Rev4 takes 10 mins to warm up with rich fueling, bad mpg

[DaveImok]

My rev4 engine appears to take a long time warm up under load, it runs rich from start up until it reaches normal temp which is mid way on the guage.
The probem I have compared with the rev2 is that I use it a lot for local shop trips from cold & the idle or rich mixture does not settle down until I get back home so my fuel consumption is very high on short trips.

Is the Cold Start Injector Timer Switch meant to cut the rich fuel mixture before the coolant temp sensor or thermostat?
Can anyone help explain the timings here?
Are there any tricks to stop the choke or rich mixture sooner so that it still starts?

[toxo]

You probably need a new thermostat. When you say 10 minutes, is that how long it takes the temperature gauge on the dash to reach operating temperature? That should be around 2-3 minutes, if it's taking 10 your thermostat is weak and is opening too early. If the temperature gauge reaches operating temperature in 2-3 minutes but you think the car is staying on a 'cold map' for far longer, you probably need to change your ECU coolant temperature sensor.

There is no choke, the entire thing is controlled by the ECU altering timing and fuel maps until such time as it sees that the coolant is warmed up. I'm pretty sure that the rev4 doesn't have a separate cold start system (older engines have a cold start switch which triggers a 5th fuel injector very briefly during startup).

Is the car a turbo or n/a?

[DaveImok]

It a 1997 uk rev 4 normally asperated.
yes its taking 8-10 mins to get up to temp.
sounds like it needs a new thermostat, if I can find where it is
Cheers for the info.

[toxo]

Open the engine lid, look in from the driver's side. Next to the dipstick is a thick coolant hose. Where that meets the engine is where the thermostat is. 2x10mm bolts, one is a bit of a pain because it's underneath.

[DaveImok]

Hi I changed the thermostat but its still running rich and now failed the mot emissions test

I guess the next thing to try is the 2 wire coolant ecu sensor but where is it?
Do I need to get at it with car ramps from underneath, will just disconnecting it prove it before replacement?
Any help is much appreciated.