Think I found the air hole for the IAC, it’s on the inside of the TB (see pict)

So blocking it to see if the engine stalls or stops would mean running the engine without the elbow/MAF connected

Some say that the engine should stop when you disconnect the MAF, if it works properly, in my case it didn’t do that …..

Had it off yesterday and it can definitely do with a cleaning, also my Elbow rubber is really torn in the end towards the TB although the clamp likely is keeping together when tightened

I’mgone start with cleaning up the MAF with some proper cleaning spray

 

I have never seen a car that shut off if the MAF harness was pulled.

How a MAF sensor work. The map sensor heats a small wire to say 90 degs (this can vary per manufacture) above the ambient temps the system then needs to figure out how much power it takes to keep the wire at that exact temp. As the air flow increases the amount of power it need increases so the PCM know how much air is entering the engine by how much power is needed to heat that wire. To do this accurately the PCM needs to know air temp and barometric pressure before it can do the correct calculation. When you start the car it is almost instant. It does not have accurate information form the sensors yet. The car starts in open loop mode. This will ignore almost all sensor data and it will run. It will be a little rich and it will not advance the timing much. (think of it as low power mode) this way nothing gets hurt. Once the system gets into closed loop all the sensor data is taken in and used for fine adjustment. If your MAF senor was sending info that did not match up within the limits the factory set it does not guess what is wrong it just goes back into open loop once again ignoring most sensors. That is why the test of unplugging the MAF sensor does not automatically mean the MAF sensor is bad. Lets say the BAP sensor is reading wrong you unplug the MAF sensor that puts the car in open loop and the car runs better because it is ignoring the bad BAP data. You may think that would set a code but a sensor can cause issues with the way a car runs and not set a code. Again the BAP sensor real thinks you are in Denver and you are at the beach. There is no way the PCM can know you are not in Denver other then pressure. I use the BAP sensor as my example because it is the least likely sensor to be bad. I have found most people skim through long long explanations like this and will come back "you said my BAP sensor was bad".

I always thought if I ever taught a class I would call open loop "carburetor mode". Only because it works more like a carburetor without any feed back sensors then like you think EFI works. Course now a days most kids have no clue what that would mean Whats a Carb-er-a-tor

Again the MAF sensor is fine adjustment. Back in the 80's most of the MAF sensor failed under warranty. It was so bad GM stopped replacing them. The sent out new programs that just ignored the MAF sensor data and would not set a code. The fuel/ignition mapping relied on the air temp and the MAP sensor to fine tune the car. I only say that to point out the MAF sensor data is not critical for the car to run.

Could a manufacture tell the PCM to shut the car off if it sees a lose of the MAF signal? absolute. It would protect the Cats for contamination BUT due to power steering and power brakes random shut off are considered a safety function. If a manufacture did shut off an engine because of a MAF sensor they may find themselves being investigated by the DOT and on the wrong side of a law suit.

Back in the day GM had bulletins that said Nothing should ever be sprayed on a MAF senor. They where aware of the spray MAF cleaners but said they are more likely to hurt the sensor then to clean it. That was a while ago and if the sensor is causing issues then what is the harm in trying before you replaces it?

Yes I have used the carb cleaner to look for vacuum leaks. You can use pretty much anything that is oil bases even WD40 if that is all you have, It works best on carb cars or EFI in open loop but it will work in any setup just not as dramatically. If you get a chance look up Vacuum leak and Smoke machine on youtube. That is how a pro finds the hard to fine leaks.

Edit: one last thing there should be two holes at the throttle body. Think of it as the throttle plate by pass. Air goes into a hole at IAC from the filter side of the throttle plates and through the IAC and out the engine side of the throttle plate. The exit hole can be farther in toward the engine. I have worked on so many different cars sometimes it is hard to keep straight which is which. Some cars use only the IAC and some cars crack the throttle plates for base idle and use the IAC to fine adjustment. If there is an adjustment screw on the side of the throttle plate then yours it is the latter. Drive by wire cars have none of this stuff but the LT1 was never DBW.

Hopefully giving you the how it works story may trigger something you can see that I can not.

 

I appreciate you taking the time to sort this out for me.

I would probably count as a carb guy as I did my car mechanic education back in 1978-1980, have never worked with cars professionally though, it did become a dear hobby, however.

So for the computer and sensor controlled stuff with layers of different systems that arrived during the 80’s and on, I have only learned about it partially, never got the full picture.

Your description of the MAF is very clarifying, and I now have a lot better understanding of that component.

Regarding engine stopping when disconnecting it, I saw that on a youtube video, not all things you pick up on the net are accurate and vehicles are different.

One clever thing I saw on another video was to block the vacuum lines off (one by one) with a lockable pliers, lets say you have a vacuum leak inside the brake booster and squeeze the hose going there and the stalling stops, it tells you the issue is there.
I may try that later


One thing I have thought of regarding vacuum leaks in my specific case is, shouldn’t it be there all the time? Or could the car hide it by try and compensate for it? And if so why not all the time...
This only me thinking loud, so don’t feel obligated to reply unless you want of course

 

Small update: this weekend I cleaned up the MAF with the appropriate spray, the honeycombed part was dirty while theinside with the three leads looked rather clean.

Also replaced some of the dried out small vacuum hoses on the passenger’s side of the TB, they were not really broken but had several small cracks in them.

Then had the car out for a normal 20 min drive, left it idling on the driveway for 7-8 min, and absolutely NO idling issues, that said I doubt I’m out of the woods yet as it took longer time before the self-reeving occurred last time, and the car had then also been driven harder in a higher ambient temp.

Whatever it is it seems triggered by high temps, both engine temp sensors have been replaced btw

Will do a TB overhaul later on, currently waiting for parts (IAC and TPS) which will arrive later this month.

Regarding monitoring the different engine parameters with my OBD Link MX+ that didn’t work out for me as mentioned earlier in this thread, I discovered that you need to open up several settings in the ap before it works, I didn’t know that as I thought it was preset, so might try that again as it’s a smart way of see what regulating system is active during the self-reeving.

 

I did the ICM mod, that is put some washers behind the coil/ICM bracket to spare the components from the engine heat.
As the problem seems to be heat related, it felt like it could be it, but sadly no improvement..

 

Manged to monitor via my OBDLink dongle & app, and share the result here, engine fully warmed up and idling.
Found nothing to shed any light on the surging issue though, not sure how much live data you can get from a LT1, but a dream scenario would be to be able to see what engine parameters that are lively in there as its seems to be a regulating issue.

Have been thinking on consulting a professional tuner

 

did you check intake manifold bolts for tightness/torque down.

 

No I haven’t, did spray some brake cleaner in that area though, but it’s a good point, I’ll do that tonight, thanks Craby!

 

Got to check half of them last night, and so far they were rather poorly torqued (wrench set to 48 Nm) and one even loose, will do the rest asap
Have a small hope this might be causing the surging.... but we will see, I will report here regardless

 

Was some work to undress the engine to be able to tighten all the intake manifold bolts and studs, but now it’s done (except for #11 under the fuel regulator that was harder to get).

Sadly, it had no effect on the surging, but they should not be loose regardless, so the work was not done in vain.

So need to move on with the troubleshooting.

Parts being replaced so far:
IAC
TPS (but have put the old one back, as the new cheapo was crap)
Both temp sensor (due to dead gauge)
Throttle body gasket
Elbow
Fuel filter

Stuff that has been made:
MAF been cleaned with MAF spray cleaner
ICM mod (washers installed to separate the ICM from the head to spare it from heat)
EGR has been off, checked the diaphragm with a vacuum pump, cleaned the valve section with some brake cleaner, and also cleaned and lubed the diaphragm shaft
Sprayed start gas around the injectors to check for vacuum leaks
Intake manifold bolts, studs and throttle body bolts re-torqued


Stuff that I have been thinking about to do:
Recalibrate the IAC
Pull the vacuum hose off the EGR while surging to see what happens
Somehow probe the IAC so I can measure voltage alternation while surging
Replace ICM and coil
Hire a professional tuner for support with the troubleshooting

As surging can be different from case to case, I've posted a video so you can hear how it sounds

You Tube