I recently bought a fixer upper jeep from a friend who was rough on it to say the least. Prior to buying it sat for at least 5 years being crancked over maybe once a year. I have done an oil change to include filter, fuel treatment, coolant flush, new brake lines, new brake pads and rotors, and a handful of other minor things. It does run decent now. What has me stumped is the bogging idle. I have yet to actually drive it more than moving it around the driveway/garage so I'm unsure of how deep the problem goes. To summarize its bogging:
-start car idles fine for 5 or so minutes-Starts to drop idle rpm but never enough to kill the engine-when given gas the rpm raises as it should with no delay or bogging -after it returns to idle rpm it starts to bog back down-It comes likes waves where it will idle bad for a minute then back up for a minute on repeat until turned off-While bogging down it sounds like a sucking sound but I cant figure out where it's coming from' On the advice of a friend I replaced the ccv and the pcv along with the lines for both. I'm wondering If it could be the tpc but also have my doubts about the radiator because it looked like the previous guy used stop leak in it. The easiest solution would be that it just needs to be drove and new clean gas put in (wishful thinking lol). Mostly I'm seeking help on what I should do next and if anyone has run across this issue. I am trying to avoid throwing money at multiple options and narrow it down to one.

 

What year? Did you replace the fuel pump yet? If it's anything like the one I have that sat for years, the fuel pump is completely destroyed with the ethanol fuel.

 

The increase in sucking sound is the Idle Air Control (IAC) valve opening up. As for the why... I had a bad experience with old fuel. I would do your best to get the old fuel out of the tank and get new gas in it. I would also put a new fuel filter in before running the new gas into the engine.

 

It is a 1999. I think I will try the fuel pump and go from there. From my understanding this specific year doesn't have a fuel filter. I thought this was odd but I went to both auto zone and oreileys and both said there wasn't a fuel filter for this specific year. When I first ran the jeep after it sitting it was very sporadic on the rpms. It would bog down real low then shoot up real high. I threw a bottle of sea foam in and within a minute it leveled out. It only has a little over a quarter tank of fuel left which I'll try and burn off but I don't want all the sediment that is bound to be at the bottom to run through the system so I figured I would run it just below quarter tank and put some premium in it for the first few fills. I think it's time to bite the bullet and give it a true test drive.