91 Dakota 4x4 with the 318.
Seems to idle REALLY low.... almost dying.... tack kinda goes up and down between 400 and 600 RPM. However, SOMETIMES it idles smoothly at around 800 RPM and stays steady there.
This engine is throttle body.
Any Ideas on what I should do here? Just increase the idle a bit? There's not any hesitation when I get on the throttle, so I believe the timing is pretty good on it.

 

Probably IAC Idle Air Control valve. They tend to get stuck and seze up. Try to clean it and make sure it moves freely. You should have a screw you can adjust to move the rpms up if you need to on the throttle body if it is not the IAC.

 

What do I look for in searching for this IAC? I do have the Haynes manual for the truck... but wouldn't mind a head's up as to what I"m looking for.
Thanks.

 

The IAC valve (also refered to as the Idle Speed Control Actuator) is mounted on the rear of the throttle body.

The 1990 service manual gives the following steps on adjusting the ISC Actuator (please note: for whatever reason, all sources for the Magnum engines [1992+] say to not touch this adjustment screw; so, those with 1992+, do "at your own risk")
1) Start vehicle and allow to run for two minutes.
2) Shut off vehicle. Allow 60 seconds for the actuator shaft to fully extend.
3) Disconnect the wiring connector to the idle speed control actuator.
4) isconnect the wiring connector to the coolant temperature sensor.
5) Hook up a tachometer to the engine.
6) Start the vehicle.
7) Adjust the extension screw on the actuator shaft until the RPM is within the specifications shown:
- If vehicle mileage is less than 1000 miles, set to 2400-2500 RPM
- If vehicle mileage is greater than 1000 miles, set to 2500-2600 RPM
8) Shut off vehicle.
9) Reconnect the ISC actuator motor electrical connector.
10) Reconnect the Coolant Temerature Sensor.

Quick question: has this truck been sitting for a while (even if you told a friend to run it every so often). If so, and this is what mine did for a few days (I was gone for 4 months), just keep running it, and when I say run it, I don't mean like a grandma .

While your there, you might as well removed the ISCA and clean it and make sure its "home" is clean too.

 

Ok, looking through the Haynes manual. It sais that the IAC is used on the MPI system, which are on the 92's and later throttle body. My truck is a 91. I'm gonna taka a look see anyway, and see what I can find, but this stupid manual mentions NOTHING on idle adjustments or anything of the sort for the early throttle body used on the 91's. These books honesty burn by ***** sometimes. 15 pages on changing a tire.... but heaven forbid you have to adjust your Idle at all. I know 2 stroke engines quite well, and if my snowmobile was doing this, the air/fuel mixture would be my first point to troubleshoot.... so an IAC needing adjustment/replacement would make sense to me....
Oh well.... I'll hit the freaking thing with a hammer if all else fails.
Man... I had a 750 double pumper carb on my 350 4 bolt main.... that carb didn't even have a choke on it.... NEVER had a problem setting that up! What happened to the "good old days" of "Lots of fuel + good spark = HANG ON TIGHT!"?!

 

Ok. Went out and started the truck and watched the IAC. What's happening, is the arm is extending bringing truck up to proper idle, then "clickin" back in again dropping the idle down to about 400 rpm. Then extending and clicking back again right away. It's doing this repeatedly, thus causing the problem, and... if I don't give it some throttle it will stall when the arm retracts, and the rpms drop.
So... before trying to adjust anything, do you think this is being caused by a faulty IAC motor? Or Sensor? Or is there something I should be trying to clean before thinking about replacing parts? If it's a sensor, which sensor would cause this symptom?
The arm is literally comming out to where it should be... then instantly dropping back.... it's not retracting slowly.
Thanks.

 

Bump

 

I'm no dodge specialist, but know my way decently around most all cars. I pulled my buddies 88 into the shop tonight with the same problem everyone seems to be having. I dont know emissions like the back of my hand at all. But we are getting a hard bog, occasional backfire and intermittent highy idling I believe. The air pump on this particular truck is siezed, however, i dont think its a big deal. I haven't checked the cat, or thrown a meter on one sensor. But from looking at all the things you and others have tried, helping it bits at a time (just as any tune up would do). I'd say the little devil in our problem here is the EGR valve! If you understand how the emission and ignition systems work together it makes sense to me. The EGR being stuck open would toss the same amount of dead air into the intake at all rps, hence the bog on low end. The o2 sensor gets cold from being far too rich, signaling the pcm to crank up that timing up a pile of degrees. It does so, giving the intermittent high idle, and loss of torque. The loading up of the engine, and rich gasses in the exhaust cause the random backfires. Mine idles high for a while then then drops low (Often dying). This indicates what most, would think is a TPS, MAP, IAC, or vacuum leak.. But what I'm thinking is the PCM advances itself so much, while trying to counter with the IAC, that it maxes out on advanced and resets...? killing the engine from the sudden slap in the face retardation. I don't know about you gut but I'm cutting out a piece of tin, tossin down some black RTV and pluggin a couple vacuum lines after I get out of class tomorrow.... CSXfan a clogged Cat was a good try abd most likely the cause of your stuck EGR. I know on some vehicles there is a solenoid that controls it? Maybe one of the three on your pass valve cover? I haven't looked into what they control.... Anyways I'll let you guys know how it works out tomorrow! Oh and until the PCM gets out of closed loop it doesn't touch the timing I believe, giving you a false sense of hope everytime it runs decent for a little while cold.

 

So you're saying that you believe it could be the EGR valve causing my IAC arm to extend and retract repeatedly and intantaniously when the truck is cold? Truck idles up then I hear a "click" (the arm retracting), then the arm extends again and increases the rpm's.... then "click" again... and this happens repeatedly until the truck is good and warm. Also... if I give the gas pedal one good punch and let off right away... the truck stalls.

 

My 90 with the throttle body did the same thing. The IAC on port fi is a solinoid type deal that controls the amount of air the engin gets at idle through a port. On the throttle body you have a stepper motor, ICM, (idle control motor),that drives a worm gear that actually opens the butterfly to allow more air; like a carburator, and when the gears wear it will jump and lose idle and it takes time for the motor to try and catch up if it can at all, (it losestrack of where it is). It depends on where and how bad the gears are worn. Replace the motor/gear assy. it's mounted on the side of the throttle body and pusheson throttle plate lever where your accelerator cable hooks up.