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Discussion Starter · #1 ·
Hi there,
I'm a french owner of a 2004 WJ 4.7 HO (sorry for my english) and I am facing a problem I cannot solve.
Each morning, on cold start, I got a low/rough idle at 550/600 rpm 10 seconds after starting the engine (car shaking a little bit) but NEVER STALLS. Outside air temperature doesn't seems to have any effect, it occurs every time on cold or warm conditions with the same rpm.
More, sometimes during these cold starts when idling, I got MIL on with codes P0300, P0304, P0306 (random misfires)
If ONLY occurs on cold starts, never when the engine is at normal temperature. I can remove the codes by disconnecting the battery but they are back 2 or 3 days later.
Except that, the car is running perfectly, no other problem at all.

So this is the list of things I've done or checked...
-New plugs
-New set of injectors (upgrade)
-Checked for compressions (everything is ok)
-Checked for vacuum leaks (didn't find any)
-Swapped plugs and coils (same cylinders on misfire error)
-New IAC valve, new PCV valve, new air temperature sensor
-New set of intake manifold gaskets

What should I look at next ? LTFT and STFT ? EGR ?
Any idea will be highly welcome !!!

Thank you Guys

The beast from Brazil
8,310 Posts
If you have a scanner, for sure i would check the STFT and LTFT figures. They should be +- 10 %, if a lot over or under the +- 10%, there must be something wrong. (you must count the STFT and LTFT together to get the value, so if STFT = +3 and LTFT = +7, the value will be 10%)
The problem can be sticking valves. Run some seafoam or a product alike through the brake booster line and let the engine soak for an hour, to let the product do its job. When you run it again, a lot of white smoke will come from the exhaust, so probably not a good idea to do this in a busy place or with difficult nabours.
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