XF GHIA EFI idling high in neutral when hot

[xr6tjet 98]

Hi guys,

 

Have a problem with my XF efi where the idle goes to almost 2k RPM in neutral when the car is at optimum temperature. When I return back into the gear the idle sits below 1k rpm. I have changed the AFM to another stock one, same thing. Changed the ISC to a spare one, same thing. Tried fiddling with the idle screw and air flow meter adjustment and still same thing. I have no idea where the problem is. Can anybody please help me !! Could it be timing that could be off? The car idles and drives lovely.

[xr6tjet 98]

I have also driven home without the ISC connected and it still idles high at around 1800rpm (almost the same)

[ZL. 19]

check your coolant sensor it should read something like(resistance) 5ohms when cold and 20ish when at temp, roughly ill have a look for the actual figures

[xr6tjet 98]

Where abouts is the coolant sensor? I know where the coolant level one is but where is the one you speak of? cheers

[gerg 10,871]

It could also be a vacuum leak. These are notorious for it. Stuck throttle plate? It's obviously getting air from somewhere. If it was coolant temp sensor, then the computer would be opening the ISC valve so disconnecting it would drop the rpm.

[ZL. 19]

coolant sensor is in the head where your heater hose is, coolant sensor controls mixtures mostly, could be a vac leak but wouldnt be intermittant would be constant but more noticable at revs.

[xr6tjet 98]

Another thing: When I rev the car the idle sits and doesn't drop rapidly like a normal car does when the car is warm. I have no idea where the leak could be. When we rebuilt the top half of the motor we made sure all the vacume hoses go where they're suppose to via factory schematics and they are all hooked up. When i remove the oil cap the car seems to stall no problem.

[xr6tjet 98]

I also noticed that when I'm driving it seems to drive on its own (only when warm)... like its holding the rpm and the speed until I start braking and slowing down. Will check coolant sensor tonight

[SPArKy_Dave 8,890]

Check the throttle body, for a sticky butterfly.

When it's idling high, open the bonnet, and make sure the throttle butterfly is fully closed.

It could be expanding and sticking slighty, when hot.

 

If not the butterfly, and not ISC related, try looking at the EGR valve for a leak,

and maybe look to see if the timing is varying.

[xr6tjet 98]

How can I tell if the butterfly is sticking? By looking at where the throttle cable connection area?

[xr6tjet 98]

Disconnected the tps sensor and the problem still happens exactly the same? Idle did not change at all. Could it be faulty?

[xr6tjet 98]

Disconnected the green plug spout for timing. Idle went down to normal. What could the problem be?

[Mr Polson 10,214]

Dizzy or ECU I think. That's what was suggested to me when I was having issues, if unplugging the spout connector DIDNT change anything, it would've ruled out ECU and dizzy.

 

So in your case maybe it means its ECU or dizzy related.

 

In saying that, I think it could still be something that provides the ECU with an input.

[xr6tjet 98]

Could it be that my base timing is off and given my harmonic balancer is wobbly under 1k rpm could that also change it? Could it be my slightly larger cam? Im stumped cos it only does it once its hot. If i turn the car off while it revs out and turn it on again the idle is fine. I have an entire head with everything on it which i have started to swap parts to mine. Changed tps today and it didnt change a thing.

[ZL. 19]

have a look at the relays for the fuel pump and ecu, someone put a 4 pin relay in the 5 pin ecu relays place in my fairlane befor i bought it, and it made it do heaps of wierd stuff, and was a prick to find. also get a long screwdriver and put one end on each injector at a time the othe end on your ear and listen if any of the injectors sound irregular. was the tps you swapped a good one?

[xr6tjet 98]

TPS I put on the car was off a low mileage head I recently purchased. I have a few more things which I will swap over to test out on my car to see where the problem lays

[Mr Polson 10,214]

Have you done a self diagnostic test?

Use a led test light and short out a connector...

 

I'll look it up more specifically if you're interested.

[xr6tjet 98]

No I havent I know you can do it but I can't seem to find a guide. If you know how please let me know that would be appreciated!

[xr6tjet 98]

Found this - can anybody confirm its the right procedure for testing?

 

The XF has a diagnostic mode, access this and post the results.

To access the codes:
-Find the diagnostic connectors (near the brake booster).
-Jump the white/red wire on the self test connector (single plug) to the black/white wire on the diagnostic connector (3 terminal plug).
-Connect an LED test lamp between battery positive and the brown/red wire on the diagnosic port.
-Switch the ignition to ON.
-The 'fast codes' will be displayed first, ignore these. (the light will flicker)
-The next codes are the 'hard codes', record these.
-After a 6 second pause, the memory codes will be displayed, record these.
-If you need to repeat the codes, turn the ignition off for 15 seconds and then back on.

Each set comprises of a series of 0.5 second pulses, a 2 second pause and a further 0.5 second set of pulses. The first set represents tens, the second set represents units.
If there is more than one code in a group, they will be seperated by a 4 second gap.

Ie. for code 12, you will get one pulse, 2 second gap, then 2 pulses.

Codes
10. Seperator code
20. Engine identification
11. System pass
12. RPM out of spec.
13. RPM out of spec.
15. ROM test failed (ECU memory)
21. Emgine coolant temperature out of range
23. Throttle position signalout of range
24. Air temperature signal out of range
26. Air flow sensor signal out of range
34. EGR not flowing
67. Neutral drive signal or air conditioner on (engine off)

According to the book, the problem could be one or more of the following:
TFI system
Fuel Supply
Air flow meter
Coolant temp sensor
Idle speed control valve
Throttle position sensor
Control relay
 

[Mr Polson 10,214]

Yep that's right.

[xr6tjet 98]

Found the bloody problem. After examining my spare motor i found the throttle much tighter then mine. I examined my motor and i have no return spring on my throttle. Explains the sticky idle. Thanks for the help guys i will fit the spring this weekend.

[gerg 10,871]

Well fuck my horse.

[xr6tjet 98]

I know right. So simple... the egr valve on low mileage spare motor may aswell go on too it looks better then mine lol