How can I adjust the idle RPM on a '95 Bronco? I'd like to drop it a little.

TIA

 

The idle is non-adjustable. It's controlled by the computer.

 

If you have an adapter spacer between the IDLE AIR CONTROL and TB. you can adjust it. Maybe your timing setting needs adjusting +10 degrees without spout.

 

Andym is right on the computer controlled idle. If the idle seems high to you, check for vacuum leaks. They allow additional air into the intake creating greater flow and thus higher RPM's.

 

OK, maybe I have to ask this question a liitle differently then.
And make it into 3 different questions.

a) Is there a way to trick the computer into to lower the idle?
b) is there some kind of tool that would allow me to repogram certain parameters?
c) is there some documentation on the computer, or it's all proprietary?

TIA

 

How does the throttle body spacer work? What does it do?

TIA

 

I would have to agree with Greystreak, sounds like a vacuum leak. Did it just start having a high idle or has it always done it? What is the currant idle at now?

 

A) none that I know of that will not result in problems with the rest of the computer controlled functions.

B) Performance chips and tuning software computers but I highly doubt you can lower idle speeds without affecting other conditions as already stated.

C) Not that Ford is gonna hand out just yet. The EEC-computer software is there baby. If you are looking at modifying or performance tuning Ford Fuel Injected engines in general I recommend Motorbooks, Powertech Series: "How to Tune & Modify Ford Fuel Injection" by Ben Watson.

 

What is your current idle rpm and which engine are you running?

 

" Is there a way to trick the computer into to lower the idle?"
Don't think that you can override and "trick" the computer by mechanically adjusting the actual throttle cables. It might alter it for a minute or two but the computer will relearn it and the idle will go back to wherever it usually is. I learned that the hard and frustrating way, not with my Bronco but on another vehicle long ago.

But where does yours idle anyway? My 1990 5.8 with 130K idles right around 700 rpms and generally the motor is not even detectable at idle. It literally idles so smoothly most of the time that there is no change in feel between the engine running or shut off! If the radio is turned up then the truck may as well be turned off when it idles because you can't feel a thing and you can't hear it. It idles more smoothly than most new cars and trucks and the tachometer needle is rock steady. So I would imagine that 700 is about right.

 

Engine is 351W, and when it was tested (emission test) it was well over 600 rpm. (690 in the test sheet, but it was less than that) Still within the acceptable range (for emission purposes) but way too high for my taste. It always seemed a little high, but I never bothered with it.

For comparison, I had a '72 LTD with a 351, and that was around 500 rpm.

 

Don't think that you can override and "trick" the computer by mechanically adjusting the actual throttle cables.

Actually, I'm thinking about more sinister things like modifying sensors' output by using a carefully selected pullup or pulldown resistor, or put a variable frequency multiplier between the rpm sensor and the computer -- when the engine is at, say, 700 rpm, the computer would see data that indicates 800 rpm.

The pullup/pulldown modification is a piece of cake, but the frequency multiplication (or addition) would be a little tough.

 

Yeah, you are talking about the difference between a carburated big block and a fuel injected small block. The 351 in your LTD was more than likely a 351M not a 351W. 351M are smaller bore big block engines. My 69 Caddy idled @ 550 in-gear w/ a 472 under the hood. Big blocks can idle down in the low 6's and high 5's because they start out with more torque than a small block and the drag from these components and the drop into a moving gear won't be enough to kill it. Small blocks need the higher RPM's because they lack the torque.

In park, an EEC-IV-equipped 351 should be turning something in the neighborhood of 700-800 RPM. It will drop to about 600-700 "in gear". Any slower and the drag from power steering, A/C (if its on) and alternator will combine to bog it down enough to kill it. Try running with the IAC bore 50% clogged and you will see what I mean.

 

Today's vehicles idle higher than the old land yachts of the sixties and seventies. Your truck is actually a tad on the low side for a computer controlled, fuel injected Bronco of your year. Why do you feel that it is too high? Is it just the number that bothers you since you are used to your old LTD, or does it not "feel" right to you?

The 700 RPM idle on my Bronco is when it is at operating temperature and in drive. It's about the same, or just a little bit higher, when in park. Upon the first start in the morning, it idles at about 1,000 rpm for about a minute or a little less and then drops to operating rpm's and stays there. And ever since I replaced the IAC, it maintains a consistent idle when the A/C compressor is cycling on and off.

BTW, in reference to your old LTD, GS's old Caddy and many other old land yachts that I've owned or worked on over the years, I used to find it rather amusing sometimes, looking at the engine while it was idling and thinking that it seems like it is just one rpm from stalling. Sometimes I hardly believed that they could stay running like that, you could even watch one of the individual fan blades go around and around and keep your eye on it. But that's how there were made; don't compare your Bronco to that. At your reported rpm's, there is nothing wrong with it. Lowering it further could cause overheating, lack of vacuum, lack of alternator charging, or low oil pressure. I suggest to leave it like it is. If you don't like it, try changing the cam for a different feel.

 

I disagree. Big block or small block, I think a 351W should be able to idle just fine at 600 rpm or below -- it got 8 cylinders, after all. Of course, one way to prove this is by actually doing it and show that it works.