[chartmaker]

Hello,

I have 2004 Ford Taurus with high idle issue. I did a live data scan with my OBD2 tool and the RPMs during cold start is approx. 1450 and when driving or at operating temp, it stays around 925. Also, when the AC/heat is on, the RPM drops to around 750 to 800.

There are no check engine light/codes. I sprayed brake cleaner around all the hoses/vacuum lines and it didn't make any difference. I swapped the throttle body & MAF sensors and it didn't resolve the issue. Also, the fuel pressure fluctuates between 39.5 to 41.5, so could it be a bad fuel pressure sensor, faulty fuel injector(s) or the manifold runner control o-ring?

Thanks in advance.

Very normal fuel pressure. Check fuel trims. I had '04 leaking around the EGR gasket but not enough to set a code. ~=15-20% at warm idle. Made for high idle and less than happy when cold.
Wrong gasket on the EGR to intake. Small leak.
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[chartmaker]

Thanks. I will check the EGR gasket area and the o-ring going into the intake.

It leaks or not, best check fuel trims at warm idle and let it tell you if you have an issue. Pic of mine after fix.
Any thing +/-10% not an issue. Best not trying to fix things not broken. I had bad data, traced it to this, first time in all my 11 Bulls had this. Lots of things can cause vacuum leaks, but first test to see if you have an leak. If not move on, it it is leaking, then find out where.
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[chartmaker]

Okay, thanks.

Just for discussion. Engine rpm/power is managed by air flow. Throttle manages air flow, and IAC manages air flow, and PCV manages air flow. Then leaks add air.
The PCM adds fuel to math that air as measured by the MAF. If idle is too high and trims are in line, then one of the managed air flows is high. The PCM is making it high.
I know from experience, it you open up the throttle plate screw idle stop, it will not make the idle go up. PCM just adjusts for that. Things that make the PCM add more idle. PS pressure switch, and A/C clutch relay. Both to correct added load. If the A/C clutch it called for and it does not engage or no load is experienced when it does, idle jumps up and is not matched by load.
From experience: PCV stuck closed/ or wrong size for the car and idle will be low or high and the PCM will not try to correct. Had cheap Autozone PCV and car would drive 30 mph on level ground.
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[chartmaker]

Thanks. So, if I have it on Drive, it would easily drive up to 20 miles on level ground and I don't need to put my foot on the pedal.

I didn't see any leaks by the PCV elbow or line, but will clean or swap the PCV if required.

Only MC PCV is acceptable. Aftermarket is not like OE.
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[chartmaker]

I couldn't find the IAC percentage/duty cycle with my scan tool, but noticed the TPS% at 17.2. Also, when applying brakes during cold starts, the RPM drops a little but no issues at operating temperature. Could it be from the vacuum pressure building up at cold start?
View attachment 222122

At idle stop, TPS % should repeat. Move throttle and let it settle. Non repeat will cause bad idle. Pic of data from my TPS. I replaced the TPS and made NO difference. Still not repeating. Back probe the signal and it is unstable when idling. Key on but not running solid stable. When idling, the "return" line is unstable. It is GROUND to the PCM ground. Traced issue to PCM ground at firewall. Bad ground caused PCM to get bad ground and sensors bad signal = not body ground.
When you start, the PCM reads your TPS as idle. In the bad case you press the throttle to start, PCM uses last true idle stop start. That ground is basic maintenance. Ford bolts the grounds over paint. OK when new but it goes down hill with age. Fix easy. As you might guess, I was going working to find bad idle.
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[chartmaker]

Didn't read everything in detail so this may have been already addressed but is the throttle plate sticking open ever so little. Either physical damage or crud can cause this. Also look at the cruise control cable connection to the throttle linkage. I believe 100% of idle air flows through the IAC valve, at least on the Vulcan engine.

Idle air flow is constant through the PCV. At idle only it is constant as the vacuum holds the plunger to a fixed opening. If all is in good shape hoses and gaskets, that air is "metered". Air that is metered flows to the engine valve cover and all that comes back to the intake. The PCM has the reading of mass flow air, and 99% of that should reach the engine with no significant leaks. If IAC flow is excessive as an example, the PCM knows about this but will not try to fix it. Leaks in the air flow MAF hoses to the engine will result in high fuel trims. High flow or low flow through the PCV are known by the PCM and will not result in high trims. High trims results in when "un metered" air gets into the intake.
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[chartmaker]

The EGR valve can leak in 3 ways.
Suck on the small tube with a bit of hose and the diaphragm should hold the vacuum. Leaking will not effect running. At idle there should be no vacuum on the line from the solenoid.
The exhaust path can leak and let exhaust into the intake at idle and make for rough idle but should not mess with fuel trims.
Air can leak in through those vent holes through the shaft seal and let air into the intake. That would lead to higher fuel trims at idle.

So a exhaust leak through will make for bad idle, slow idle. A leak of air though the haft will make for high fuel trims at idle and may make high idle.
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[chartmaker]

OBD-II Monitor Exercised Drive Cycle Procedure
Drive Cycle Preparation overnight resting before starting.
1. Idle vehicle for 15 seconds.
2 Drive at (40 MPH) until ECT is at least (170 F). .
3. Is Inlet Air Temp within (40 to 100 F)? If not stop here.
HEGO
4. Cruise at (40 MPH) for Up To 4 minutes. Executes the HEGO monitor.
EVAP
5 Cruise at (45 to 65 MPH) for 10 minutes (avoid sharp turns and hills) Gas tank ¼ to ¾ full.
Catalyst
6. Drive in stop and go traffic conditions. Include five different constant cruise speeds, ranging from (25 to 45 MPH) over a 10 minute period. Executes the Catalyst Monitor.

EGR
7. From a stop, accelerate to (45 MPH) at ½ to ¾ throttle. Repeat 3 times. Executes the EGR Monitor.

SEC AIR/CCM
(Engine)
8. Bring the vehicle to a stop. Idle with transmission in drive for 2 minutes. Executes the ISC portion of the CCM.

CCM (Trans Auto)
9. From a stop and in overdrive, moderately accelerate to (50 MPH) and cruise for at least 15 seconds. Stop vehicle and repeat without overdrive to (40 MPH) cruising for at least 30 seconds. While at (40 MPH), activate overdrive and accelerate to (50 MPH) and cruise for at least 15 seconds. Stop for at least 20 seconds and repeat step 9 five times. Executes the transmission portion of the CCM.

Misfire&Fuel Monitors
10. From a stop, accelerate to (65 MPH). Decelerate at closed throttle until (40 MPH) (no brakes). Repeat this 3 times. Allows learning for the misfire monitor.
This a summary of Ford drive cycle.
I have had several reset of PCM due to battery install, battery cable and such All except EVAP reset in normal driving is a short time.
EVAP requires gas tank at level noted and outside air temp as noted.
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