Questioni have a 99' 300m that has 130k on it. the problem is on startup it idles very rough and then smoothes out after driving a bit. it sets a code #2 cyl. misfire, cleared the code and about a week later reset #6 cyl. misfire. now every time i start the car cold it idles rough, the light blinks then stays on. my question is where do i start. the engine is a 3.5.
AnswerHi Michael,
Let me suggest you start with the egr valve. I would take a look at the exhaust gas recirculation valve which is located behind the engine near the air intake throttle valve. It is mounted in a pipe that runs between passenger side exhaust manifold and the air intake manifold. The valve is mounted horizontally and has a valve stem between its round vacuum actuator top and the body of the valve attached to the pipe, inside the flange that connects the two parts. The stem has a slot into which you can insert the tip of a flat-bladed screwdriver so as to lever the stem back and forth against spring action which should move freely and close tightly. If the stem seems to be sticky so that stem doesn't close all the way by spring action, then you can try spraying some penetrating solvent like WD-40 on the valve stem to freeup its motion.
If the valve is sticking slightly ajar it will make for a rough idle and poor acceleration such as you describe because the mixture is too dilute. It is one of the most common causes of this symptom. So see if you can find the valve and check/lubricate the stem. To check it in motion you can rev the engine from idle to 2500 rpm and back to idle and watch to see if the valve stem moves freely in both directions to the extreme open and closed positions. It may be that the interior of the valve is cruddy so that might require that it be unbolted from the pipe where it it attached and cleaned. But chances are good it will only be a sticky stem.
As to the misfire codes, if the egr turns out to not be the cause, here is how I responded recently to another 3.5 owner who had similar codes:
"The codes are based upon the detection of minor missing which causes subtle differences in the rpm as each cylinder fires to produce its rotational input (crankshaft speed sensor is the detector involved). The Chrysler troubleshooting manual lists the possible causes as:
secondary ignition wires, puel pump or fuel filter, injector harness connectors, ignition coil circuit, spark plugs, mechanical engine problem, contaminated fuel, water in fuel, PCM grounds, Injectors, Restricted exhaust, intake restriction, PCM, evap system, EGR system, Air gap at high rpm's, damaged sensor trigger wheel, and intake manifold gasket leak. That is quite a list!
The approach suggested is to check all electrical connectors and wiring, then do the tests in the following order:
secondary ignition
fuel delivery
engine vacuum
PCM power and ground connections
engine mechanical
The first one uses an engine analyzer scope to look at the high voltage pattern, then spray water on the cables to see if it changes. The possible repairs: individual spark plugs, coil or cable replacement
The second one involves pressure measurement and from there a variety of possible solutions
The third involves reading the intake manifold vacuum to see if it is steady at between 13 and 22 inches of HG. and if not the suspects depend upon the pattern shown by the gauge.
The PCM involves checking various wires at the PCM plugs
The last involves engine compression testing and a variety of other mechanical checks.
So I guess that beginning with the ignition wires makes sense unless you have a scope and the experience/knowledge at interpreting the patterns. You might try looking at the wires in the dark with the engine idling, then also spray some water mist on them to see in either case if you see arcing which would be a sign that the wires' insulation is breaking down. Then measure the coil resistances. (Between pin 6 of the 6-pin connector and pin 1 of the 2-pin connector at the distributor/coil it should measure 0.6 to 0.8 ohms; between the coil tower and the pin 1 of the 2-pin connector it should read 12,000 to 18,000 ohms, this measurement requires removing the distributor cap to measure at the internal coil output tower). If it passes that, then focus on the fuel filter and pump.
The codes pointing to cyls 1,4,6 mean the general problem is affecting those cylinders more than the others, but the approach to it is identical to that for the general misfiring problem, perhaps with a focus. But the 0300 code is probably the controlling factor (involving multiple cylinder misfires rather than just one).
An intake manifold gasket leak can be detected by applying very brief squirts of starter fluid around the gasket while listening for any change in the idle speed immediately after each squirt.
I can't give you any personal experience with this situation, unfortunately.
I'd be interested in learning what you find to have been the solution."
Roland
