I'm thinking about buying a 99 Dakota 4x4 that has the 5.2 or 5.3 V8. The truck only has 77,xxx miles on it. I test drove it today and it runs like a champ. I only drove it roughly 10 miles but it done real good. After I finished driving it I took it back and shut it off. I started it again approx 15 mins later. I let it idle for 5-10 mins then it started idling fairly rough. The rpms dropped down to around 500 and it almost sounded like it was about to die. I turned the AC off (it was on max AC at the time the rpm's dropped) but it didn't seem to help. It acted this way for approx a minute than began to idle fine. I turned it off and started it back up again but no luck getting it to do it a 2nd time. The previous owner said he noticed it would do it the worst on cold starts but says it normally begins to idle fine after a minute or so with no other problems. The check engine light never came on and I made sure the bulb still worked lol. Only after market parts is the exhaust tips but its only a cat back exhaust. Previous owner said he changed the plugs and wires about 20,xxx miles ago. Any suggestions on what this may be? Any help would be greatly appreciated considering I'm supposed to buy it tomorrow depending on how severe this problem may be.

 

Also forgot to mention that I looked at the gauges and they all appeared to be in the proper zones. It wasn't over heating. I looked at the engine and didn't see any fluid on or around it. Nothing leaking out under the truck either. Just thought I'd mention that in case it helped.

 

Would be a 5.2L or 5.9L. 5.3L are chevy. But to address your concern here:
Ask him if he canged the cap/rotor as well with the plugs and wires. Also ask him what kind/ brand he used for wires, plugs, cap, rotor.
Next I would ask him to remove the air hat from the top of the throttle body, then (with the engine off!) open the butterfly valves and look down into the intake with a flash light in one hole. If you see any black/brown then you have a bad plenium gasket(very common for dodges). Could be why it has a rough idle.
Besides that I would check the normal stuff, condition of the air filter, color of oil, etc.
Report back and post picks if you buy it!

 

Well I ended up buying it. I didn't ask him any of those questions because I didn't read your post until now lol. But yeah I've heard about the gasket leaking on these dodges and that might very well be the problem. Just to clarify it is the 5.2 318 engine. I did crawl under it and noticed it had an oil leak. You couldn't tell it from looking at the motor from the top so could it be leaking from the plenium gasket? I'm unfamiliar with dodge so I have no idea where the gasket is even at. Other than the occasional rough idle it drives really well considering its age. I'll post pics ASAP!