Nissan Repair: Rough running during fast idle

Question
QUESTION: I have a 1986.5 Nissan 4x4 hardbody pickup. V6 manual transmission that misses while running in the fast idle mode. As soon has it idles down it runs smoother. New plugs and spark plug wires have been placed. Usually happens when cold in morning but not as much if it has been sitting during the day and it is very hot outside. Gas mileage has been decreased lately also. I am running regular non-alcohol fuel and have tried additives to clean the injectors. Pleas let me know if you have any ideas to solve this issue!

ANSWER: Hi Floyd -

Can you tell me if the check engine light is on?
If so, I will need the OBD code and we can start from there.

If not, then I would check the fuel pump. Have both the volume and pressure checked.

Hope this helps -
aloha
Calvin

---------- FOLLOW-UP ----------

QUESTION: The check engine light is NOT on. Will check the fuel pump. If this is not it, are there any other things to check? fuel preesure regulator? faulty fuel injector? O2 sensor? Idle air control motor?

Answer
Hi Floyd -

If there is no check engine light, then it cannot be IAC, O2, or fuel injector, as it would trigger a code. That is why I asked if there was a light. However remotely possibly the regulator, but that rarely gives out.

Only 2 components is not on the OBD system that illuminates the check engine light. That would be the fuel pump, and the ignition module located in the distributor.

Hope this helps -
aloha
Calvin