1986 IROC-Z28 5.0L TPI.
Hey, ok cars been running sweet untill last wee 'service engine soon' light appeared, so i did a Error Code check and it flashed up 15 (low temp indicated at engine coolant temp sensor) The heater matrix(core) blew 2summers ago and was by passed (dont know if this has anything to do with it)?? Anyhoo, worse i took it a drive and as i get to about 40/50mph in Drive,it hovers between 3rd and 4th with revs at about 3000rpm, it wont settle into a lower gear untill i put it into Overdrive? please help! the gearbox and eng.oil is fine???thanks for looking, Amy x

 

First, fix the coolant temp sensor problem. As it is, the system doesn't know whether or not the engine is up to running temperature, and your computer may not be keeping the air/fuel mix where it wants to be. Bypassing the heater core has no effect on how the engine heats up or performs.

 

thanks what would be the name of the part i need exactly to fix this and ill get it ordered now also can u recommend a gear.box fluid and engine oil for my car as going to give it a change. cheers.