Engine Surging idle issues

AnthonyA1234 · May 29, 2022

So a few weeks back in a attempt to solve my surging idle issue I did a smoke test and found that one of my valve covers was cracked and was leaking vacuum. So I took the manifold off and I changed out the valve covers and while I was in there I also put new act and ect sensors. Today I put everything back together and it still has surging idle issues and the car will stall out. It’s weird though it never does this the first time I start the car in a while it’s always when I try and start the car when it’s already at operating temp. I replaced my whole fuel system, fuel pump, tank, injectors, and regulator set to 43 psi with vac line disconnected. The car also has a new distributor, wires, and plugs. I set timing to 14 degrees spout out. The car has a HCI setup with a x303 cam, cobra manifold, and edelbrock heads. Just now I did a base idle reset and after the reset when I turned the car on it started up as smooth as ever but then I turned it off and turned it back on and it started surging again and stalling over and over again. When I run codes on the car it has code 96 with engine off key in and with engine on it has codes 44 and 94. Did a smoke test again and car has no vacuum leaks. If anyone could give me any help I would much appreciate Im not sure what to do next from here.

AnthonyA1234 · May 29, 2022

One thing I did notice is that when I unplug the iac when the car is idling nothing changes. Could my iac be bad?

AnthonyA1234 · May 29, 2022

Also sometimes the car won’t even crank it will just light up on the dash low oil low coolant and not crank even though the oil and coolant are fine. That’s something new that started happening today.

Gs1987GT · May 30, 2022

I suggest you go through this surging idle checklist. Start at the beginning, don't skip steps and this should help narrow down your problem.

Good luck!

Help me create the "Surging Idle Checklist"

Updated 26-Oct-2019 to clarify creeping idle RPM increase as the car is being driven. Many of you are familiar with the "Cranks OK, but No Start Checklist for Fuel Injected Mustangs" checklist and the No Crank Checklist. They are very effective in finding and eliminating the problems by use of...

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Gs1987GT · May 30, 2022

AnthonyA1234 said:
One thing I did notice is that when I unplug the iac when the car is idling nothing changes. Could my iac be bad?

When you disconnect the IAC the idle should drop, if your idle does not change, the IAC likely is not working.

There is a test procedure in the article I mentioned in my other post. I'd check for 12v at the plug first, then go from there.

AnthonyA1234 · May 30, 2022

Ok I’ll do that. I’m just a little confused on the procedure for that. Just to make sure I got it. I put the key in the ignition and put it in accessory mode. Then I put a needle in the backside of the connecter into the hole the red wire goes to, and put the red connecter of the multimeter on that. And then I put the black part of the multimeter on a engine ground. And then it should be 12v?

General karthief · May 30, 2022

Yes but you have to turn the key to the 'run' position not accessory.

AnthonyA1234 · May 31, 2022

General karthief said:
Yes but you have to turn the key to the 'run' position not accessory.

Ok thanks I did it and it was getting 12v. Hopefully the new iac will fix my idle problems

General karthief · May 31, 2022

You can try cleaning it first, I'm suspect of most parts you get today.

AnthonyA1234 · May 31, 2022

General karthief said:
You can try cleaning it first, I'm suspect of most parts you get today.

Already tried cleaning it. I’m guessing the solenoid is bad. Yea me too I made sure to get motorcraft

AnthonyA1234 · May 31, 2022

AnthonyA1234 said:
Already tried cleaning it. I’m guessing the solenoid is bad. Yea me too I made sure to get motorcraft

Found out something new just now. Just started up the car completely cold after not running it a day. Unplugged the iac right after starting it. I’ve never done this when it’s cold only when hot. To my surprise when I unplugged it the iac was actually doing something, the idle dropped from 1000 to around 650. This never happens when I unplug it when it’s hot. Usually nothing changes. Then I took it on a drive and I tried turning off the car and turning it back on and it went back to surging and wanting to stall so I guess it went back to not working. What could this mean?

General karthief · May 31, 2022

Have you gone through the surging idle checklist? You may have a issue somewhere else.

AnthonyA1234 · May 31, 2022

General karthief said:
Have you gone through the surging idle checklist? You may have a issue somewhere else.

Yes I’ve done and replaced everything on the list besides the iac and egr which will be delivering tomorrow and the o2 sensors which I plan on doing last case scenario. Any idea on why the iac is only working when the car is cold?

General karthief · May 31, 2022

You may have a vacuum related issue when at operating temp.

AnthonyA1234 · May 31, 2022

General karthief said:
You may have a vacuum related issue when at operating temp.

My car is reading codes 94/44 when running. Does that narrow it down any?

General karthief · May 31, 2022

I believe those codes are related to the tab/tad solenoids behind the passenger shock tower, are they there and vac lines hooked up?

AnthonyA1234 · May 31, 2022

General karthief said:
I believe those codes are related to the tab/tad solenoids behind the passenger shock tower, are they there and vac lines hooked up?

Yes they are all there and hooked up. Is it true that the key in engine off scanner test checks the solenoids because I hear clicking sounds and I don’t get any codes besides 11

Dan02gt · May 31, 2022

It’s possible that your throttle stop screw is turned in to the point the throttle is open enough to give the engine commanded idle without the need additional air from the IAC. If that’s the case then unplugging it would do nothing.

Get the car up to temp, unplug the IAC, and turn the throttle stop screw out slowly about 1/4 turn at the time. Give the idle time to adjust after each turn until to see ~550 RPMs. Then plug the IAC back in and see what it does.

I have my doubts that you will ever get it to run perfectly with that X cam without a tune.

I had the same issue with a much milder cam and was never able to fix it with base idle resets and playing with timing. I tried for years before giving up and getting it tuned.

AnthonyA1234 · May 31, 2022

I’ve also done smoke tests recently and had no smoke coming out anywhere besides a tiny leak coming out of the egr diaphragm which is why I ordered a new one of those along with the iac

AnthonyA1234 · May 31, 2022

Dan02gt said:
It’s possible that your throttle stop screw is turned in to the point the throttle is open enough to give the engine commanded idle without the need additional air from the IAC. If that’s the case then unplugging it would do nothing.

Get the car up to temp, unplug the IAC, and turn the throttle stop screw out slowly about 1/4 turn at the time. Give the idle time to adjust after each turn until to see ~550 RPMs. Then plug the IAC back in and see what it does.

I have my doubts that you will ever get it to run perfectly with that X cam without a tune.

I had the same issue with a much milder cam and was never able to fix it with base idle resets and playing with timing. I tried for years before giving up and getting it tuned.

Ok so I just adjusted the idle like you said. I got the idle to go to about 750 rpm and that was the lowest I could get it to go. I checked tps and all was well. Then I plugged the iac back in and it upped the idle to around 900. Checked tps again and it was still good. Then to see what would happen I unplugged the iac and it stayed at exactly the same spot. I have no idea how that’s possible haha. Then I turned off the car and pulled the negative off the battery for ten min and started the car and it didn’t even start the first crank. Started it again and it surged for a few seconds and then smoothed out like it would before. Guess I have to go back to the drawing board

Engine Surging idle issues

AnthonyA1234

AnthonyA1234

AnthonyA1234

Gs1987GT

Active Member

Help me create the "Surging Idle Checklist"

Gs1987GT

Active Member

AnthonyA1234

General karthief

wonder how much it would cost to ship you a pair

AnthonyA1234

General karthief

wonder how much it would cost to ship you a pair

AnthonyA1234

AnthonyA1234

General karthief

wonder how much it would cost to ship you a pair

AnthonyA1234

General karthief

wonder how much it would cost to ship you a pair

AnthonyA1234

General karthief

wonder how much it would cost to ship you a pair

AnthonyA1234

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Dan02gt

mazing how much gas smell came from that tiny hole

AnthonyA1234

AnthonyA1234

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Engine Surging idle issues

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Active Member

wonder how much it would cost to ship you a pair

wonder how much it would cost to ship you a pair

wonder how much it would cost to ship you a pair

wonder how much it would cost to ship you a pair

wonder how much it would cost to ship you a pair

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mazing how much gas smell came from that tiny hole

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