High Idle:'94 Ranger 2.3L

Doug Funny · 02-16-2009, 10:52 AM

I have a '94 Ford Ranger that has a very high idle. The only way to reduce the idle is to unplug th MAF sensor but then I get a check engine light and I have to screw the idle screw all the way in to keep engine running along with bad gas mileage. I don't think the MAF sensor is the problem and I have checked for vacuum leaks (found none) but I think I may have a leaky intake manifold gasket. The reason I think I have a vacuum leak is when I depress the brake pedal it almost feels like the engine is not running only not quite so hard. A gasket set is only $10 but was wondering if there is anything else I should check before I spend a couple hours replacing the gaskets?

BroncoJoe19 · 02-16-2009, 03:38 PM

This may help.
Checking for vacuum leaks.
Some of the sensors and some of the actuators either read the amount of vacuum, or use vacuum to move controls, therefore it is important to the proper functioning of the engine that your vacuum system is fully intact. Otherwise one may get codes falsely indicating that there is a problem with a controller/actuator, or a sensor when in reality it is caused by a lack of vacuum.

Look at your rubber vacuum hoses (they are about 1/4 - 3/8 inches in diameter, if they are dry rotted or cracked, replace them. IF they slip on/off of their connectors too easily, they may have stretched out a little bit, cut the ends off, and put them back on.

You may listen for a leak. Sometimes using a cut off piece of garden hose is a good aid to listen with. Sometimes a cardboard tube (like from gift wrapping paper) is helpful. Just remember that whenever you stick your head inside a running engine compartment, that you are not wearing any loose clothing or jewelry that can get caught.

Another suggestion is to use a spray can of carb cleaner and spray around the bottom of the intake manifold, and the base of the throttle body assembly. IF there is a leak, you should hear a change in your engine.
Keep a fire extinguisher handy, or use water instead of carb cleaner (it works, but not as well.) Be aware that if you use water and the wires get wet and it runs worse... your wires may be bad, and the water is allowing them to arc instead of jump the gap of the spark plug.

Another suggestion is: to take a propane torch, turn it on (but don't light it) and move it over the vacuum hoses and connections. The engine RPM's will increase if there is a leak and the propane gets sucked in.

Courtesy of TheOldWizard... Don't forget to remind folks to check the PCV valve, hose and grommet !

oldtimer35 · 02-17-2009, 08:48 AM

The one statement that you make keeps me thinking. When you say you have to screw in the idle screw, how far out is it? The correct setting on almost all ford idle stop screws is to back it off until there is no contact, then bring it up flush with the stop and then one half turn. This isn't to set base idle speed with, like on a carb system, but to limit butterfly contact inside the bore. The idle air control motor sets idle speed, when it is unplugged, the engine should stumble and almost stall, or stall. The idle air control motor should be the only air allowed into the engine, anything else adds to idle speed, so any vaccum leak will bring your idle speed up. When fully open, during cold start, the engine idle speed should be no more than 1800 rpm.
When you unplug the MAF sensor, you send the computor back to the internal settings, sort of a fail-safe system, so it runs off of good known readings.
Check the Idle Air Motor, unplug and see if the engine rpm falls to below idle speed. Make sure the IAC is not stuck wide open, and check for vaccum leaks.
And like BroncoJoe said, check the PCV valve. I have seen these come apart internally and cause the idle to jump up.

RanmaSal · 02-17-2009, 10:01 AM

Quote:

Originally Posted by oldtimer35

The one statement that you make keeps me thinking. When you say you have to screw in the idle screw, how far out is it? The correct setting on almost all ford idle stop screws is to back it off until there is no contact, then bring it up flush with the stop and then one half turn. This isn't to set base idle speed with, like on a carb system, but to limit butterfly contact inside the bore. The idle air control motor sets idle speed, when it is unplugged, the engine should stumble and almost stall, or stall. The idle air control motor should be the only air allowed into the engine, anything else adds to idle speed, so any vaccum leak will bring your idle speed up. When fully open, during cold start, the engine idle speed should be no more than 1800 rpm.
When you unplug the MAF sensor, you send the computor back to the internal settings, sort of a fail-safe system, so it runs off of good known readings.
Check the Idle Air Motor, unplug and see if the engine rpm falls to below idle speed. Make sure the IAC is not stuck wide open, and check for vaccum leaks.
And like BroncoJoe said, check the PCV valve. I have seen these come apart internally and cause the idle to jump up.

You are a well of useful knowledge and an asset to this forum... I was going to suggest the same thing. I've seen alot of IAC's go bad on these trucks.

Also, if you are in a bind and seemingly cannot figure it out and nothing seems to fix it no matter how many parts you shotgun at it... take off the hose that runs to the vacuum booster (brake booster) and plug it. I've had to where the master cylinder was leaking from the back and ruin the diaphram on the inside of the booster and cause a vacuum leak. If that fixes your issue you may have a bad vacuum booster.

What you should do is get a vacuum guage that you can hook up to one of the many vacuum ports on the engine and check vacuum. If it's low, or erratic there is an issue with Vacuum or valves. If it's what the manual says it should be then the issue is not vacuum and you should seriously look at the IAC, or atleast that's what I do... mileage may vary.

Doug Funny · 02-17-2009, 02:06 PM

Thanks to All who posted replies, I tried plugging the line for the brake booster, no change. As for the Idle air motor, I tried uplugging a couple of devices around the throttle body and both had no effect on idle speed (does the idle air motor have a black plastic cap or vent on top?). As for the PCV valve, Is it within a 3/4" vacuum line coming from the bottom of the throttle body? I shook this line and it made a rattle like a PCV valve. I'll try replacing this first. Oh, another piece of the puzzle I forgot to mention, when the MAF sensor is plugged in and idle goes up the exhaust manifold glows. It started to melt my heater box!

Doug Funny · 02-28-2009, 04:28 PM

It was the iac valve. truck runs like a champ. Thanks Everyone!

Doug

Esteban · 07-30-2009, 01:33 PM

I am having the same issue on my 2.3L 4 cylinder engine that I just rebuilt. Idles high then it trys to idle down then it dies. I have seen the exhaust manifold glow when I keep it running. I have done the resistance checks on the IAC valve and it reads 10 Ohms, which is within specs. I have also done the resistance checks on the TPS and it smoothly increases the resistance on the DVM from 0.1 - 3.1 ohms. Is this pointing to a vacuum leak or am I missing something? Also, I have unplugged the MAS when it idles high and it did not affect the RPMs. Any thoughts?

Esteban · 08-03-2009, 10:47 AM

just a quick update. I adjusted the Throttle set screw as mentioned in a previous post and all is well. It purrs now. I remembered before I started the rebuild of my motor that my brother was adjusting the screw. I backed it all the way out, screwed it back in to where it just made contact with the stop and turned it a half turn more. Thanks.