Hi there,
My 89 5.3 is running well starts perfectly when cold,slightly rough on tickover,but when i start it when its at temp it starts but is very rough until i rev it a few times then it settles out.
I'm thinking injector couplings/wiring harness
.. all the other ignition components have been replaced..oil pressure perfect..
Any thoughts?
Regards,
Scott

 

The 'could be' list might get a little long.

Injector wiring often causes problems and that's why it is so often replaced.

I'm wondering, though, if you have some drippy injectors. A cold engine would tolerate the extra fuel. A warm engine would object....until the excess fuel is burned off.

Cheers
DD

 

I agree with Doug. A dose of Injector cleaner in the tank, and a good HARD run, may help.

Also, that symptom is classic "gooed" up throttle discs. Remove the air filters, take a solvent soaked rag, and wipe all that Black Goo out of them. Engine OFF obviously.

TPS (Throttle Position Sensor) is out of idle range, age related with them now.

 

That's great I'll have a look at that.
happy New year
Scott

 

89 will be Marelli. If it was Lucas I would put my bet on overheating ignition amp.