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roybelding, ASE Certified Technician
Category: Jeep
Satisfied Customers: 6176
Experience:  My knowledge of Jeeps from the early 60's till present. Love to help people with there issues.
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Liberty: Mark,I have a 2002 jeep liberty, at low RPM the

Customer Question

Hi Mark,
I have a 2002 jeep liberty, at low RPM the engine shaking alot. OBDII codes 152 and 306 appeared. the following troubleshooting was performed:
- coils checked found ok
- IAC sensor cleaned
- TPS checked
- PCV valve checked
the mechanic said that the PCM is defective.
i am not convinced, is it possible that the intake valve is stuck?
Please advise
Submitted: 2 years ago.
Category: Jeep
Expert:  roybelding replied 2 years ago.
good morning my name is ***** ***** I will assist
the 306 is a miss fire code. you need to check compression, check spark plug, which is the first thing I would replace, check coil and the boot, look for a leak of vacuum at the intake, check injector and wiring and lastly the valve train.
the IAC itself cannot be cleaned as it is a sealed unit. the issues when they fail are internal. you just cleaned it externally. the passage must also be clear of any carbon to work correctly.
as far as a pcm failure??? not at this point. it is the very last thing I would consider and that is after all other possibilities are exhausted.
Customer: replied 2 years ago.
thank you Roy,The coils were swapped the error didn't change
Spark plugs were replaced.
Injectors were removed and cleaned, their seals were replaced by new ones.
No air leak was detected.whenever the RPM is higher than 2000, the vehicle runs smoothly. whenever i turn it off and on again it works fine for few minutes than it start shaking and does not get a response from the throttle pedal unless you push it down to the there a way to check the train valve without having a compression tool?
can a defective IAC generate this failure?Please advise,
Expert:  roybelding replied 2 years ago.
ok. thanks for the update
1. I see you had the injectors cleaned but did you check the resistance across each one?? you can have a bad injector from an electrical point.
2. there were issues with exhaust valves sticking and not closing all the time. compression test would be good but using a vacuum gauge at idle would be able to tell this by watching the vacuum and see if it fluctuates instead of being steady.
3. I doubt a bad IAC would give this condition.