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kohlbeezy

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hello yall. hopefully someone out there can help me out. I am currently trying to get my 85 ranger smoged. it has a 91 4.0 and manual trans out of an explorer. i am currently getting a code 41 (lean engine condition) so therefore it cannot pass smog. (damn california). it passes the emissions test with flying colors. i have read that it could be the fuel pressure regulator and or the O2 sensor or neither and someting completely different. I am thinking of just replacing the two parts and go from there. im sure they are the originals so it is probably not gonna hurt my situation.

also, it seems to idle high. around 1000 RPM. when coming to a stop at a light or stop sign, with clutch depressed or in neautral, it seems to idle around 1200-1500 RPM. this is continues or about 10-20 seconds after i have come to a complete stop, then the idle drops back down to around 1000 RPM. I have researched the neutral sensing switch that is located on the passenger side of the trans top cover. could this be the source of the high idle. i guess it regulates the idle in neutral vs in gear. not sure why that matters in a manual.

any and all help is appreciated. thanks guys.
 


RonD

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Manual trans doesn't have a neutral switch or sensor.
It has a clutch pedal switch that must be closed for starter to work, clutch pedal to the floor closes the switch.

Idle on fuel injected engines is control by air, specifically the IAC(idle air control) Valve located on the upper intake by the throttle plate.
This valve sits on an air passage that by-passes the throttle plate, it uses a Stepper Motor, computer can set idle by opening and closing this valve sending specific voltage pulses to the motor.
IAC valves can get dirty and stick, might be worth a look with cleaning in mind.

Target cold engine idle is 1,100 to 1,200 depending on outside temp.
Warm engine idle is 700 for manual, 800 for automatic.

Since you have a higher idle and also getting a Lean code I would suspect a vacuum leak.

Replacing O2 sensor is fine but that won't be the problem, it is like shooting the messenger, lol.
O2 sensor is working because you are getting the Lean code, it's not usually the other way around.

4.0l are know for loosening lower intake bolts, check them.
MAF sensors are also the source of Lean code, clean it, and make sure the air tube from MAF to intake is air tight, a leak in this tube is a vacuum leak, but wouldn't produce the higher idle.

To check for vacuum leak warm up engine, with engine idling unplug wires on IAC Valve, valve will close all the way, idle should drop to 500 or engine may even stall, if that happens then no vacuum leak.
If idle stays high remove vacuum hoses, one at a time, from intake and plug port with finger, if idle drops that hose or it's device is leaking.
You can also spray carb cleaner around intake listening for a change in RPM, but be careful around hot exhaust.
 

kohlbeezy

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Thanks for the good info but early Mazda transmissions DO have a neutral SENSING switch. It is the sensor on the passenger side of the top plate. This has nothing to do with the starting of the engine. I think it has to do with telling the computer the engine is in neutral for idle control and also to tell the transfer case control module the Trans is in neutral to allow 4 lo
 

RonD

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Last edited:

kohlbeezy

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Awesome. Thank you
 

adsm08

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The proper fix for your issue is to move out of California.

The over all description sounds to me like a vacuum leak. I'd start there.
 

Mickey Bitsko

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My credo
live everyday like your gonna die tomorrow
Register it in Plumas County , no smog check there...
 

kohlbeezy

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ok so here is an update. when i got home i disconnected removed the IAC valve and tried cleaning it. i think i just need a new one. there was A LOT of carbon build up. when i reinstalled it and disconnected the connector while running, it did not drop in idle. however, with it disconnected the rpms did drop more rapidly when blipping the throttle. instead of stopping at 1200-1500 rpm, it went straight down to 1000 rpm. while running, i disconnected each of the two (excluding the break booster) vacuum lines and plugged the port with my finger, no change in rpm. i then sprayed break cleaner on the lines, no change in rpm.

i also tried cleaning the MAF sensor. when removing it, i noticed a lot of white stuff. cleaned it with alcohol and reinstalled it. no change. i hate just throwing parts at things to try and solve the problem. thinking i may get a new MAF and IAC instead of o2 sensor and fuel pressure regulator.

is there any way to test the MAF?
 

kohlbeezy

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So I replaced the IAC and MAF. Still had the check engine light come on. I tried using a code reader to pull the code but nothing happened. Any other ideas or possibilities?
 

RonD

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Did you disconnect the battery while swapping sensors, you should.

This does two things, first it prevents shorts from damaging electrics, second it will cause computer to reboot when powered up again, this will cause computer to look for and "relearn" sensor voltages.

The fact you can't "talk" to computer needs to be addressed first, if computer has problems nothing you do externally will help, so make that connection work.
 

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