1997 Plymouth Voyager UNUSUAL IDLE

SHORTY1960

MEMBER
1997 PLYMOUTH VOYAGER
6 CYL
2WD
AUTOMATIC
157,000 MILES

Even though my mini van has high mileage, It still has about 98% of engine compression still left. It still runs great, but my question is that why does my engine idle smothly during the summer months, but somewhat erratically during the winter months? In the drive position, while stopped, after engine has reached normal operating temperature, the R.P.M's sometimes dips to about 490 to 510 rpm, then it goes back to it's normal 670 rpm to 725 rpm if accessory is turned on, but during the summer months, it stays on 670 rpm in drive, and 725 rpm with A/C on, and running smoothly. I always check for vacuum leaks, and also frequently manualy clean the intake plenum, and intake system. I frequently change the oil, tune-up the minivan, change the fuel filter, change the trans fluid and filter, you know the works, but what happens puzzles me, so if anyone know the answer to this question, please let me know.

1 Reply

CH112063

MECHANIC
1,320 POSTS

You have explained your problem well. And your maintenance.
Your van(3.0L or 3.3L or 3.8L)) is a well built and fine vehicle for safe and comfortable driving. Its vision while driving is second to none. No surprise it has lasted this long, or that you are probably correct in your engine compression readings. Two valves, closed tightly, are the best way for combustion(expsnsion) to occur. As long as the spark, fuel mixture, and power is brought to the crankshaft in an efficient manner, without any pre-ignition.
Working for Chrysler since 81 in a dealership, on flat rate has brought my appreciation of both engines and their methods of control to bear on my life and experience to a very high level of appreciation, as my two cars are older smaller and also a pleasure to drive.
Your intake maintenance has shown you the throttle blade with two of its main idle controls attached. One judges the position of your decision of throttle opening. The other changes the air allowed to enter at the correct position in the throttle body and at the correct time. Your computer senses the angle of blade, and control its air intake, in addition to your selections(for many demands). Take them off, all the assembly with the sensor and motor(idle) are somewhat serviceable. Clean the idle motor plunger and its bore with a nylon brush and carb. Cleaner. Wear gloves for skin protection. Protect your eyes and breathing if you can. Take a good look at both connections(male, female). Squeeze em to tighten them. Be gentle, use electronic tools. The intake coolant sensor, and the engine vacuum sensor all work together with these two to give you all types of engine speeds and timing. After your done, re-connect the battery(remember to always disable the 400 amps and 12 volts waiting to get to ground at all times) then let it run. After hot, you'll know if any are still bad and need replacement. This is what I have always referred to as the gang of 4. TPS, IAC, CTS, and MAP. There are many more possibilities for problems that affect idle speeds, but I feel, the way you take care of the engines air and fuel filters, we should start with a little TLC. Any info on this is available at this powerful information site, and from its many certified experts, and me too. OK All these(except coolant) use three wires for the whole process. The coolant sensor(in 97) had only two, I believe, and you can just do the wiring on the MAP and coolant sensors. MAP needs intake manifold vacuum, so make sure it has it. Good evening