Ken:

>>>>
The throttle return stop prevents the throttle plate from contacting the bore and sticking closed.
>>>>
To minimize the closed plate air flow, a special coating is applied to the throttle plate and bore to help seal this area.
>>>>

Don't you think that the above two sentences almost contradict eachother? It may stick if the seal is too good.

This is supposed to mean that the PCM will determine the idle speed using the IAC, right? Okay, this could mean that if I backoff the screw to close the throttle plate, the PCM should increase the duty cycle of the IAC to maintain a certain RPM. This could account for my duty cycle at idle being 0-1% but would it go up to 30-35%??

Interesting, but they still don't give you a procedure to adjust the stop screw. If the screw is used more like a overtravel stop so the throttle plate doesn't close too far, you'd think that the test for IAC functionability wouldn't say, engine slow down but only stall when the connector is pulled!!

It's a 7/23" hex on that adjusting screw but very thin. You have to use a 1/4" ratchet with socket but because the hex is so thin and sooooo close to the fan pulley, you end up cocking the socket which ends up pulling off! I got where I adjust the screw with the engine off, instead of losing a finger or driving a tool into my radiator

 

Bill,

I think they are tring to say that the stop just holds the plate very slightly open and the coating might be a non-stick type of material to also avoid sticking. This would agree with the other purpose for the coating, keeping dirt from sticking to the TB.

If you close the plate the duty cycle should go up, I think. I would think that since it is slightly open that is why you may not stall without the IAC.

I never took a close look at the screw but I would do it with the engine off since it seems to be very tight there.

Now the new question, why is there a duty cycle for the IAC at speed, when the throttle plate is open. Wouldn't you think the duty cycle would be 0 once the throttle plate is opened.

 

Ken:

Hmm, that might be just so it can be used for deaccel. I don't know if you ever felt that little jump when your coasting down. I've talked to F-150 owners who felt the same thing. Now that I've learned a little, I'd have to say that it's the IAC doing that.

They might want to keep it in the mist of a duty cycle, in case your throw a heavy load, like A/C Max. instead of coming from 0%. Just guessing here

 

Ken:

I got out there today to check the IAC duty cycle with my OTC DAT. I connected my OTC breakout box, started it up and let it warm up a bit. I come back, geez, why is it running so ruff? I could smell gas too! I had the scanner connected and ran a scan. I get P0353, Ignition Coil C Primary/Secondary Circuit Malfunction! What did I do wrong? I got that code once before. I removed the breakout box, no more code!

I let that go and moved on to the IAC duty cycle with the OTC DAT. I couldn't get it to read anything. I called them up and mentioned both problems. The DAT duty cycle problem is going to their engineering department. I told them that I check for open wires and shorts on nearby pins close to the ones that go to the ignition coil. Didn't find anything wrong. I'll have to reconnect and check back to the coil connector.

Wondering why they refer to the ignition coil as "C" when they are numbered in the electrical manual and not lettered?

So now every piece of test equipment I bought has problems! Ain't I lucky?

 

I think it's the equipment causing the issue since it runs good when it's not connected and you got me on the "C" thing. At least you have the good equipment, sorry about the problem too.

 

Ken:

Yep, OTC has been around for years but like anybody else, problems do happen. For sure it's the breakout box giving me the DTC and that's probably why I lite my CAT up that one time too.

I connected it again but not to the PCM and checked back to the coil connector. No shorts or open wires either. Maybe I should have tried something with it connected to the PCM. Wonder if I could read anything during KOEO? I'd have to look at the book.

Here's another tidbit. The pinout for the coil connector in the Power Control Manual and what's in the Electrical Manual are different. The electrical manual is wrong. Who would number coils 1,3,2 from left to right?

We'll see how OTC is answering to my problems compared to AutoXray whom I'm still waiting on.