Cold Start And Stalling Sometimes When Coming To A Stop

5.0 Swapped

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Hello All,

New guy here, but have been messing around with Fords for a while. This is my first true venture in the EFI realm. Anyways I have done tons of reading and worked on most issues people recommend on this site. I have done a 5.0 swap...engine came from a 91 T-bird, but using the SN95 EEC and a new T5Z transmission. What is happening is on a cold start up, it takes 2 to 3 tries for the car to stay running (it fires up immediately each time). Once it actually wants to stay started, the rpms will rise and then sharply fall to about 500 and then pick back up again to about 1,000.....then it settles down to 750. Also at random I will come to a stop and the car will die (yes the VSS is connected). Now let me list all the new parts I have installed....TFI, 2 distributors (One Cardone and the latest is a Richporter), Motorcraft TPS and IAC, ECT and ACT sensors (checked voltages and ohms), fuel pump, FPR, 65mm Throttle Body, MAF, rebuilt injectors, plugs, wires, etc. Before I was chasing down 2 codes for the TPS and the ECT. TPS I was using a Standard Products one and switched to a Motorcraft (fixed code) adjusted to about .85v, then put new harness on ECT as it was corroded and the ECT code went away. So now I no longer have any codes other than the fan ones and EVAP Canister(which are not connected), getting 11 code for the KOER and got a 9 for all 3 cylinder balance tests. Anyone have an idea where to check next? I keep wondering if I have a stray vacuum leak somewhere by chance. All hoses are new....EGR is blocked off and all intake hoses are blocked or connected. So basically when started, the car will not immediately idle up to stay running and then go down once warmed up like newer cars do. To note I am running a tune that took out the EGR and other items so they no longer throw a code. Car runs same with or without the tune so I know that is not the issue. The tune is still the baseline with minor changes. Thank you for any input.
 
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5.0 Swapped

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To add I have run through the base idle setting procedure about 5 to 6 times. Some reason I cannot get it to start and stay running on its own with the IAC unplugged. I can butterfly the throttle and it will stay running, but once I stop it will die. This is on a cold engine I attempted the last one on. Thanks
 

Mustang5L5

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Which wiring harnesses did you use for the swap? I'm wondering if the mismatch of components is causing an issue somewhere.

Are you using the 91 tbird engine in as-in condition with the Sn95 style accessories and intake? Which SN95 ECU are you using? And what wiring is running the engine?

If you unplug the MAF and start the engine cold, does it make a difference?

Have you run through this checklist yet?
https://www.stangnet.com/mustang-forums/threads/help-me-create-the-surging-idle-checklist.698148/
 

5.0 Swapped

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Thanks for the reply Mike. The lower was untouched as it has the forged pistons, but had the heads rebuilt. It does have the SN95 accessories and the stock shorter intake (due to clearance). I am using the T-Bird wiring harness as its the same pinout as the SN95. The only thing I changed from it was to move the ACT to the cold air intake instead of the block location. I am using the T4M0 EEC.
I was questioning the MAF as even though it is new its a Dorman brand. I actually have a Motorcraft on the way that was from a running 94 GT. I seem to think one time I did start the car with the MAF unplugged and it started right up (many tests ago). I will try that again when I get home this evening to test. The car runs great though when you are driving. To me the car seems to be running rich, but its hard to tell as I have no cats. I have read the 5.0 with no cats makes for a stinky situation. I am going to see about having some high flows installed soon. Also the O2's are brand new as well. Thanks!
 

5.0 Swapped

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Okay so I was just able to test and found out yes, it fires right up with the MAF unplugged after sitting overnight. Turned off the engine, plugged it back in....took 3 tries for it to stay running. Aside from maybe a bad MAF, anything else I should look for? I hooked a vacuum gauge up to it and it stayed at 17. It was a little jumpy because you can hear my idle is not totally smooth. When I did the quick rev test it jumped very fast going to zero, then back around to 25 and went back to 17.
 

jrichker

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You guys with idle/stall problems could save a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first two posts have all the fixes, and steps through the how to find and fix your idle problems without spending a lot of time and money. It includes how to dump the computer codes quickly and simply as one of the first steps. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix. :D

It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 200,000 hits, which indicates it does help fix idle problems quickly and inexpensively.
 

5.0 Swapped

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Thanks Jrichker as yes I have poured over your posts and also the checklist as listed. They do come in handy and helped me fix a few things. As noted above, I did have codes before, but all the codes attributed to this are gone. The only thing I have not tried is testing the MAF wiring as that will be a bit tough how the computer is mounted. Since I do have a knock off Dorman MAF, I will be trying an original Motorcraft one to see if it helps. Unfortunately I had to buy many new parts because the original engine was in a barely running state....though I knew that going in. Thanks
 

5.0 Swapped

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Well, drove the car around this weekend for the first time and of course it ran like a scalded dog. I don't believe that new Challenger knew what to think when he saw a Miata right on his tail when he had just passed me doing about 50 and I at a stop sign. :) The bad news is I started fooling around with the idle more and testing MAF clock positions to stop the random stall I keep having (probably happens 1 to 6 times stopping). The MAF clocking made the EEC mad. Got the idle set great per the base idle reset instructions, but the car would keep going steady without any pedal on a test run. Assuming the throttle blade is cracked open a little too much the way I set it, yet when parked the car seemed to like where it was set. Upon returning home to make more adjustments, the car stalled. Fired it right back up and then it stalled after a minute of running. Popped the hood and could smell something electrical burning. Went around checking things and I could not touch my remote mounted TFI at all (that's what a lack of thermal paste will do kids). I believe it burned up (was the original Motorcraft I had as the SMP one didn't seem to run right). Sure enough put the SMP one on and the idle was garbage/shaking engine and was seeing a random 02 left side rich sensor code I never got before. Anyways, Motorcraft MAF on the way along with a new Motorcraft TFI. Will keep the thread going for others that may have a similar issue and can perhaps gain info from it. I hate to read all these posts and then the person says they are going to go test something and they are never heard from again. It's like they all went out on a trial run and never made it back home. As a note: All I can say is make sure to buy ONLY Motorcraft parts.
 
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As promised, I already have an update. Unfortunately I am not sure which part was giving the most trouble, but I believe it was the MAF. Put on both the known good Motorcraft MAF (ditched the purchased new Dorman) and put in the new Motorcraft TFI (ditched the purchased new SMP). Guess what happened next? I now have a car that idles like it should and also revs immediately upon starting like it's supposed to. Took it out for a drive and it didn't die once. Each time I slowed the car and pushed the clutch in, the car would gradually decrease RPMs and land at 750 like it should. Finally! I was about ready to rip the EFI out and put a nice carb in its place. So there ya have it. It was the MAF, TFI or a combo of both. Burning the original TFI up may have been a blessing. :)
 
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