I have a 1991 camaro z28 305 tpi

when the car is cold, so the morning for example, it cranks for 3 or 4 seconds before starting. also I have noticed it idles straight away at 750rpm, while normally when its cold it will idle higher at between 1,000 and 1,200 until it warms up. So I am pretty sure a sensor has gone, but I have no idea which one, where it is, how easy it is to replace and where I can get one from.

Any ideas would be great!

Thanks

 

Check your coolant temp sensor. The one the ECM uses.
Somebody correct me if i'm wrong but I believe it's the one on the front of the manifold.

There's a temperature vs resistance table somewhere on this site. At a true cold start you should measure the value for ambient temperature.

 

Thanks for your help

If it is that sensor, would my fan still turn on? As far as I can tell, once the car is running the temperature acts completely as normal, so the thermostat is kicking in properly and the fan turns on when it get up high enough.

 

your fan could be being kicked on by the auxiliary fan switch, its basically a back up

 

Completely different sensors.
You have 1 for the ECM, 1 for the gauge, and 1 for the secondary fan.

 

Ok, so using my fantastic powers of deduction, if my gauge is working, and my fan is working, the ECM sensor must be the one needing attention?

 

It needs attention in the form of a checkup.
Ohm that bad boy and see if it lies to you.
If it's lying to you then it's lying to the ECM as well.