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Matt
Matt, Engineer
Category: Jeep
Satisfied Customers: 21627
Experience:  Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
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2004 jeep grand cherokee limited. 4.7 liter v8. after i

Customer Question

2004 jeep grand cherokee limited. 4.7 liter v8. after i start it up. the rpms idle between 100 and 200. this is way too low. in park it never stalls out, but when i drive it any faster than 25 miles per hour when i come to a stop, if i do not stop hard the jeep with stall. if i stop slow the rpms will dip and i will stall. how do i get my idle higher. 550 i think is what its supposed to be at! i know 100 to*****too low. some times it will even drop to zero. i just bought the jeep 3 weeks ago
Submitted: 1 year ago.
Category: Jeep
Customer: replied 1 year ago.
i have cleaned the throttle body very good. replaced the gasket. replaced the tps and the iac from chrysler parts dept. ive looked for vacum leaks. i did a tune up. air cleaner is new. pcv is new. ive never seen a vehichle idle at 100 rpms. im stumped
Customer: replied 1 year ago.
btw it is not throwing any engine codes at all. i even clicked the ignition 3 times to see if it reads a code across the mileage but nothing. i have 3 scanners and nothing picks up. no codes on the dash at all.
Customer: replied 1 year ago.
but the check engine light does work becasue i unplugged an 02 sensor to see if it was working. and it is.
Customer: replied 1 year ago.
forgot to mention, it idles very very low but it idles smooth.
not looking for an answer of if it idles smooth then dont worry. no. pass my question up if you are that guy. thank you
Expert:  Matt replied 1 year ago.

Hello

I'd agree that this sounds like unusual problem

I'd say that there must be a vacuum leak ? I know you've tested for these already but the best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.

Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.

Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

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