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Hello,
I have a 2004 Jeep Liberty 3.7L, 110,300 miles with a rough idle mostly when cold when idle at higher RPM’s. I don’t notice any surging of fluctuation on the tachometer needle, just the engine feels shaky with a slight sputter. It is very noticeable when you put it in gear and you can feel the idle chugging. Once you accelerate it drives great and has plenty of power.
I don’t have any codes or any cylinder miss fires. I just installed new spark plugs yesterday, cleaned and inspected the coil boots, cleaned the throttle body, but no improvement. The plugs I removed actually still looked fine and they where clean. I just bought this vehicle used about a month ago so wasn’t sure how old the plugs where. I didn’t removed the IAC valve or the throttle body from the intake. Just opened the throttle plate and cleaned with tooth brush, throttle body cleaner and clean rag. I also cleaned the Mass air flow sensor with MAS cleaner.
A lot of research has told me this is normal for these engines due to a balance issue. I was just wondering if anyone out there had had similar issue and resolved it.
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Update! So I took off the entire throttle body and removed the IAC valve. It was all guncked with carbon inside the IAC housing and passage. I took and old tooth brush and cleaned with throttle cleaner the valve and housing along with the backside of the throttle body. Now at cold idle it runs like 80% better and not shaking nearly as much! I will keep you guys posted if I discover or do anything further!
Update 2. The rough idle when cold still exists. I checked the fuel pressure and it is about 55-58 PSI. With engine off and fuel system primed, the fuel rail looses about 4-5 PSI after about 5 minutes of sitting. I am not sure if this is normal or a sign of a leaking injector or bad check-valve in the fuel pump? I also did a injector balance test using my Autel scanner and disabled individually each injector at a time and the idle got more rough and you could feel it miss. So the injectors seem to be contributing properly. I still have no codes. If you actuate the IAC valve via my Autel Scanner to different RPM’s you can feel the engine shaking and struggling to hold the set idle by the scanner. Is it possible that maybe I just have a faulty IAC valve? thanks
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