Will Faulty VSS sensor cause revs to idle high then low when vehicle s

[demented]

I've replaced MAF sensor and ISCV from donor 1.8 Escort, one that's running spot on.

Also, briefly disconnected the O2 sensor.

 

Yet, I still have eratic idle, now when stationary and also when coming to a stop.

 

So, will a faulty VSS cause such an issue, especially when stationary and engine idling.

 

Will disconnecting a faulty VSS actually make a difference ?

Once disconnected, would the ECU just detect there's a fault and have no effect ?

 

Also, when PCV valve pipe at the rear of the engine is disconnected and the inlet manifold pipe blocked, covered by my finger, should the engine stall ?

 

 

I find it hard to understand that two engines, the Rs2000 I4 and the Zetec, although inherently different, suffer from the very same issue, such that appears totally impossible to rectify.

[scottg17]

Did you ensure that the MAF has the same code stamped on it as yours, 1.8 zetecs were run on many different ECUs so youd need to get a matching MAF sensor

[demented]

No, I didn't and I wasn't aware of that.

 

But the donor car runs perfectly with the swapped MAF sensor.

 

And the MAF sensor from the donor car, same issues occurred when fitted.

 

So, I came to the conclusion that the MAF sensors are not at fault, on the understanding, that swapping a known working one made no difference and a suspected faulty one, didn't cause the same effect when fitted to the donor car...?

[opexo]

VSS doesn't affect the work of the engine when stationary. Only when the car is moving. If it's faulty the car may stall when slowing down.

[demented]

Thanks.

 

No, it's not stalling when stopping.

 

I've partially disconnected the pipe from PCV valve and although still revving high, its not revving as high or as erratic.

 

Also, with PCV valve reconnected, when I unplug ISCV electrical connection, engine will idle, so I'm suspected issue could be PCV Vale related.

[Georgio]

I would also suspect TPS...they can do weird things to fueling and run the engine like crap...If you have a known good condition one,try it,although most sh ones are knackered and send the ecu that you press the accelerator when you are not.You can try to disconnect it and try for some miles,but the engine will run like crap,it won't accelerate when you want it and have a huge flat spot....I had overreving problems and some times stalling,but most of the times it was revving.Other engine,I know,but similar symptoms

[demented]

I have another 1.8 Escort which is running spot on, never had engine problem with it, only a replacement gearbox.

 

So, can swap engine parts off that.

 

Tomorrow, I'll swap TPS and try the PCV valve and rubber pipe etc, see what result I get from that.

 

Thanks.

[demented]

Swapped TPS and PCV valve rubber pipe and no difference.

 

Even fitted suspected faulty parts to the good engine and it ran spot on.

 

Struggling with PCV valve at moment, I know where it's located but unless it's buried in its metal surround, I can't see it to remove and swap.

 

Although I've replace the gearbox, I can't remember whether the VSS, once the speedo cable removed, just unscrews from the gearbox.... any ideas ?

[demented]

If anyone is interested, I've found the PCV Valve.

 

Didn't realise it was so small, It was still stuck in the end of the rubber elbow pipe when removed.

 

I'm hoping a faulty PCV valve is the cause of this idle issue.

[nzesky]

I know it's been a while but did you ever manage to get this sorted? I'm having similar issues with mine and it's a nightmare to try and track it down.

[demented]

 

Yeah, I believe on this occassion it was a faulty PCV valve.

 

The PCV valves should be replaced periodically during servicing, yet is often not.

 

I believe the faulty PCV valve caused either too much or too little air to enter the manifold and the ISCV was attempting to compensate.

 

To help identify the issue, while engine idling with revs rising & falling, locate the pipe from PCV valve and without removing or disconnecting anything, squeeze the rubber pipe from PCV valve with long nose pliers and attempt to control the idle, if you can, this eliminates a ISCV issue and in my opinion, points to a faulty PCV valve.