QuestionRoland,
We changed all the spark plugs and the problem got worse. It now feels as if it will die while driving down the road whereas before it only did this while stopped or on take off. As I mentioned before we had already taken the car for an $80 diagnostic, it showed nothing. Today my husband took the car to Autozone for their free "diagnostic" and it came back with codes for misfire on the 2nd and 3rd cylinder and throttle position sensor. We bought the sensor, only the manual states after installing we will have to take the car to the dealer for the TPS to be adjusted with some type of scan tool. What is that about? Also, will replacing the TPS clear the issues of misfire on the 2nd and 3rd cylinder? Thanks in advance.
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The text above is a follow-up to ...
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To make a long story short, our 99 Chrysler Sebring Convertible died last month. We replaced timing belt, distributor, distributor cap, 1 bad spark plug and new spark plug wires...finally the car is running! BUT, when car is stopped it seems to idle rough (as if it's going to die but it never does) and when we take off same thing. Once we get going down the road it's perfectly fine. We checked the EGR valve and it is not stuck (even sprayed WD40 as an extra precaution), we did replace the air filter and that seemed to help a tiny bit. We took the car in for an $80 diagnostic that showed NOTHING. Any suggestions, we are at a complete loss. Could it be something with the fuel system?
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Hi Karen,
'No code' engine problems are a challenge. On the ignition side of the equation I would want to verify that the rotor was replaced along with the distributor cap to which it mates. On the fuel system side, I would think about mixture rather than fuel supply itself which is usually not an issue at idle but rather at speed:
One maintenance item you might try is to clean is the throttle plate in the throat of the throttle body. If it get gummed up on the back side from the nearby exhaust gas input port it can cause poor idling. Remove the air intake hose and that should give you access to the plate which of course you open via the throttle lever arm (or have a helper step on the gas pedal). Use a solvent and cloth or q-tip to clean both sides of the plate thoroughly. Also clean the throat and the small passageway on the side of the throat which is how the idle air supply gets into the engine when the valve is closed. It is controlled as to its opening size by the tip of the automatic idle speed motor, which you can't see unless you remove the motor. The AIS has its own fault code 'set' so that doesn't seem to be the issue.
Because of the belt and spark plug changing, there could be a small leak in one of the seams of the intake manifold which will cause a leaning out of the mixture. If you idle the engine and then squirt very small bursts of carburetor cleaner or starting fluid from a pressurized spray can at closely spaced locations around the intake manifold plenum circumference, waiting after each squirt to listen for a speed up in the idle rpm, you might identify a point where there is a leak in the gasket that needs to be resealed. Spray very short bursts as you are dealing with a flammable liquid and if you can find such a product with a thin nozzle spray tip ("straw"-like) adapter that would help to focus the spray and eliminate flame risks.
Were all the plugs checked, and are they pushing 100,000 miles of service? That is the change frequency if the factory-recommended plugs are installed. Changing the rear plugs requires partial dismantling of the intake plenum so don't do that unnecessarily. Was the engine idling like this before any servicing, or did it start afterward, and if so what service was done?
Those are some of the simpler things to consider. Other than a more thorough test at a shop with an oscilloscope to observe the ignition pattern of each cylinder there is nothing else I can think of to try at home. You might try pull the spark plug caps, one at a time, while the engine is running to see if you can identify one that doesn't seem to impact the idle, which would be a sign that cylinder is not igniting well and needs to focussed upon for a cause. The rear plugs are unfortunately hard to reach.
Those are my ideas.
Roland
AnswerHi Karen,
I can't predict if the tps code 'clears' whether or not the misfire will clear, it would depend upon whether they were related to one another or not.
I believe the instruction about the tps being 'adjusted' is a misinterpretation of verifying that the "voltage readings when the throttle is open and the throttle is closed and that it varies smoothly in between" is in fact the case after the unit is installed by using a DRB to measure and observe that voltage. If you have digital voltmeter you cans do the "adjustment" yourself in a few minutes. I don't believe there is any way to "adjust" the TPS. It is either right or it is not, or there is a problem with the wiring which you will know by measuring its voltages as I will be glad to tell you how to do with a meter. Did they happen to give you the specific code for the TPS? There are two separate codes: either too high of too low.
On the misfire, all I can suggest is that you check the gap on those plugs or the torque of the plug is right. Unfortunately the #3 plug is on the back side of the engine. If you paid someone to replace the plugs then I would go back and ask them to check their work, particularly the identified mis-fire cylinders because the car runs worse after their work was done.
Did you check-clean the throttle plate/throttle throat/idle air by-pass passage?
As I review your initial question and my answer I see another suggestion (looking for an intake manifold leak) that may be even more relevant if in fact the manifold plenum was removed in order to replace the rear plugs and the engine ran worse afterwards.
The causes of misfire, as I said, are numerous enough to make me believe the best approach is to try and review everything that has happened in the course of the problem to try and focus in on those things that could have gone wrong in the repair process. Otherwise it means turning the engine over to a sharp tune up mechanic who knows the engine as that person has the highest likelihood of identifying the cause. If a Chrysler shop was involved, then I would be even more inclined to call their number on the work actually causing a deterioration and that they should make it right (or at least get it back to the status quo ante) at no additional cost.
So let me know if you have a digital voltmeter and I can describe the measurements to do after the TPS is installed.
I can give you the list of causes of misfire, but it will make your head swim or become discouraged. So try to take advantage of whatever leverage you might have with shops that you have paid labor cost to and try to pressure them to fix the situation at no/little additional cost. There is nothing specific about which cylinders are misfiring, the causes are the same, and it just says to look specifically at those two cylinders.
Roland
