Confused to a certain degree does this mean some have 3 wires going to the harness? I have to look at mine but will cut out the diode and maybe this will fix my strange idle
Confused to a certain degree does this mean some have 3 wires going to the harness? I have to look at mine but will cut out the diode and maybe this will fix my strange idle
Ben
67 camaro convertable project
86 gt project (for sale)
90 porsche 911 (sold)
09 toyota tacoma
07 burb
mustang parts for sale http://vb.foureyedpride.com/showthre...42#post1406542
No because power still needs to be supplied to the IAC, all that is being stopped is any communication between the diodes.
85 GT Vert' (CFI converted to EFI), 306 TFS 170's, Systemax II, Lunati cam, 8.8 w/3.73, Ford Racing T-5, AFM Powerpipe
317 rwhp 304 rwtq
^ my thoughts exactly. Once I opened up my harness and saw how the dioode was in there, it was a no brainer which to connect back.
1986 CHP SSP Coupe
Okay, I just want to back up a little back after re-examing all of the posts. I think I may have been misunderstanding the initial post. It sounds as though you have an upgraded IAC that already has the diode built in AND you were using an older style harness that had an inline diode. From what I am gathering, the inline diode was battling with the built in IAC diode so you simply inactivated the inline harness diode to let the built in IAC diode do its thing unopposed. On my bone stock 1986 GT, the only diode that is there is the external inline one. My question now is, do I really have to do anything with this external diode if I am running the stock 1986 IAC? It would seem that the answer would be no. From what I gather, the TSB may have been to address IAC problems if someone upgraded to the newer IAC but left the other diode in place also. In short, the mod you described only needs to be done if the IAC is a newer replacement one and that this really doesn't apply to original stock 1986 IAC, which doesn't have the diode built in.
Last edited by HAD85B4; 06-14-2012 at 01:12 PM.
You got it....
stock IAC=leave harness diode ALONE
newer model IAC AND 86 (possibly early 87)=eliminate harness diode
Again this only applies to my car which is the 86 GT harness V8 after I had exhausted all the high/surging idle checklist possiblities.
85 GT Vert' (CFI converted to EFI), 306 TFS 170's, Systemax II, Lunati cam, 8.8 w/3.73, Ford Racing T-5, AFM Powerpipe
317 rwhp 304 rwtq
From what I have read, the newer IAC's with the built in diodes started around 1990 model year. Do some of the 1986 and 1987 cars have these from the factory or are they replacements that may have been done for idle problems?
My Ford tech buddy and I came to the conclusion that Ford probably saw money savings as they moved into the new EFI era and streamlined stuff such as this later on during the learing process. Hence now all that is available is the IAC's with the diode built in as it wouldnt be cost effective to build each part that is the same except for one thing internally.
85 GT Vert' (CFI converted to EFI), 306 TFS 170's, Systemax II, Lunati cam, 8.8 w/3.73, Ford Racing T-5, AFM Powerpipe
317 rwhp 304 rwtq
is there any way to tell if the iac has the diode built in?
00 GT Terminnated
86 GT Vert 9L
00 SVT contour
Past cars
92 coupe 2.3t conversion, 85 SVO 1C, 87 turbo coupe 1C, 88 turbo coupe 1C,98 svt contour black
Yes. A diode is like check-valve for electricity.. it allows flow in one direction only. Use an ohmmeter to check the resistance of IAC valve. If it has a diode in it, you should get a reading with the leads hooked up one way (no idea what normal spec is - probably like 5-10 ohms) and a very high reading or OL (out of limit) or open circuit with the test leads switched. If you get the same reading in both directions, there is no diode.
Last edited by tripice351; 06-15-2012 at 01:52 AM.
Marc aka tripice351. 84.5 GT-350 2.3T.. and now, 1982 GL coupe.
Wow this was great info thanks. I did inspect mine and it had no diode (harness) and my harness came off of an 87 I will have to check the IAC to make sure it is correct
Ben
67 camaro convertable project
86 gt project (for sale)
90 porsche 911 (sold)
09 toyota tacoma
07 burb
mustang parts for sale http://vb.foureyedpride.com/showthre...42#post1406542
I just tried this and it didn't work? I pulled the pins out of the connector, switched them to opposite sides, plugged it back in, and now the car wont start?
Could this have blown one of the diodes? Any Ideas on what to do now?
Last edited by 86 GT Vert; 06-15-2012 at 05:11 PM.
1986 GT Convertible Daily Driver.
Which IAC do you have? When I unplugged my IAC to rule it out it wouldnt run. Id say you have the original style IAC that doesnt have the diode thus you need to put it back. Just remember this is the last resort after exhausting all other poor idle contributors.
85 GT Vert' (CFI converted to EFI), 306 TFS 170's, Systemax II, Lunati cam, 8.8 w/3.73, Ford Racing T-5, AFM Powerpipe
317 rwhp 304 rwtq
Yikes. As I noted above after re-reading the original post, the fix he outlined are for cars that are equipped with an external harness diode AND an upgraded IAC that has the built in diode. Does your car have a stock setup? If so, chances are your IAC doesnt have the built in diode and you will probably have to put things back.
+1.....I know when I was narrowing to the IAC as the suspect area like I said when I went with it unplugged my car would not run but I have far from stock so Im sure that was part of it.
I will add another bit of help on leaky seals, oil in the intake, etc. So I did some reading and was ready to set up inline filter catchers to stop oil getting sucked in the intake. I have the baffles removed for my stud rockers for clearance. I changed out to stock Ford PCV for the one for the 70 Boss 302 which has much lower vacuum. My vacuum was on 5-7 when I measured it which is WAY lower than the stock PCV is meant for thus, tons of oil was getting pulled because it was never closing. So having the incorrect PCV for your specific engine is essentially a controlled vacuum leak. Just thought I would add that from recent discovery before this one.
Last edited by QisJob1; 06-15-2012 at 10:17 PM.
85 GT Vert' (CFI converted to EFI), 306 TFS 170's, Systemax II, Lunati cam, 8.8 w/3.73, Ford Racing T-5, AFM Powerpipe
317 rwhp 304 rwtq
I have the diode. I believe I have a later iac but need to check the ohms.Maybe tomorrow.
Stan
1986 Ford Mustang Saleen #80 Gray/gray
1986 Mercury Capri ASC McLaren Coupe#20 Black/silver, gone.
1985 GT Silver/gray T-top car, gone
1985 Canyon Red Turbo coupe, gone
So after countless attempts at fixing the hunting/surging idle on my 86 I found this thread. Removed the diode (had already replaced IAC) and now my car idles like it should. I went the route of snipping it out and soldering the wires back together, hopefully my sketchy idle problems are finally gone.
Where about is diode located. Have idling problem. Iac/act is located in cold air intake.
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I'm curious about this myself...
Brad
'79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
'17 Ford Focus ST
'14 Ford Fusion SE Manual
After removing cover this what I found. installed new idle air control about one month ago. Should I cut red and reconnect them and just remove yellow.
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Found this diagram today
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Interesting! So, in theory since my harness is 1990MY, it shouldn't have that.
Brad
'79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
'17 Ford Focus ST
'14 Ford Fusion SE Manual
Brock
1984 Mustang LX Convertible 3.8L V-6/Auto (SOLD)
1984 Mustang GT Hatchback 5.0 V-8/5 Speed
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