Aloha again! so 2001 Mazda B 3000 5spd 4WD. I thought I had a vacuum leak. well 1 can of brake cleaner and nothing? Next is the IAC ? if I remember it has 5V to it and it does. if I remove the connection after it has warmed up there's no change. its there a way to test it? I even tried to undo the battery for 10min. didn't charge a thing. So just wondering where to go next. It did throw the code P 1506, Motor runs good, just won't idle under 1000 or 12000 rpm. Any ideas? Thanks

 

IAC Valve is a Control not a sensor so has 12volts, like other solenoids do

IAC Valve gets 12volts with key on usually a red wire, other wire is a Ground controlled by the computer
If you were to read IAC Valves voltage with engine running and both Volt meter probes on the two wires while they are hooked up, you should expect to see 7 to 10volts, lower volts = lower RPMs

But do this, after engine is warmed up and idling, unplug the IAC Valve, it should close and RPMs should drop to 500 or engine may even stall either is Good, means IAC Valve was working and no Air Leaks

If RPMs do not drop then could be IAC Valve is stuck open or you DO have air leaks

If RPMs do drop then Computer is holding IAC Valve open(1,200rpms) for some reason, could be faulty ECT sensor(computer thinks engine is cold) or faulty computer

 

OK, I checked the volts at red wire, key on. 12v
Motor warm and unplugged IAC Valve and no change in idle, I think I tested it once with motor running on both + and - wires and it was 6v I dont have my wire probs right now or I'd do it again.
So im thinking its a stuck IAC Valve? I put a lot of brake cleaner even where I know there's vacuum hoses and nothing happened.
if I take it off can I move the plunger in there? I'll try and clean it again.
So any Ideas?

 

I will check the PCV I hear they can stick open?

 

With warm engine idling and IAC Valve unplugged, pull off one vacuum hose at a time and plug that port on the intake, with finger/thumb is fine
Start with power brake booster
Then do PCV Valve hose
Then the smaller hoses on the intake

You want the RPMs to drop lower when port is plugged, RPMs will go up, of course, when you first unhook the hose

Yes, could be stuck IAC valve
Yes, you should be able to move the valve when it has no power,
Its just a solenoid with return spring, when voltage is applied the metal rod(with valve at the end) is pulled back into the solenoid against the spring pressure that holds valve closed
The more voltage that's applied the more the valve is pulled open
The voltage that's use is Learned by the computer and varies from one IAC Valve to another, but within certain parameters, lol
Computers target idle might be 750rpms, so it adjust the voltage to get 750rpms, that might be 6v or 7v, or 6.75v, or 7.5v or....................computer Learns the voltage constantly
Computer has "target" idles from the factory, based on engine temp, transmission and air temp
It adjust the voltage all the time to maintain its target RPM

Now around 1995 or so Emissions got stricter and computers were require to hold idles higher until speedometer was under 5MPH, so thats a different "target" idle in memory
An engine idling under 800rpms has higher emissions that an engine idling at 1,100rpms


Emissions got even stricter so most engines now have to shut down when you stop, no idling at all, called auto stop/start
It does save fuel, but wasn't the reason it as added, lol
The studies do show that if you are stopped longer than 7 seconds with engine off then you are saving fuel, 7 seconds is the break even point for the fuel needed to restart an engine
And totally different starter motor designs for these, so nothing like the starters we have used for years

 

Today I tried all the vacuum lines I could get to. the red and green right behind the intake drivers side I couldn't get to but tested them at the next junction. No change, But I did start the motor with the IAC unplugged and it idled at 700rpm cold motor, until it warmed up then back to 1200. Im going to pull the AIC valve off, If I remember with the AIC off I couldn't move the valve, if so im thinking its stuck.

 

Yes it was stuck, but I screwed it up? after bolting it back the idle went up to 2000 or more sometimes. I ordered a new one. ok 1 week later. I get the new one and get it bolted up, I did pull the negative battery cable for a bit to reset the computer. turn the key and here we go, hum its about the same even after a warm motor, 1200rpm. ok now im thinking yep a vacuum leak. I check all ports coming out of the intake manifold. no change. I couldnt get to the one for the PCV at the manifold but pulled off the valve and put my thumb over the hose. all the same. with warm motor I pulled the clip off the IAC valve, no change.. so doest this mean the computer is doing this? I can kinda live with the idle its not that bad. the only vacuum hose im not 100% sure of is the PCV from the manifold to the valve. I believe it starts close to the thermostat just back under the upper manifold. I have tested it with brake cleaner and nothing? it did finally throw a code I dont have it now but it was for the IAC.

 

Check if throttle plate is closed all the way and not loose, incorrectly installed throttle sensor(TPS) can hold throttle plate open a bit, or throttle cable or cruise cable
After engine is warmed up shut it off
Open throttle all the way and disconnect throttle and cruise cables
Restart engine and see if idle is lower, if so one of the cables is too tight

Remove TPS
Restart engine, see if idle is lower

2001 Ranger may or may not have an anti-diesel screw on the throttle plate rod, on throttle cable side
It looks like an idle screw
Some one may have adjusted it thinking it was an idle screw, its not
turn screw counter clock wise to lower idle

Proper way to set this screw is to warm up engine, and let it idle
Unplug IAC Valves 2 wires
Turn screw counter clockwise until idle is under 600 rpms, engine barely running
Its now set
Plug in IAC valve and RPMs should go up to 750-800rpms

 

I'll check that but there's slack in the throttle cable, no cruz control

 

Hay Ron, I got it!! it was anti- diesel screw. it had a few turns in it. now I'll adjust it, Thanks