Engine Cold Start Issues - 86 GT

MRaburn

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The resto 86 has a cold start issue, simple one but not sure what it is at this point. Replaced pretty much every sensor accept the coolant sensor, but it reads normal when engine warms up so I assume its working OK. You crank the car the first time, it attempts to run then dies. Then second start is does an up and down idle and will sometimes level out and then good to go. On the video below, it died on the second start after rough idle. Then once its cranked again, its all normal and ready to drive. Not sure what it is.



P.S. This baby is for sell, time to get on to next projects. DM if interested and are serious, this was a long hard project.
 
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General karthief

wonder how much it would cost to ship you a pair
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It's worth a try :shrug:
but this being a new build/restore, I can't imagine it being dirty or a bad connection, but worth a try,
i reviewed the checklist on cold start surging and it talks about dirty/bad connections, to test the IAC using a light bulb to verify the computer is sending info (by way of adjusting the voltage .5-12 volts)
Varying the intensity of the light, this works if you don't have an oscilloscope, sorry you're not near me, we'd be hooking that thing up to my newly acquired old Sun Analyzer. It has a scope I'd like to test.
 
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Boostedpimp

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I had that issue on a hci car. No matter what it would die right away two starts in a row from cold then would run/drive fine after that as long as you allowed the rpms to raise and lower a few times first. Ended up being a vacuum leak by the pcv valve in the back of the lower intake. May not be your issue but you may want to hook a vac gauge up and see what reading you get and go from there. I would pull and clean the iac as well if your vacuum reading is in range
 
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Noobz347

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Also this:

This will tell you whether you still have a VSS signal going to the EEC.
Does your speedometer work? If so the gear is fine.

unplug the VSS and stick a jumper in the plug. Test for continuity on pin 3 and 6 on the ECU harness with ECU unplugged. If you don’t have it, you’ll need to start tracing the wiring back to the plug. You can start at the trans harness plug in the drivers kick panel. You can put jumpers on both sides and check for continuity at both ends to see where the break is


It's from here:

...and there is more to the convo.
 

Mustang5L5

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VSS shouldn't come into play during startup though.


I am leaning IAC. I'd clean it and perform the idle reset procedure. When they gum up from age, they get slow to respond. As the engine gets some heat into it it gets better.
 

Mustang5L5

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I can't find it now but I think VSS is referenced at startup for the 6mph tag unless you guys know of something different.

@jrichker ?

I think that's mass air only though. With speed density, the VSS is not tied into the ECU and only used for cruise control. on 86-88 non-cruise cars, the VSS isn't even installed from the factory.
 
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jrichker

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What's in the code dump?
Dump codes sticky

Look at the top of the 5.0 Tech forum where the sticky threads are posted. One of them is how to dump the computer codes. Codes may be present even if the CEL (Check Engine Light) isn’t on. You don’t need a code reader or scanner – all you need is a paper clip, or if your lady friend has a hair pin, that will do the job.
I highly suggest that you read it and follow the instructions to dump the codes. http://www.stangnet.com/mustang-forums/threads/how-to-pull-codes-from-eec4.889006/


Codes ae good, gets all 11's, but still have an idle/stall problem...

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 250,000 hits, which indicates it does help fix idle problems quickly and inexpensively.
 
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MRaburn

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OK guys, I did a code test, I have the reader... this is what I get.

12 idle out of range - i get that, could be a little lower than around 950.
94 Air Diverter solenoid circuit failure (don't know what this is)
44 Thermatic air system fault

Any input appreciated as always!
Mike
 

MRaburn

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Found @jrichker article on these 2 codes, so I'll address about the smog issues, but do not think it is my cold start problem.
Mike
 

jrichker

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@MRaburn
The 44/94 code won't affect idle or cold starts.

The 12 code may respond to the reset of base idle speed. See the Surging Idle Checklist, post #2 to reset the base idle speed to the proper value
 
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MRaburn

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@jrichker Thank you much for your assistance.

I cannot get the idle set higher than 400rpm with the screw on the TB using your post to set base idle. I have checked for any obvious vacuum leaks and will get me a vacuum tester and see. It will purr at 400 pretty much, but if i try and turn the screw any more IN which is not much because the spring is tight and bottoming out, it goes back into a rough idle, but still only sits around 400. I can get the throttle up using my foot and try and hold 600rpm just to check, and it's surging up and down trying to hold the 600. I have a Hawk RPM tester I am using.

The TB and other parts may just need a good cleaning. This is 118,000 original engine. It runs great once I get passed the starting problem and no issues at all elsewise.

Dunno.
 

Mustang5L5

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I think you are looking in the right area. Turning the screw in should just raise idle. The fact that it’s so rough makes me want to keep looking at that. You are doing this with IAC unplugged right?
 

Mustang5L5

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Can you snap a picture at the area where the set screw is? You should be able to get it up to 2k rpm (give or take) on the idle set screw. Somethings not right there.
 

MRaburn

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Here you go.. as you can see the screw/spring combo is almost all the way in compressed. If I force it tighter, I get a bad loping 400 idle, if i back off a bit I get a smooth 400rpm, then if back off more then it gets to 300rpm or so and any less on the screw then it just dies.

IMG_2158.jpg



IMG_2161.jpg



Maybe I need to get the timing back up high as before with the IAC and check timing first?

Again, this is all stemming from a bad cold start requiring a second key turn, then a lope then smooth idle and NO driving problems at all. Just a high idle of 900rpm.
 

MRaburn

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OK I took off the IAC as well just to see what I could see, it itself looks rather clean but the gasket and TB look kind of wierd, like jagged on the top hole in the TB. Does this look right?

IMG_2162.jpg



IMG_2163.jpg


Mike
 

MRaburn

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Here is TB at idle position which looks to be pretty much closed and that is with idle screw all the way in, and the second picture it wide open throttle just to see inside, looks a bit dirty, no idea if that is part of problem but I think I'll take it off and clean it anyway eh?
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