Questions About Engine Swap

Here is a case where the details matter. This thread has mentioned P1504 and P1506 DTC codes. There is a HUGE difference between the two. One is a wiring FAULT. The other could be as simple as an incorrectly adjusted idle set screw.

Yes your Mach 1 has an idle set screw.

Yes your Mach 1 has two throttle return springs.

Expect problems as long as the IAC is disconnected. It is not possible to use the idle adjust screw to correctly control the idle. If by some change you do get it to work, it will get out of adjustment when the weather changes.

Expect idle problems as long as the idle does not drop to abnormally low levels when ever the IAC is disconnected. Ideally in an application with the non black vented IAC, the motor should DIE when the IAC is disconnected.

If this were my car, I would disconnected the IAC electrical connector and then close the idle stop screw until the motor begins to run abnormally slow. IF the motor does not slow, THEN there's a vacuum leak allowing air to enter the motor from somewhere. STOP and find out where.

Then reconnect the IAC valve. Test drive. If the idle shows signs of improving, back the idle adjustment out more until the motor dies with the IAC disconnected. Be sure to turn the key off and back on after each adjustment. This is needed to reset the TPS initial position.

BUT at no point in time should you ever back the idle set screw out to the point where the throttle when closed does not POSITIVELY rest on the idle stop screw. This step is IMPORTANT.
 
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Here is a case where the details matter. This thread has mentioned P1504 and P1506 DTC codes. There is a HUGE difference between the two. One is a wiring FAULT. The other could be as simple as an incorrectly adjusted idle set screw.

Yes your Mach 1 has an idle set screw.

Yes your Mach 1 has two throttle return springs.

Expect problems as long as the IAC is disconnected. It is not possible to use the idle adjust screw to correctly control the idle. If by some change you do get it to work, it will get out of adjustment when the weather changes.

Expect idle problems as long as the idle does not drop to abnormally low levels when ever the IAC is disconnected. Ideally in an application with the non black vented IAC, the motor should DIE when the IAC is disconnected.

If this were my car, I would disconnected the IAC electrical connector and then close the idle stop screw until the motor begins to run abnormally slow. IF the motor does not slow, THEN there's a vacuum leak allowing air to enter the motor from somewhere. STOP and find out where.

Then reconnect the IAC valve. Test drive. If the idle shows signs of improving, back the idle adjustment out more until the motor dies with the IAC disconnected. Be sure to turn the key off and back on after each adjustment. This is needed to reset the TPS initial position.

BUT at no point in time should you ever back the idle set screw out to the point where the throttle when closed does not POSITIVELY rest on the idle stop screw. This step is IMPORTANT.


Thank you that will be my next task and follow your instructions to the "T", I will get back with you and let you know my findings. Hopefully this thread will help someone as well. Once my problem is corrected, I do a conclusion write up and close out the thread, well at least my part if no one has any questions.
 
Mr. Burns,

Thank you for your help, I am still working through all the stuff and made a recent discovery. I don't know if its been doing this or just started but remember when I told you the idle would spike to 2000 rpm while the car is at idle and a complete stop. I discovered something unique, I plugged my IAC back up and turned on my car to let it warm up. While the car was running for about 10 mins, the rpms spiked to 2000 and stayed there I let it run for about 5 mins. Something said check the gas pedal, when I checked the gas pedal, it was depressed as if I was driving with the cruise control on. As soon as pushed the gas pedal with my foot and made the rpms go above 2000. The gas pedal returned back to normal and my rpms when back to regular idle speed. Just to make sure this was not a fluke, I turned off the car and let sit and idle 3 times, and 3 times the rpms spiked to 2000 and the gas pedal was depressed as if I had on cruise control. I never got a check engine light and when I used my OBD II scanner to see if there was any codes maturing in the system, complete zero. Have you ever heard of this happening, when the idle would spike to 2000 in the past I am sure it was doing this as well, but now to know that my gas pedal is depressed while this happening may put a spin on things and I may have to look at more stuff or now look somewhere completely different. What is your input on this and have you heard of this before.
 
Very early on in this process you were supplied links with things to check. In those links it was mentioned to check the throttle cable for binding. As well as checking BOTH throttle return springs.

Yes there are TWO throttle return springs. One is a long straight spring and the other is a coil spring around the throttle pivot. And yes they do break. The coil spring is the one that will break but will appear to be OK. And yes they do get disconnected.

The throttle return spring is designed to positively CLOSE the throttle every time the foot is removed from the the pedal. This must happen each time. The spring must be strong enough to over come any resistance in the throttle. The throttle action needs to be smooth and positive. Any other result is a problem that needs to be addressed.

And yes I have driven a car with a broken throttle return spring. The car was nearly impossible to drive because the throttle was sooooooooo touchy. The slightest foot pressure cause way too much power to come in. I nearly ran through the shop wall.

In several other replies it was mentioned the importance that the throttle return to the SAME position EVERY time the throttle is closed. It was pointed out the importance that the throttle rest on the idle stop screw.

I'm not sure what to tell you. But it seems to me that you may be making this harder than it needs to be. Or perhaps you are over thinking this. For the most part the throttle is a mechanical device and subject to the same sort of problems that could befall any mechanical device. Don't make this rocket science until all of the low tech items have been ruled out.

I'm hopeful that your next post will have the definitive resolution to the problem. Good luck.
 
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