Electrical 1987 - IAC valve (Diode & Ohms)

7991LXnSHO

wanna catch the space herp
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Sep 1, 2010
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Consider building a smoke machine. Not that complicated to make and comes in very handy.


View: https://youtu.be/crc6CJ_ni2w


I’m actually building one right now. Just waiting on a few parts from Amazon to show up.

How do you fell of your homemade smoke machine is burning up? :scratch: :jester:
The PVC case on the videos I have watched made that a serious question.
 

R82148V

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May 26, 2020
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UPDATE

I was able to confirm that the Cruise control Servo and brake booster holds vac very well. No leaks there.
I did however find a major leak within the HVAC line and narrowed it down to the line that is inside the car. I capped off the main line from the vac tree and retested the idle.. WOW what a difference in idle! No surging or hunting or anything! I went to set base idle again and was able to get the idle lower with the IAC unplugged but still not low enough. I looked for more vac leaks and discovered a slight leak at the EGR valve. Between the plunger and diaphragm. I sprayed a little brake cleaner in there while it was running and it changed idle speed. A new EGR should be arriving today from RockAuto.

I also performed a KOER test for codes. Came back with code 44 & 94. Tab and Tad solenoids are working, crossover pipe and engine ports are clean. Bypass and Diverter valves are functioning when applying manual vacuum. Air pump is moving air when car is running but I dont know how much it should be. When I went to check on the vac lines coming from the tab and tad solenoids, the hard lines snapped. So I'm guessing vac leaks there are causing the 44 & 94.. I cant think of anything else.

Any other ideas?
 

Mustang5L5

Put lubricant all over the balls
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Biggest culprit is the ports inside the heads themselves get clogged up. The path runs front to back through the head with perpendicular pathways to the exhaust ports.


And yeah...it's amazing how sensitive these cars are to vacuum leaks, especially 86-88 speed density cars as their fuel/timing curves are based primarily on manifold pressure. A small leak will change that
 
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R82148V

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May 26, 2020
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Biggest culprit is the ports inside the heads themselves get clogged up. The path runs front to back through the head with perpendicular pathways to the exhaust ports.


And yeah...it's amazing how sensitive these cars are to vacuum leaks, especially 86-88 speed density cars as their fuel/timing curves are based primarily on manifold pressure. A small leak will change that
I had no idea, these years especially, were that sensitive to vac leaks. That's all you hear/ read about is vac leaks if you have surging, hunting idle. Everyone was so right!

That must be basically impossible to fully clean out.. I tried cleaning the openings to the heads about 3 inches in.. That was as far as I was able to reach..
I guess as long as air is being pumped into the exhaust, Shouldn't worry about the codes so much?
 

Mustang5L5

Put lubricant all over the balls
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The answer to that question all depends on if you have cats. And if you do, do you have a stock 4-cat H-pipe or 2-cats?

If you don't have cats. None of that stuff matters at all. Plug it all up, disconnect the TAD/TAB and live with the codes. They don't set off the CEL and don't alter the way the ECU functions.


If you have a 2-cat H-pipe, it also doesn't matter. Here's why. The air pump system supplies o2 to the converters to make them more effective. These old cats relied on heat and O2 to be efficient. When you first start a cold Mustang, the cats simply aren't warm enough to do their job. SO ford added two small cats close to the headers so they would heat up quickly and do their job more efficiently. As a result, when you first start the car the TAD and TAB direct the airflow to the heads (specifically the exhaust ports) where the O2 flows into the headers and down into the first set of cats to help them be more efficient.

Once the vehicle is warmed up, the TAD switches the routing of the air from the air pump down to the lower set of main cats and this is where it will stay until the vehicle cools down again. This is why the heads and crossover tube tend to fill up with carbon. They only flow for a short period of time.

For the 2-cat pipes, you replumb the air pump if you'd like to just function for the main cats. This all depends on the setup of course, as my catted Bassani X-pipe has the air pump tube enter AFTER the cats rendering it completely useless. But if you wanted, you can just remove the diverter valve and the crossover tube plumbing and just cap off the TAD vacuum port. Leave the TAB and bypass valve in place and the car will just enter bypass the air to atmosphere or send it down to the H-pipe.

If you don't want to deal with the codes, a pair of 65-90ohm resistors should take care of the KOEO codes (81 & 81 i think) but you will still get the 41 & 91 when you do the Engine running codes.

Not a big deal.


Long winded i know, but helps to know how the air pump system work and what it's intent was.
 

R82148V

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5L5, I love all your info. I’m learning a ton! I really do appreciate it and your time.

I just looked and I have the 4 cat H-pipe.

I’m wondering if perhaps I have the tab and tad vacs switched. which is the tab and which is the tad? My haynes manual shows the tab is closest the fender and tad is closest the engine? Every where I look online though they are saying the opposite.
 

Mustang5L5

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Per the factory EVTM

TAB is towards the outside of the car and TAD is closest to the engine.

TAB is white/red wire to pin 51 on the ECU
TAD is light green/black wire to pin 11

Those are ECU controlled grounds. The other wire should have constant 12V



1638408443753.png
 
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Mustang5L5

Put lubricant all over the balls
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I dunno if you've seen this diagram, but this will visualize the air pump system. Flow is to the heads during warmup to feed the first cats (not shown here) and then it's directed to the main pair of cats when the vehicle is warm. I believe at WOT, the bypass dumps all the O2 to atmosphere.

1638408995030.png
 
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R82148V

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May 26, 2020
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I dunno if you've seen this diagram, but this will visualize the air pump system. Flow is to the heads during warmup to feed the first cats (not shown here) and then it's directed to the main pair of cats when the vehicle is warm. I believe at WOT, the bypass dumps all the O2 to atmosphere.

1638408995030.png
Excellent diagram! After studying this, the factory EVTM pic you sent, using the wiring diagram and item description pic from my haynes manual, I come to realize the tab and tad wiring and vac lines were reversed. Your stating TAB is towards the outside of the car and TAD is closest to the engine. My manual showed that too..
1638472744569.png

Per the wiring diagram from Haynes, had the wiring reversed.
I had the RED and GREEN wires going to the TAB.. In this diagram, it shows the RED and GREEN is supposed to go to the TAD.
Doing KOEO, I always pull Code 11, but KOER its always 44 & 94. Cant wait to try this reversal tonight!!

1638472891263.png
 

R82148V

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May 26, 2020
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UPDATE

So I was able to check all the wiring from the PCM back to the TAD. Verified the tad was receiving 12 volts and that the solenoid worked by grounding it out. You can hear it clicking on and off. Started the car and was able to confirm both TAB and TAD valves were receiving vacuum during warmup. SO the TAD solenoid is confirmed working! I think it was a bad connection on the PCM pin that did it.
Anyway, I ran the car to opt temp and performed the code reader. It still came back with codes 94 and 44 even though the tad is working.
I checked the air pump and it blows air. How strong it supposed to be I have no idea but you can definitely feel air blowing out. TAB AND TAD valves open and close without issue when putting a hand vac to them. Crossover tube is clear and clean. I took off the crossover pipe last night and confirmed.
The ports on the back of the heads are clean but only about 3 inches in. I was able to use a long drywall screw to see if its still packed in there and it is. I can screw in the screw and pull out this moist black crud. I have no idea how that stuff gets packed in there. But I'm sure that is my issue.

know the ports run from back to front of the heads and with the ports being so close to the firewall, how do you clean that stuff out!
I think I read somewhere that you can clean out the ports from the front of the engine too? Is that true and where do I look?
I was also looking for a diagram of what the ports look like.
Any ideas!


Thank you!!! :)