.

The pump should be getting constant voltage and clearly it isn't. That has to be figured out regardless of the throttle stop screw/IAC combo. When I shorted the leads on the tps, is when this all began. So i clobbered a wire or a capacitor in ecu is hosed. Whatever it is, its definitely is heat related, cold car, idles perfect, warms up it gets possessed