idle situation

[stangman16]

I haven't many miles on my '66 EFI yet as I'm trying to get all the bugs worked out. When I start my car, I have to give it some gas to keep it running until it reaches about 110-130° and then it'll idle on its own at around 800-900 rpms. Okay, so I go to the surging idle checklist and find some great info.

Tried to set the base idle speed as per the instructions below, however, I have a slightly mild (unknown specs) camshaft which is giving me a headache. When I go to disconnect the IAC, the engine dies. Found Ranchero5.0's comment (below) and I cut a little slit between the two holes but it didn't seem to help the idle at all - when I drive and shift it seems to stay at the shifting point RPM for just a second longer. Not sure if I want to cut more into it as I fear it may make the idle hang more-so then it does now.

No vacuum leaks found.

Questions:

1) Has anyone cut their IAC for a cammed engine and have any pictures? I'm thinking maybe I haven't cut enough into the IAC...

2) Why does the car die when the IAC is disconnected? (is the idle way too low or is there another problem?)

3) Do I change the 600 base RPM to 900 for my application?


stock upper & lower intakes
stock heads, 302 with 8.9:1 compression
mild camshaft that is lopey at idle
No EGR, TAD/TAB (emissions)
quarterhorse (disabled emissions)

Ranchero5.0’s comments on engines with other than stock cams:

A little dragon slaying lore here:

99% of the time on a cammed car opening up the divider between the ports on the IAC with a dremel so the motor idles at 1000rpm with the IAC unhooked, the throttle plate shut and the TPS at .98vdc fixes all surge related problems. Found about to do that on my '93 with a very mild cam and good induction it didn't like idling below 900rpm. The IAC can't react quick enough to a lopey cam induced RPM fluctuation so instead of dampening the surge it increases it. Every E cammed car I've ever worked on needed this to keep a stable idle. Similar to Fords idle bypass plate without the cobbled look. Just dremel out a little at a time till it idles around 1k. In my experience the stock puter doesn't like to idle a cammed car down low.

Setting the base idle speed:

First of all, the idle needs to be adjusted to where the speed is at or below 600 RPM with the IAC disconnected. Then the electrical signal through the IAC can vary the airflow through it under computer control. Remember that the IAC can only add air to increase the base idle speed set by the mechanical adjustment. The 600 RPM base idle speed is what you have after the mechanical adjustment. The IAC increases that speed by supplying more air under computer control to raise the RPM’s to 650-725 RPM’s

Remember that changing the mechanical idle speed adjustment changes the TPS setting too.

This isn't the method Ford uses, but it does work. Do not attempt to set the idle speed until you have fixed all the codes and are sure that there are no vacuum leaks. Warm the engine up to operating temperature, place the transmission in neutral, and set the parking brake. Turn off lights, A/C, all unnecessary electrical loads. Disconnect the IAC electrical connector. Remove the SPOUT plug. This will lock the ignition timing so that the computer won't change the spark advance, which changes the idle speed. Note the engine RPM: use the mechanical adjustment screw under the throttle body to raise or lower the RPM until you get the 600 RPM mark +/- 25 RPM. When you are done, reconnect the IAC electrical connector and re-install the SPOUT. Changing the mechanical adjustment changes the TPS, so you will need to set it.

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

 

[HISSIN50]

If you can self-tune (QH), did you raise the commanded idle in the tune?

Is the throttle valve adjusted correctly?

 

[apollo12]

All my efi motors idle between 950-1000 rpms or the car won't run right and the alt wont charge the battery.Also efi motors need good grounds and alot of them

 

[2BADSTANGS]

I have an E-303 cam in my '93 and I set my base idle at 1K, plugged th spout and IAC back in and she wanted to idle at around 14K, I then backed my idle set screw out until the car idled around 950 (without resetting base) It has been rinning beautifully for the last few days!

 

[stangman16]

If you can self-tune (QH), did you raise the commanded idle in the tune?

Is the throttle valve adjusted correctly?

Yeah I set the idle in the tune to 1500 and it barely idles at 1100. Throttle valve? (that the TPS?) I do see the TPS is off, it shows .89 at idle, and I remember something about it needing to be .98

since i'm using the QH - that means I don't have to set base idle with spout disconnected and backing out the idle screw ? Does the idle screw have any effect on how sensitive the gas pedal is? (trying to prevent an excessive acceleration ticket that may happen)

 

[HISSIN50]

Yeah I set the idle in the tune to 1500 and it barely idles at 1100. Throttle valve? (that the TPS?) I do see the TPS is off, it shows .89 at idle, and I remember something about it needing to be .98

since i'm using the QH - that means I don't have to set base idle with spout disconnected and backing out the idle screw ? Does the idle screw have any effect on how sensitive the gas pedal is? (trying to prevent an excessive acceleration ticket that may happen)

Throttle valve = throttle blade.

0.89V for the TPS is great. I would not mess with it.

I would still set the base idle to factory spec (as the EEC assumes this to have been done). Get the base idle set in the ballpark and then the EEC/tune can take over from there. If your components are functioning properly, you can set your base idle as low as you like, and then changing the commanded idle will raise the idle to where ever you like it. The fact that your car cannot achieve the commanded idle suggests there's an issue with the IAC or another component.

 

[stangman16]

Throttle valve = throttle blade.

0.89V for the TPS is great. I would not mess with it.

I would still set the base idle to factory spec (as the EEC assumes this to have been done). Get the base idle set in the ballpark and then the EEC/tune can take over from there. If your components are functioning properly, you can set your base idle as low as you like, and then changing the commanded idle will raise the idle to where ever you like it. The fact that your car cannot achieve the commanded idle suggests there's an issue with the IAC or another component.

How do you adjust the throttle valve ?

I'll try and get another IAC, suppose that is why the car dies with the IAC connector disconnected?

 

[HISSIN50]

How do you adjust the throttle valve ?

I'll try and get another IAC, suppose that is why the car dies with the IAC connector disconnected?

An improperly adjusted base idle can allow the car to crap out without the IAC.

One method of Idle setting

 

[stangman16]

Well I'm an idiot, found that my O2 harness was not connected and I'm not sure why that was. Plugged it in and it idled at about the commanded idle. Just a little off, but probably because of the small cut I made in the IAC. And it runs much better now too - LOL go figure (now that it's not dumping gas that is)

Now I gotta be careful not to break the T5 hehe

 

[bdog9seclx]

trying making sure all your grounds are properly done and all connections are tight. I had went through the whole checklist and had a wire exposed going into the computer since it was a v6 upgraded to 5.0...like your isnt it a efi upgrade. hope helps surging is not fun to tackle