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Engine idle

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  #1  
Old 04-04-2018
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Engine idle

When I am driving my 1995 Ford Ranger XLT 4wd, and I am stopped at a light, with my foot on the brake the truck feels like it wants to take off. Then the idle goes down and its ok. Second problem, the engine hmmms than the idle goes real low about to stall than it levels out!!! Does anybody know what this can be, Thank You in advance for your help
 
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Old 04-05-2018
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I assume an automatic transmission?


The idle is set by the computer using the IAC(idle air control) Valve.
IAC Valve is on the upper intake and looks like a "can" laying sideways

First thing would be to clean it: How to: - IAC valve cleaning thread (w/pics) | Ford Explorer and Ford Ranger Forums - Serious Explorations

Good how-to with pictures

Also Clean the MAF sensor, always, every year, dirty MAF sensor can cause all sorts of odd and intermittent issues

Other things it could be:
Speed signal, computer keeps engine RPMs high, 1,100, until speed is under 5MPH
In 1995 speed signal comes from VSS on transmissions tail shaft, this signal also goes to Speedometer and cruise control, and CEL(check engine light) should come on with code P0500 if that was the problem.

TCC, torque converter control, there is a TCC solenoid in the transmission the Locks the torque converter once you are moving and unlocks it when you stop, or engine would stall.
All the transmission solenoids are control by computer Grounding it, they all get 12volts on 1 wire with key on then each solenoid has a separate ground wire back to the computer, if TCC ground wire were chaffed and was getting grounded now and then torque converter could slow down the engine, but again this should cause a code
 
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Old 04-14-2018
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I bought an IAC valve. Pep boys 35.00. I decided to scan the computer with my Innova 3040e scanner. I got a P0402 code, something to do with the EGR valve how do I diagnose this
 
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Old 04-15-2018
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You should post the definition of the code since you already looked it up, I assume.

Trouble codes are good but you need to see what "other" codes the computer has to chose from, they can eliminate things since the computer did NOT choose them
P0400 Exhaust Gas Recirculation Flow Malfunction
P0401 Exhaust Gas Recirculation Flow Insufficient Detected
P0402 Exhaust Gas Recirculation Flow Excessive Detected
P0403 Exhaust Gas Recirculation Circuit Malfunction
P0404 Exhaust Gas Recirculation Circuit Range/Performance
P0405 Exhaust Gas Recirculation Sensor A Circuit Low
P0406 Exhaust Gas Recirculation Sensor A Circuit High
P0407 Exhaust Gas Recirculation Sensor B Circuit Low
P0408 Exhaust Gas Recirculation Sensor B Circuit High

P0402 Exhaust Gas Recirculation Flow Excessive Detected

EGR system in 1995 has 3 parts:
EGR Valve, vacuum operated valve that lets exhaust gases flow into intake manifold

EGR modulator/solenoid, electrically activated vacuum valve, computer uses this to send vacuum to EGR Valve

DPFE sensor, tells computer how much exhaust is flowing into the intake thru the EGR Valve
DPFE = differential pressure feedback
There are two hoses on the EGR Valves tube running to exhaust manifold, one is close to EGR Valve the other farther away, as EGR valve opens the closer hose will have a drop in pressure, more of a drop that the farther away hose.
These two hoses run to the DPFE sensor
The difference in pressure at the DPFE sensor tells computer how much exhaust gas is flowing thru the EGR Valve

So P0402, Exhaust Gas Recirculation Flow Excessive Detected, could only be set by a DPFE sensor reading.
But is the reading correct or is it a false reading?
First I would check the two hoses they have exhaust inside so can get brittle and crack, they also have water inside, all exhaust has water vapor, which is why exhaust systems rust from the inside out.
This water can clog the hoses and after a time clog the DPFE sensor
The hoses are different size so don't reverse them

Next is to test EGR Valve, get a long length of vacuum hose that fits EGR Valve, good to have vacuum hose around in any case, for repairs and for use as a stethoscope.
Pull off the vacuum hose on EGR Valve and put longer hose on the EGR valve
You don't need to plug trucks EGR hose, you are going to test it.

Start engine
Place your finger over trucks EGR Vacuum hose, there should be NO Vacuum, none at all, 0, nada, ZIPPO, lol, so no vacuum present
If there is then EGR Modulator/solenoid is most likely problem, but continue on.

While engine is idling suck on the vacuum hose you put on the EGR Valve, apply a vacuum.
Engine should start to stumble as exhaust starts to come in
Stop sucking and idle should return to smooth idle
Repeat this a few times to make sure EGR Valve is not sticking open, EGR valves do get carbon build up inside and can stick open, so "excessive flow"
If engine doesn't idle well with trucks vacuum line removed then EGR Valve make be partially open, and you will need to pull it off and clean it or replace it.

If everything checks out as OK then replace DPFE sensor on spec, these do fail, from the moisture.
DPFE is working just not correctly, so no easy test for it

These would indicate a DPFE failure or wiring issue
P0403 Exhaust Gas Recirculation Circuit Malfunction
P0404 Exhaust Gas Recirculation Circuit Range/Performance

Which you could test for, but P0402 requires a test of the system and by process of elimination you ID DPFE as most likely problem
 

Last edited by RonD; 04-15-2018 at 10:08 AM.
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  #5  
Old 04-25-2018
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I am looking to buy this DPFE sensor from Amazon for !9.99, it says it replaces original part. DPFE15. Did you here of anybody getting this part, and how it works.
 
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