S2 revs staying high when changing gear

[Cullystvr]

Hi not found any posts on this so hoping it's not new.
Problem with S2
When stationary revs go up and down as normal.
When driving press the clutch and revs seem to hang at about 2000 rpm then slowly drop (couple of secs) this means is still rerving on gear change so grabs on release of clutch when changing quickly. Ok when you come to a stop at lights as the revs have dropped before you take off
Already changed cable and cleaned linkage and all seems to move freely.
Have tried a spare throttle position sensor but didn't seem to give same throttle response when stationary. Didn't road test as have heard there can be different sensors i.e gold and silver pins, original has silver pins and full ford part number and spare has gold pins and just the ford logo not sure if this is true.
Normally quite good on the S but this has got me baffled.
Any info would be appreciated.

[glenrobbo]

Hi Cully,

I had the same problem on our S ClubTour, last Thursday afternoon after a rather moist drive in the Ardennes.
After disconnecting and spraying WD40 on various electrical plugs, and jiggling the vacuum hoses and breather pipes, the fault cleared and my S3c has behaved impeccably throughout the rest of the trip, including spirited laps of Spa.

I assume it was due to an induction air leak, or water ingress in one of the connectors.

Re the silver vs gold TPS contacts, I believe each type is wired differently. Two of the three wires have to be swapped to regain compatibility iirc.
Don't ask me which ones though!

Good luck!
Glenrobbo

Edited by glenrobbo on Tuesday 23 May 20:10

[Cullystvr]

Thanks for that, did yours only have the symptoms when driving and fine when running stationary.

[phillpot]

glenrobbo said:

Re the silver vs gold TPS contacts, I believe each type is wired differently. Two of the three wires have to be swapped to regain compatibility iirc.
Don't ask me which ones though!

I believe it is the outer two, leave the centre one where it is.

[Cullystvr]

Has anyone swapped them round 😃

[glenrobbo]

Yes, the symptoms last week were increasing revs when depressing clutch to change gear which was 'pushing' me into corners when changing down and making it harder to synchronise engine speed and road speed to engage when changing up.
Coming to a stop and depressing the clutch, the revs would decay, but at a slower rate than normal, settling at about 1200 rpm, still higher than normal idle spwe'd.

I don't think your TPS is the faulty item. Check your vacuum hoses and electrical connector plugs
Also try removing your idle speed control valve and giving it a good clean with carburettor /choke cleaner spray. It can get a bit gunged up and sticky. Likewise your AFMs, but be careful with the delicate vanes when cleaning those.

Edited by glenrobbo on Tuesday 23 May 21:55

[lewdon]

I know you have already cleaned the linkage and cable, but it might be worth looking at the cable again. I had a similar issue when I first got mine. Cleaned the linkage etc and everything seemed fine with it when I tried it under the bonnet, but it still had the fault when driving. Eventually got a friend to work the throttle while I watched what was happening. Turned out the oil in the throttle cable had become really viscous which slowed the movement of the cable on release, the throttle was fine for most of its travel but was taking a second or two to close the last millimeter or so. Running half a can of wd40 through the cable cleared out all sorts of crap and the problem has not happened since.

[Cullystvr]

Thanks for all the info, have to check these out in the next week will update on progress next week.
Any further info would be appreciated.

[Loach1]

I have this problem from time to time on my 2.9 as well, but I haven't really spent much time investigating the cause. I think it MUST be caused by unwanted air, so either it is getting past the butterfly, through the (sticking) idle control valve or just a vacuum leak somewhere between the throttle body and the head (PCV connection?, servo?). Higher revs can only be caused by air, so don't worry about sensors, meters, etc.

Good luck with the troubleshooting. If I find the cause of my problem I will update this thread.

[yknot]

Loach1 said:

I have this problem from time to time on my 2.9 as well, but I haven't really spent much time investigating the cause. I think it MUST be caused by unwanted air, so either it is getting past the butterfly, through the (sticking) idle control valve or just a vacuum leak somewhere between the throttle body and the head (PCV connection?, servo?). Higher revs can only be caused by air, so don't worry about sensors, meters, etc.

Good luck with the troubleshooting. If I find the cause of my problem I will update this thread.

Certainly unwanted air is not ideal but, subject to other factors, such as coolant temp and O2 readings (depending on model) I would definitely look at the ISCV as these symptoms are indicative of this. FWIW when I had a Chim, my ICV looked ok, clean and moved in and out (using Rovergauge) but by changing it for a reliable good one, the idle response was transformed. I concluded that the sensor track within the valve had worn and was sending spurious readings to the ECU which are not easily read using a digital meter and probably only seen on an oscilloscope!!

P

[h271mbk]

I had a similar problem with an efi Lancia many years ago, turned out to be a faulty engine temperature sensor confusing the ecu and causing over fueling. Take out a spark plug, if it's an air leak it'll be running lean I.e. white deposit on the plug, if it's over fueling it'll be sooty.
N

[Cullystvr]

If it's a vacuum leak wouldn't the symptoms be there all the time, the engine runs very smooth all the time, the revs just don't drop quick enough when you change gear. Throttle mechanism and cable are all loose and free. One of the MAFS is very grotty so will clean them and also the idle control valve, once clean will test if still there then have a look at the throttle sensor.
All hoses are good no apparent leaks, servo is holding vacuum which was still there after 2 days when I pulled the hose off it released the vacuum. Could the grotty MAF cause this ? The other is very clean.

[jwigglesworth]

Had something similar which if I recall correctly Matt Smith cured by cleaning the throttle bodies.
HTH

[Loach1]

The point that I was trying to make is that (as far as I know), the ONLY way to increase an engine's RPMs is to let it breathe more air. The only way that should happen at idle is through the idle control valve, so either it is getting stuck or the computer is getting bum info and opening it too wide. The computer also should know the RPMs and from the TPS it should know that the throttle is closed, so it should be trying to close the idle control valve until it reaches a nice tickover. A quick check is to make a blanking gasket out of a piece of card and put it between the idle control valve and the plenum - if the engine still idles high, check the butterfly is closed then look for vacuum leaks. I think AFMs are a red herring because they don't impact the amount of air being let in.

[Cullystvr]

Hi, the original post explained that the tick over is fine, it revs fine and returns immediately to about 1k revs when you release the throttle which is about right, new throttle cable and linkage cleaned, it is when the car is moving there is a problem, when you are driving and press the clutch the revs take time to decrease which causes gear changing problems.
Will be taking off the MAFS to clean, clean throttle pots and butterflies and idle control hopefully will sort it. If not must be wireing 😃

[ukflyboy]

What happens if you disconnect the ISCV? Does it still run once it is up to temperature? If so, are the gear changes more normal? Removing power to the ISCV puts it in the closed position (from what I have read before) so if the problem continues, then it isn't going to be that that it at fault. If the problem rectifies, then maybe it is the ECU getting a false signal that tells the ISCV to energise and let air through??

[h271mbk]

It couldn't be something as simple as clutch drag could it? Pop the rear on axle stands, test it in N then pop it into gear and try simulated driving.
N

[GreenV8S]

h271mbk said:

It couldn't be something as simple as clutch drag could it?

I don't think that's consistent with the symptoms. Clutch drag would stop it engaging the next gear until the revs were matched, and especially make it difficult to get into gear when stationary.

Some engine management systems seem to keep the idle speed control valve open when the vehicle is moving (I think this is to limit the manifold vacuum for emissions purposes) and perhaps there's something like this going in here.

[Loach1]

As far as I know, the ECU has no idea that the car is moving, so there can only be one setting for the RPMs when the throttle is off. The fact that it is higher when driving still can only mean that there is air being admitted into the engine that doesn't occur while sitting. MAFs do not let in air, the TPS does tell the ECU that you are off the throttle pedal, but that should be consistent moving/not moving. Have you unplugged the ICV to see if the engine dies? If it does, it's obviously doing something. Take it for a drive unplugged to see if it resolves the issue. If it still hangs between shifts then you have a vacuum leak that shows up only when moving.

[mentall]

According to the V6 diagrams in Heath's book, the Vehicle Speed Sensor on the gearbox (VSS), as well as controlling the electronic speedo, feeds pin 4 of the ECU (through a yellow/brown wire). It's a magnetic sensor, outputting a square waveform.

Probst's book says this controls Cruise Control, converter lockup and engine cooling fan: none of these are implemented on our cars. But it also controls idle-air bypass (ISCV): it tells the ECU to stop fuelling, and close the ISCV to give maximum engine braking on deceleration; then to reopen the ISCV before the car reaches standstill to give a smooth transition to idle. I believe this function may well be implemented on our cars (in theory, and if it works!).

I now look at my S3C and find NOTHING connected to ECU pin 4, but a yellow/brown wire to pin 3. The Sierra XR4x4 engine wiring diagram which otherwise corresponds exactly with my car agrees there should be a yellow/brown on 4 (and nothing on 3), but doesn't tell me where it goes (it vanishes into the body wiring diagram that I haven't got!). Something else to investigate.

I still can't say what WORKS, as I can't get the damn thing to run properly at all.

But I suspect that the ECU DOES know the car's moving, and how fast.

Incidentally, Probst says that the cooling fan control cuts out the fan entirely at 45mph: not a bad idea, if we could make it work?