How to solve idle and acceleration problem on my cherokee sport 99

Hi, i have a 1999 cherokee spoort straight 6 4.0L standard gear and about a year ago i started having some issues with it. when i turn it on seems to work pretty fine, but after a few minutes the idle goes down, and when i push the gas pedal it wont accelerate, it feels like no air can go into the motor; after trying hard with the gas pedal suddenly accelerates, but after i take my foot of the gas pedal it falls again. when that happens i turn off the engine, wait for about 30 seconds and start it, that gives me a few minutes, and then again the problem. I`ve already done a tune up, check the gas filter and clean a micronic filter that is inside the fuel tank; cleaned the injectors, the distributor cap, changed spark plugs and cables. the last mechanic told me it was the TPS so i replaced it and it worked fine for like a month, and after that, again the problem. The last thing i did was to clean the IAC valve (About two months ago) and after that it worked better than ever!!! (the motor power, performance, etc) but yesterday it started giving me the same problem again. I took off the IAC valve to clean it again, but the problem just got worse, because now there are times when it just doesn´t accelerates enough to move (maybe i messed it up). Now i am thinking about replacing the IAC valve, but i would like to know if there´s anything else that would be causing the problem (the fuel pump seems to be working fine and there are no vacuum leaks). Thank you very much for your help!!!!!

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Have you checked the fuel pressure with a mechanical gauge to verify operation?

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thank you Pat for your help. No, i haven´t checked the fuel pressure with a mechanical gauge, but when i removed the fuel tank to clean the filters, i sent the fuel pump for a check up and they said it was working fine (i forgot to mention it). Do you think the fuel pump could be giving me this problem? again thank you very much for your time and help.

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Good news!!!!! i was thinking to change the IAC valve, but the guys at the parts store told me they didn´t have it right now, so i have to wait until tomorrow, i thought meanwhile i can keep on looking here in IFIXIT for more tips, and i found a person that owns the same model as mine and was having similar issues with his truck, and a person was saying that he should check his vacuum lines, in fact he was pretty shure the problem was in there. So i decided to check my vacuum lines, disconnect one by one, clean the rubber conectors, and in the vacuum line that goes in the rear (next to the cabin) there is a plastic device that is rounded and allows air to go just on one side, but it was dirty, so it was letting the air pass on both sides. some carb cleaner and a Little shake were enough to make it work good. I connected again all the vacuum hoses, started the engine, and HALELUYAH!!!! the motor sounded very good. i went for a test drive and it feels very smooth.

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FINALY, AFTER ONE YEAR OF CHECKING EVERYTHING, THE PROBLEM WAS THIS TINY PLASTIC DEVICE (I DON´T KNOW ITS NAME). So, for all those who own a JEEP and are facing similar problems, PLESASE CHECK YOUR VACUUM LINES, SPECIALY THIS PLASTIC DEVICE, thank´s again Pat Yakis for your time and help.

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Hi Roland.

Where is this plastic device located

Please. Is it the same on the 2.7 diesel. I'm also having the problem with no acceleration.

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