Electrical Ecc overiding base timing?

Ok so when I got this car it had a high idle and stumbled really bad. I found several vaccuum leaks and things started to smooth out a bit, but still high idle. I checked the timing and it was way advanced at base. I pulled the spout and the IAC, backed the throttle screw all the way out and set timing to 10. I tightened the hold down bolt, double checked the timing, shut off the engine and reinstalled the spout. I then unplugged the battery for 15 min.

I came back and plugged the battery back in, IAC is still unplugged. Started the car and yet again the idle was up to 1000 and timing nearly 29 at "idle". So I figured the distrubutor had slipped. I pulled the spout while out and it instantly settled back down, 10 degrees and 800 rpm.

I thought that was weird, so then I changed nothing and plugged the spout back in and it reved up again, timing went up to 29 and rpm at 1100.

With spout out, IAC unplugged, TB screw backed all the way out and timing set manually at 10deg, she purrs, smooth no surge. Its almost like the ECC is giving advance commands at base idle. The IAC is new BTW

What's going on here?
Am I not following the post timing procedure correctly to get it to"take"?
Something funky with the ECC?
Do I need to have the IAC plugged in when setting base timing?

If I understand the spout correctly, when inserted, it allows the ECC to control advance as you increase throttle. Why would it advance timing at idle when I reconnect it?

General karthief said:

This should answer all your questions on timing, base idle reset

Help me create the "Surging Idle Checklist"

Updated 05 July 2022 to add rough idle when cold and smooth idle when up to normal operating temperature. See the EGR tech information, section #15 for more help. Many of you are familiar with the "Cranks OK, but No Start Checklist for Fuel Injected Mustangs" checklist and the No Crank...

www.stangnet.com

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thank you and I have defiently read this before, but thought that my issue was different.....however if the ECU adds timing once the spout is plugged back in as 5L5 amswered, then it is adding too much and making the idle too high. So I guess the question is, why would the ECU be adding so much timing?

I saw this:

"An engine that whose idle speed cannot be set at 600 RPM with the IAC disconnected has mechanical problems. Vacuum leaks are the #1 suspect in this case. A vacuum gauge will help pinpoint both vacuum leaks and improperly adjusted valves. A sticking valve or one adjusted too tight will cause low vacuum and a 5"-8" sweep every time the bad cylinder comes up on compression stroke. An extreme cam can make the 600 RPM set point difficult to set. Contact your cam supplier or manufacturer to get information on idle speed and quality"

Can I assume that the author means 600RPM, IAC Disconnected and Base timing set at 10 deg? With the timing set at 10, I was at 800. I never tried to set the advance at 0 or aim for a specific RPM, should I try to re-time to 0 advance and aim for the 600 RPM and then just let the ECU add back in the timing hopeing it lands at 800ish? Is the 200 RPM difference at 10deg indictive of a mechanical issue as described above?

I know I have an issue and I certianly had lots of vacum lines missing when I got the car but I really thought I got them all. Sprayed carb cleaner all over the lines and no changes in idle so felt good about that but I guess smoke machine is next? Unless I should be looking elsewhere?

General karthief said:

Base timing is 10*, anything less will cause issues, do the checklist.

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Thank you, so then I ought to be seeing ~600RPM at 10deg advance and I am 200-250 higher than that. I will be cobbling together a homemade smoke checker since the carb cleaner trick may not have worked.

Mustang5L5 said:

The timing is not where I would focus here to start. I'd go the checklist. Pull codes, smoke test for vac leaks, etc.


More details on the car? Year? trans? Is this a swap car? (4 cyl to V8, AOD to 5-spd) or any other relevant details pertaining to wiring/ECU changes.

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The car is molested. It is a 92 hatch but what I know is that it has a transplanted 94 or 95 motor. Visual signs back that up as the block was painted blue semi recently. The guy I bought it from is not the guy that did the modifications so I cannot ask. The diagnostic plug is not where it should be, I need to check in the inner fender to see if it was placed there for some reason as the wire loom is there but it is tucked into the fender (no check engine light which I am also suspect of). EGR was deleted and all the sensors are new including a aftermarket MAF. I have not yet taken the kickpanel off to see if it is running the stock computer but I am starting to wonder. When I got it there were several vacum lines just missing, not one on the FPR, open line on the old AC system that is deletedish one sticking up from the canister (unknown if connected but capped just in case). Once I go tthe vaccume lines capped or run it smoothed out a lot but not all the way, when I was timing it though with the IAC unplugged it got really smooth. I knew it would be a discovery project when I got it but it has no rust and the interior is complete and in good shape so I figured it was worth the risk.

loped and idled high, sounded almost like a miss but runs great at WOT, was defiently running rich before started in on it, could smell it (could have been no vacum to FPR).

Could a cam be causing this? Some kind of plug in chip? I think ill check the computer tonight after work.

Mustang5L5 said:

ECU mismatch, and various wiring not hooked up could cause hanging idle. Specifically the NGS on top of the T5 and clutch pedal not being connected and using a Fox ECU. Also, not having the VSS sensor hooked up could cause hanging idle (or stalling).

If it idles high and sounds like a miss, it may very well be a vac leak too.

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Thanks, this was why I was strongly considering swapping it all out to carb. I'm not racing it, I'm not worried about mileage changes, It's not an "investment". I'm registering as an antique so just driving on wekends and car shows. Its just a toy so by the time I get a new wiring harness alone I could buy all the needed parts for the carb conversion new. Everyone is very anti efi to carb but in this case, it may make sense. I'm trying to hunt this down first, obviously. But if ole boy already cut out my DX port and used a fox ECU on a SN95 engine, yanked out the A/C, deleted the EGR, and who knows what else.....then may not have much to lose.

Ill keep hunting it down as is though for now. Need to make a redneck smoke checker.