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Please Help. Idle Problem

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Please Help. Idle Problem

Old 08-07-2006, 10:40 PM
91Stealth is offline
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Default Please Help. Idle Problem

I recently Bought a 91 dodge stealth R/T NA, The guy who sold it to me told me i needed a new idle air servo. I replaced it, but the parts were not exactly the same, old one was tan colored with the number E9T15271A and the new one was all black plastic with the number E9T15271C. It fits right on and seems to work, But my question is when the bad Servo was in it wouldn't idle and would die, when it was unplugged it would idle rough when cold then it was fine when it warmed up. since replacing the servo the car runs fine cold but dies when its warm. If i give it gas or am driving it will run fine untill i shift into neutral and coast (The car is a Manual) then it dies. I adjusted the speed adjusting screw on the front of the throttle body and it idles fine warm and 1000 but when its cold it idles at 2000 2500 untill warm, then goes down again. I am thinking i need to adjust the screw back to normal but what else could be wrong making it idle funny and what else can i adjust.
thanks for any help!
Old 08-09-2006, 12:20 PM
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Default RE: Please Help. Idle Problem

The throttle position sensor could be going bad. The idle screw you adjusted supposedly comes preset from the factory and does not need adjusted. Usually, when you have to start adjusting it, their is another underlying problem.
Old 08-11-2006, 02:22 PM
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Default RE: Please Help. Idle Problem

Thanks, Is there any way to tell for sure if that sensor is the problem, the car runs fine when there is any load in the engine just idles rough, since asking my question it started fluctuating, down to about 700 rpm up to 800 or 900 when at idle. It also lookes like the throttle position sensor can be adjusted by the screw holes? or am I looking at it wrong?
Old 04-09-2010, 03:36 PM
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Default Iac

Yes, you are looking at it wrong. The IAC is electronically adjusted. What you need to do is wait for the car to warm up then adjust (reset) the SAS (speed adjusting screw) until the idle speed sits around 400rpm.

In the 1991 and 1992 service manuals, the servo motor that is used to control the amount of air that by-passes the throttle plate is referred to as the idle speed control (ISC) servo (stepper motor). Later service manuals call it the idle air control (IAC) motor (servo type). Regardless of its name, this servo is used by the engine control unit (ECU) to control basic idle speed. The ECU also uses the ISC servo to adjust idle speed as engine load changes or increase airflow for the following reasons.
  • When the power steering oil switch is turned on
  • When the air conditioner is operating
  • To compensate for thinner air at higher altitudes
  • To provide assistance to the dashpot (turbo models) during cruising and deceleration
  • To assist in starting the engine
  • To provide idle stabilzation during hot starts (coolant temperature above 194F)
  • To provide additional air during cruising and acceleration

As shown in the configuration diagram to the right, the ISC servo is located on the throttle body assembly. It shares the by-pass air passages with the fast-idle air valve. Air is drawn through slots "before" the throttle plate, whether the plate is open or closed, and flows into the throttle body "after" the throttle plate. The ISC servo consists of a stepper-type motor and pintle. The motor has two stators, with two coils attached to each, and a cylindrical magnetic rotor, with alternating north and south magnetized strips along its length. Through the middle of the rotor is a lead screw that threads into the body of the ISC servo. The pintle is attached to the lead screw. When the four coils of the motor are energized in particular sequence, the rotor rotates 15 one way extending the pintle one step. When the coils are energized in the reverse sequence the rotor rotates in the oppposite direction 15 and retracts the pintle one step. Extending the pintle reduces the air flow going around the throttle plate, and retracting the pintle increases the air flow. Details concerning the design and operation of the ISC servo are in the 1990 Laser Technical Information Manual (Chrysler Motors publication 81-699-9002).

When the engine coolant is cold, the ISC step count is close to 100 (retracted). As the coolant warms, the ECU gradually reduces the step count to about 10 (extended). This can be observed using a MUT or datalogger. I rarely see the step count reach 0 on a datalog. The ECU will increase steps to adjust idle speed or to allow additional air through the throttle body for the reasons listed above. ISC step count often increases at higher cruise speeds and during WOT operation. When the ECU is placed in "basic idle speed adjustment mode", by grounding the ignition timing adjustment terminal and the selected terminal in the diagnostic connector, the ISC servo is adjusted to the preset warm-idle position (9 steps plus altitude compensation; at ~5600' ASL my ISC goes to 13 steps).

If the stepping motor in the ISC servo malfunctions, idle quality problems usually result. These problems can include unstable idle speed, high idle speed, and stalling. Stalling also may be experienced when shifting or when decelerating. This servo wears out over time (maybe between 50,000 and 100,00 miles?). If the internal coils are partially or completely shorted (that is, if low resistance is measured across the coils), it is possible that the ECU/ECM can be damaged. Current comes from the MFI relay (after a 20-A fuse) and grounds in the ECU; the ECU is not well protected from excess current in case of a short or partial short inside the servo.

If you suspect the ISC servo is bad, I suggest troubleshooting the device before replacing it. The service manual describes several tests. I describe one of these, testing the resistance of the four coils, in a section below. A thorough cleaning, also described below, may improve ISC servo functioning.

If you decide to replace it, Tallahassee Mitsubishi (FL, 1-888-825-5648) lists the ISC servo (part number MD628053) for $329.93 and sells it over the phone for a discount price of about $247 (July 2006). The same ISC servo (MD628053) is used on all Stealth and 3000GT models (SOHC, DOHC, DOHC turbo), as well as most DSM models and the Mitsubishi Galant (basically Mitsubishi/DSM cars that use the 4G63, 4G64, or 6G72 engines).

http://www.dsmisc.com/ recently opened (July 3, 2006) and sells brand new Mitsubishi (the Mitsubishi logo is molded into the housing along with part number E9T15292C) ISC/IAC servo motors for $129.75 (a price that can't be beat for a brand new part! In fact, I bought one.). Note that these newer servo motors are improved over the older models and the coils test at ~40 ohms rather than the 28-33 ohms of the original and older servo motors. The ISC/IAC servo I bought from DSMISC Auto had resistance values of 39.7 (1,2), 39.7 (2,3), 40.1 (4,5), and 39.7 (5,6) ohms. DSMISC Automotive also has a web page describing problems with the ISC and some testing tips (see their FAQ page). As the pictures below show, the design of this updated servo is slightly different than that of the original servo. I installed this ISC servo and it works perfectly, including some of my idle problems. 3000GT owners Patrick S. and John L. recently (2007) emailed me to let me know they installed one and it fixed their idle problems and has been working great. Both were impressed doing business with DSMISC Automotive.

Auto Computer Supply (ECM-ToGo) (888-326-8646, Houston, TX) sells Mitsubishi ISC servo motors for about $145 (July 2006). Give them a call for current pricing and availability. ECM-ToGO also has a web page for diagnosing ISC/IAC servo failure.

Foreign Auto Computer (800-241-6689, Tampa, FL) rebuilds and stocks Mitsubishi ISC motors for our engines. They offer an 18-month warranty. Give them a call for pricing and availability.

www.3si.org member SMTCapeCod provided the following tip. Our ISC servo is manufactured by Standard Motor Products, Inc. It is part #AC99. He paid $143 for a new one at Rock Auto. It has a black cover instead of a biege one. Go to http://www.rockauto.com/, select your year and model Mitsubishi car, and enter AC99 in their parts search text box near the upper right corner.

These instructions supplement the service manual's instructions for removing and installing the ISC servo. I provide some additional tips regarding cleaning. Please read all of these instructions before beginning this operation. The suggested tools include: a Phillips screwdriver, an 8-mm socket with 6" extension and wrench, tools required to remove the battery from its tray and the Y-pipe from the throttle body, a bench vice and a hand impact tool (eg. Craftsman part number 47634, 47763, or 47762, ~$20), a toothbrush (or similar tool), electrical parts cleaner (eg. CRC Lectra-Motive Electric Parts Cleaner part number 05018), safety glasses, and a spray lubricant (eg. Bel-Ray 6 in 1, or any thin-film silicon or "moly" lubricant that will not harm electrical contacts).

1. Battery and Y-pipe. With the ignition off, remove the negative battery cable from the battery. Be sure you have security codes for any devices that might need them before you do this. Remove the battery. If you cannot easily get access to the ISC servo with the just battery removed, disconnect the Y-pipe from the throttle body and move it out of the way or remove it altogether. I tied my aftermarket braid-protected fuel lines out of the way. I don't think the stock lines are in the way.

2. ISC servo. Press down on the release lever of the wiring harness connector and pull it off the ISC servo. You may have to wiggle it a little as you pull. Do not pull on the wires. At this point you can test the resistance of the four coils or wait until you have the ISC servo off the throttle body. To perform this test, measure the resistance between terminals 2 and 1, between 2 and 3, between 5 and 4, and between 5 and 6. The resistance should be in the range of 28 to 33 ohms for the original and older models, and ~40 ohms for the most recent model, which is after our 3S cars were manufactured (see http://www.dsmisc.com/). The results for me were 30.1, 30.1, 30.3, and 30.4 (same order as given above) with the ISC servo off the throttle body.

Using a socket and wrench, remove the two 8-mm screws, indicated by the shortest arrows in the picture below, which attach the ISC servo to the throttle body. A Phillips screwdriver can be used but is not recommended. Be careful to not drop the screws as you remove them. One of the screws (lower left) was missing on my ISC servo. The replacement is a M5x0.8 metric screw that is 15mm or 20 mm long. Pull the ISC servo out of the throttle body. Inspect the o-ring to be sure it is still in place and in good shape. As the picture below shows, the pintle had a bit of carbon deposited on it. I would guess this is from the exhaust gas recirculation (EGR) system. With the two pieces of the servo separated (see next section), the inside components looked clean and new.
Old 02-08-2012, 11:21 PM
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Default Same issue

I had this same problem with my 91 stealth and i adjusted the screw just as you did. It ran fine for about a month or two and just the other day my ecu burned out on me and it wont run at all. Idk if this is the same problem your having but i thought id throw that in there

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