Ford 2.0L Zetec interesting problem

[DriveHard]

Just looking to get some quick feedback on an interesting issue my daughters car has been having. Patient: 2000 Ford ZX2 2.0L Symptoms: Start cold - starts just fine and goes to high idle As idle slowly drops, it starts to cut out, then try to catch itself. As the idle continues to drop it gets to the point when it cuts out it can't re-catch and dies. Once warm, it starts and idles just fine. If cold and you start it and put it directly in gear, it won't die and idles fine Even when warm, when you put it in gear, it jumps to 1100 rpm...which seems kind of high What I have done: replaced vacuum lines replaced Idle Air control valve What I am thinking: I am wondering if there is a temperature sensor going bad somewhere in that the ECU thinks the engine is warmer than it really is on cold start, so it it trying to cut the idle down too fast, causing the stall. Any thoughts?

 

[Chris142]

Put a scanner on it. See what temp it thinks it is vs actual temp.

 

[InhalingBullets]

just thinking out loud, check out the Mass air flow sensor?

 

[DriveHard]

replaced MAF and O2...still idling like poo and dying. I think it is the throttle position sensor. It reads 17 even when fully closed, and jumps around at idle.

 

[DriveHard]

update for anybody following... replaced the throttle position sensor...problem persists. When sitting at "idle" it is now surging to 2000+ rpm. The throttle position sensor reading is jumping all around from 17 up to the 30's. I am starting to think it is the engine ECU. I can get a junkyard ECU for $35, so probably give that a shot.

 

[JamesBond]

Can you check the voltage at the battery when it's running? The high idle sounds like a vac leak. What hoses did you replace? Try pulling the pcv hose from the intake and taping it off or just covering it with your finger. The tps always shows high on my spi Ford engine even with the throttle closed, but I don't remember it jumping around. Try unplugging the icv and see what it does.

 

[eljefino]

When it's idling grab the engine wiring harness and tug it all around. The potential is there that "any" sensor or faulty wiring is dragging down the regulated (5?) volts, and that the TPS is showing symptoms of this. Not necessarily b/c it's at fault, but b/c it needs the regulated voltage to work well.

 

[DriveHard]

Originally Posted By: eljefino

When it's idling grab the engine wiring harness and tug it all around. The potential is there that "any" sensor or faulty wiring is dragging down the regulated (5?) volts, and that the TPS is showing symptoms of this. Not necessarily b/c it's at fault, but b/c it needs the regulated voltage to work well.

I would think if it was being drug down, it would show as lower throttle position settings...not higher settings. When it fluctuates, it always goes high. I need to find a faster multi meter, so I can monitor the input voltage to that sensor and see if it is going above 5V.

 

[zzyzzx]

What about the PCV valve?

 

[DriveHard]

Originally Posted By: zzyzzx

What about the PCV valve?

I do need to look into that as well...but I am not sure how that would explain the throttle position signal jumping all around.

 

[nthach]

I would say check the ECT sensor but a bum one can and does set a code in the PCM.

 

[DriveHard]

Originally Posted By: nthach

I would say check the ECT sensor but a bum one can and does set a code in the PCM.

there are no codes, and no pending codes

 

[mk378]

Have you looked at the ECT and IAT live data and compare to actual temperature? A sensor can be out of spec and cause runnability problems but not far enough off to throw a code.

 

[mightymousetech]

Did you check the actual throttle plate? Could be loose.

 

[rat]

Originally Posted By: DriveHard

Originally Posted By: zzyzzx

What about the PCV valve?

I do need to look into that as well...but I am not sure how that would explain the throttle position signal jumping all around.

I’ve had a few of these ZX2s. The rubber elbow at the PCV valve erodes and causes a vacuum leak and the very condition that you are experiencing.

 

[meep]

How is fuel pressure regulated in this car? Is it a PWM electronic regulator with variable speed fuel pump? Volvos have that and the fuel pressure senders are known to go bad. vs a vacuum-biased unit. I'd disconnect the evap purge solenoid hose and block it to see if you are getting leaks through the evap circuit.

 

[DriveHard]

I have looked at the live data, and temp sensors seem to match ok with what I would expect I have taken the throttle body off and completely cleaned it out - butterfly is good and tight I need to check the PCV elbow that was mentioned above...I think this might be the winner. I swear I could hear a hissing sound in the front of the engine, but didn't realize there was a possible source of vacuum leak in the front.

 

[DriveHard]

PCV hose and valve were perfectly fine...problem still persists.

 

[DriveHard]

Originally Posted By: meep

How is fuel pressure regulated in this car? Is it a PWM electronic regulator with variable speed fuel pump? Volvos have that and the fuel pressure senders are known to go bad. vs a vacuum-biased unit. I'd disconnect the evap purge solenoid hose and block it to see if you are getting leaks through the evap circuit.

Watching fuel pressure with a scanner real time, it stays pretty rock solid around 40 psi.