I have a 1998.5 5.9 24 valve dodge 2500 diesel. Recently had the transfer pump replaced then right after it started having a bad/missing idle in park but only when truck is warmed up. I replaced O rings between transfer pump and oil filter housing, changed fuel filter and cleaned air filter. Any suggestions on the bad idle?

Ok what kind of fuel pressure do you have? (Idle and WOT at highway speed)Do you have any hard starting issues in the morning?Any error codes present by chance?

I don't have the tools to check fuel pressure and I did have issues with starting in the morning before the transfer pump was replaced but now it starts easy. There is no codes

Might be a mild air leak from the lift pump change. You could air some pressure to the fuel tank and have a second personal crawl around under the truck looking for damp spots. It might be dirty injectors... http://articles.mopar1973man.com/2nd-generation-24v-dodge-cummins/25-fuel-system/62-injector-cleaning

r u saying put a compressor on the lines at the transfer pump pushing air towards the tank to look for a leak?

No, pressurize the tank at the fill up door. Then crawl underneath and follow the lines from the tank to the VP and look for wet spots. If you have a wet spot then that would also be where there is an air leak.

How many miles on the injectors? One could be sticking

I put about 100k on this truck since i have had it and haven't did anything with the injectors if I pull them how do I tell if I have a sticking one or a faulty one

You will have to remove the nozzle and see if the pintle slides good. With over 100k, a new set wouldnt be a bad idea.

You will have to remove the nozzle and see if the pintle slides good. With over 100k, a new set wouldnt be a bad idea.

Wouldn't be a bad idea to sit down with a digital caliper and measure all the parts and see how tight/loose they are. Like my little cheapy calipers do measure down to 1/10 of a thousandth.

Rough idle is often due to air bubbles in the fuel on the suction side of the lift pump. First Gens were easy to diagnose by putting very temporary clear plastic PCV tubing on the return line. Should not have bubbles. Best location is after the drain T for the injectors. 2nd Gen and later requires creativity to fit tubing.

I would like to start by saying thanks to everyone who gave me suggestions. I ended pulling the injectors and found a shop that would pop test them for free, they weren't up to standard so I had them rebuilt and my problem was solved. Moparman I will be in contact to help the cause when I am able very soon

Wow! Free pop testing, thats great!