Surging idle on cold start

[thinger2]

Hello everyone, my first post! '94 5.7 TBI with 145,000. Truck is original and last year developed a miss/bad idle in gear. I replaced the IAC, TPS and EGR, plugs, wires, cap, rotor, still had the problem. Checked the fuel pressure, good, 13 psi. No codes. Next, I noticed that the distributor was making noise, bad bearings. Replaced the distributor and problem solved, the truck was running great! All parts replaced were Napa/Echlin. Now the temperature is dropping, and on cold morning idle surges badly for about two minutes, then smoothes out and runs like normal. I have tested the coolant temp sensor and it checks out, and still no codes.

This seems to be a common problem that has been discussed on many forums, but I cannot find a forum with a resolution or an answer!
Any help would be greatly appreciated-

Kevin Showalter

Ive looked through the same forums with no answer.
Im starting to suspect that our problem is the end result that may be caused by different issues for each of us.
Not by one thing, but the end result is a cold misfire.
Something below a certain air temp is making it try to start way fat or lean and causing a cold misfire.
But its friggen odd.
Mine starts puking at about 45 degrees
And then its done.
Runs fine for the rest of the day.
Somewhere, either in some strange afermarket part, or a ground, or an aftermarket sensor.
Something is a bit off.
And the gm dummy box cant handle it.
Solve this and I will ship you a case of beer of your choice my friend.
Its a common problem with no answer.
Yet

 

[thinger2]

What I should do is get the live data and figure it out.
What Im goung do is slowly warm up the sensors with a heat gun and see if it has the same problem at startup

 

[Schurkey]

No problem above a certain air temp.

For sure temperature related.

As soon as the ice water and 50 mile an hour winds stop.
Its been a ratty month in the PNW

the end result is a cold misfire.
Something below a certain air temp is making it try to start way fat or lean and causing a cold misfire.

Mine starts puking at about 45 degrees

Rainy, 45 degrees, runs shiitty, maybe stalls?

Does the flapper on the air cleaner snorkel actually work? Draws heated air from the heat stove around the passenger exhaust manifold, through the expando-tube, into the air cleaner?

'Cause this sounds a lot like throttle blade icing to me.

 

[Schurkey]

Now the temperature is dropping, and on cold morning idle surges badly for about two minutes, then smoothes out and runs like normal.

Does the IAC work properly? Have you ever cleaned the IAC air passage using aerosol carb spray or throttle-body cleaner?

I have tested the coolant temp sensor and it checks out, and still no codes.

HOW did you test the CTS?

I did not install a new ignition coil.

Probably just as well. "New" coils are often not as good as the original that's being replaced.

TEST before replacing.

 

[K-Man]

Testing the CTS. 5 volts at the connector, and then take ohm readings on the sensor itself. It is something like 3400 ohms at 70 degrees fahrenheit coolant temp, then at running temp of say 190, ohms read 260. Google GM temp sensor chart.

 

[K-Man]

Ive looked through the same forums with no answer.
Im starting to suspect that our problem is the end result that may be caused by different issues for each of us.
Not by one thing, but the end result is a cold misfire.
Something below a certain air temp is making it try to start way fat or lean and causing a cold misfire.
But its friggen odd.
Mine starts puking at about 45 degrees
And then its done.
Runs fine for the rest of the day.
Somewhere, either in some strange afermarket part, or a ground, or an aftermarket sensor.
Something is a bit off.
And the gm dummy box cant handle it.
Solve this and I will ship you a case of beer of your choice my friend.
Its a common problem with no answer.
Yet

I'm beginning to think you are correct, and it is annoying throwing parts at it. The good thing is that the damn truck runs, every time!

 

[PlayingWithTBI]

This is OBD1 data stream? What software did you use for this?

This is TunerPro RT (freeware but a suggested contribution) and an ALDL/USB cable on my laptop.

curious how this would point to ICM, Ignition coil issue?

The ICM gets hot (maybe not properly installed with thermal paste), then throws intermittent pulses which the ECM thinks is higher RPMs so it adjusts accordingly to the cells in VE and SA tables. In this case it was an almost brand new Spectra Premium distributor and a Pertronix Flame Thrower coil. After installing an ACDelco D1984A ICM, it ran fine but still had a little surge at idle. I sprayed some water on the coil and it almost died. You can see the arc burning between the body and the iron.

You must be registered for see images attach

Replaced the coil and all is good. YMMV

 

[K-Man]

Is there a proper way to calibrate the IAC when installing new? I remember seeing a video about removing battery terminals and shorting hot and ground wires for a few minutes to drain any capacitance in the ECM which resets all parameters? Does that sound right?

 

[Sabinoerc]

I finally invested the time to set up datalogging after chasing stuff like this on my 93 5.7. TunerPro is good and is what Playwtbi used for screenshot he showed.

I had surging problem at cold start once which turned out to be marginal fuel pressure. Fuel pressure was 11psi. On cold start I guess that wasn’t enough for the default A/F map when open loop on the old engine. I only figured it out by watching datastream an noting that “idle enrichment” (or something like that, can’t remember) was kicking in when it surged. Replaced fuel pump (13 psi) and problem went away as well as a late shifting problem I was thinking was just a tranny problem.

You might try to narrow down if your problem is just during open loop or also during closed loop. memory is you can short pins on the ALDL connector to show if it’s in closed loop. Google should be able to check my memory.
I think, but don’t know, more a guess, that when in closed loop there is more trim adjustment capability by ecm which can mask problems with fuel, air leaks? So perhaps something which you don’t notice in normal closed loop operation is noticeable in open loop. That was my case. Regardless, many people with much more knowledge in this area than myself on these forums maybe other ideas will pop up. Good luck!

 

[PlayingWithTBI]

I changed my ECU about a year ago to repair my code 82 issue. That’s when it first started

When you changed it did you use the same chip from your old one? Maybe your "Choke" tables are different?