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[Kevin Wood]

Coolant temperature is a possibility. If it's telling the engine ECU it's sub-zero it might result in a rich mixture and elevated idle speed.

Can you reproduce it with your head under the bonnet or is it only when driving?

Don't suppose the EGR valve is leaking air into the system?

Idle air valve sticking open?

Might be worth listening round the induction system, breather pipes, etc. with a length of hose held to you ear. An air leak that big will be audible, IF it's happening at idle with the bonnet up :-/

Kevin

[TheBoy]

Cheers TB but revs are a lot higher than the warmup 1500 or so.  Talking 2 - 3k rev range.  At idle, revving much more than I want it to be...

Silly Q I know, but presumably it actually is revving, and not just an instrument failure?


What about the sticky butterfly suggestion?

[hotel21]

I have another MAF that I can substitute but prefer to not do the standard Fitter option of diagnosis by substitution, if you follow....

[hotel21]

Cheers TB but revs are a lot higher than the warmup 1500 or so.  Talking 2 - 3k rev range.  At idle, revving much more than I want it to be...

Silly Q I know, but presumably it actually is revving, and not just an instrument failure?


What about the sticky butterfly suggestion?

   Its revving mate!!  

Gives the same effect as the cruise failing to disengage!!  

[TheBoy]

Unplug the engine ecu cts (alas plenum off job) - look in TIS, sure there is a substituted value. Also worth measuring and comparing to TIS

[hotel21]

Thanks for the input peeps.  Been head under the bonnet for the past day or two trying to suss out whats wrong and you are pretty much suggesting what I deduced.  

Will confirm free cable in the morning.
Throttle bodies were cleaned at the Lakes meet but will remove and redo, just in case.
Floor mats are secure and not impeding accelerator movement.
Will exchange MAF for substitute.
Had the listening tube out already and nothing heard as regards air leaks....
Will run without air filter for a wee bit to remove potential fault from diagnostic loop!
Been meaning to put a blanking plate in the EGR for a while so good oppertunity to get it done!

Anything else?  

[TheBoy]

Thanks for the input peeps.  Been head under the bonnet for the past day or two trying to suss out whats wrong and you are pretty much suggesting what I deduced.  

Will confirm free cable in the morning.
Throttle bodies were cleaned at the Lakes meet but will remove and redo, just in case.
Floor mats are secure and not impeding accelerator movement.
Will exchange MAF for substitute.
Had the listening tube out already and nothing heard as regards air leaks....
Will run without air filter for a wee bit to remove potential fault from diagnostic loop!
Been meaning to put a blanking plate in the EGR for a while so good oppertunity to get it done!

Anything else?  

Don't buy new sensors without further tests. Most have a substitute value by ecu if failed.  So if you unplug sensor, it will put in sub value - OK, it'll run far from optimum, but should help you pinpoint if it is a sensor.

[Martin_1962]

Sounds like an air leak or a frayed throttle cable

[Auto Addict]

I think it could be the butterfly sticking open, I had the same thing on a Senator I owned once.

[ians]

Not a problem (crack/seal..) with the bagpipes that might have been made worse when you were working on the cambelt?

[Abiton]

Cheers TB but revs are a lot higher than the warmup 1500 or so.  Talking 2 - 3k rev range.  At idle, revving much more than I want it to be...

They will be once the engines warm and 'loose'. The enrichment/IACV control map for the cold start may give silly revs if still present when everything's warmed up, been there, seen that.  I've just cut open a (failed) CTS as  it happens... a little bead thermistor surrounded by silicone heat-transfer compound, inside the brass housing. Thermistor had a chunk blown out of it (I had a short-circuit to injector wiring fault!). I think the usual failure mode is that they go gradually higher-resistance with age, effectively telling the ECU the engine's colder than it really is.  If you google "NTC thermistor failure mode" you may come across the reference where I discovered this. HTH.

Edit: Oops, just replied to the last post on page 1, hope this is still relevant.  

Edit2: Oh, and if it's harder to start than you'd expect when hot, that would be more evidence, I think for this hypothesis. Mine was almost impossible, 'cos the CTS was telling the ECU it was -40°C!

[Marks DTM Calib]

Got to be CTS fault....the revs will be higher if the engine is hot and its on warmup cycle than if it was cold and on warm up cycle.

Do you have a spare CTS, if not I do, Pm me your address and I will chuck it in the post for you.

[hotel21]

Will confirm free cable in the morning.
Throttle bodies were cleaned at the Lakes meet but will remove and redo, just in case.
Floor mats are secure and not impeding accelerator movement.
Will exchange MAF for substitute.
Had the listening tube out already and nothing heard as regards air leaks....
Will run without air filter for a wee bit to remove potential fault from diagnostic loop!
Been meaning to put a blanking plate in the EGR for a while so good oppertunity to get it done!

Cable is free, no obstructions or resistance
TB's cleaned - but were not dirty in the least......
Mats removed - still happens....
Second hand MAF substituted - no difference....
Removal of filter makes no (actual) difference....
Ran out of time for the blanking plate due to other commitments....

Still the CTS fault showing, nothing else.

M_DTM - PM sent

Thanks for the input all.  Appreciated.