What causes an M42 to idle nicely at 2k?

[adam12hicks]

I don't WANT it to idle at 2k  I want it to idle around 1k assuming that's where it should be.  I have removed the ICV, cleaned it and lubed it, and tested it for resistance and put 12v on it and it clicked and went nuts, so I assume it's good.  What else should I check?  The rest of the vacuum looks solid on the nasty vacuum mess.  The o2 sensor doesn't have anything to do with idle does it?  I'm thinking not?

Thanks for any tips!

[tjts1]

Check that your the throttle linkage and throttle body. The upper throttle plate might be stuck part way open.

[adam12hicks]

Will do.  I just had the throttle body out and cleaned up, but I didn't notice if the plate was sticking.  What would cause it to stick?  The spring or just gunk in the pivot shaft (for lack of a better term!)

Thanks!

[tjts1]

Easiest thing to check is the if the cable itself is properly seated at the TB end. It might just be caught on the linkage. hard to describe. Pull on the cable or rotate the throttle by hand. See if it travels all the way to its stop when you let go with an audible click.

[adam12hicks]

Yeah it's seated properly.  The cable itself is broken on the plastic piece that connects to the throttle body, so I had to epoxy it together.  The cable actually has about 1/8-1/4" slack let-up before grabbing the throttle body lever, so I don't think the cable is causing any type of sticking.

The other odd thing (which I should have mentioned!) is that when I first start the car it idles nicely around 1k or so, but after I drive it for a few minutes it stays back around 2k from then on.  So it's not acting like a cable or mechanical issue in that respect.

Thanks tjts1 for the assist!

[adam12hicks]

BTW  I just did a stomp test (never have before) and got a 1271, which looks like Ignition Coil 1.  I haven't noticed any coil problems, and I don't expect this to have anything to do with the idle but I thought I'd mention it.  I am going to track down another coil anyways just to swap it out.  Not sure if the code will go away on its own or if it needs some sort of clearing proc.

[Matt-B]

check throttle position sensor??

GL

[colin86325]

Check that your throttle plate is set back to stock clearance when closed.  Sometimes the stop screw is adjusted to make the idle higher to avoid a lumpy idle.  You need this baseline check to perform any further tests accurately.

Also, since it's broken, replace your plastic cable clip that snaps into the arm of your throttle body. Should be less than a dollar. A new throttle cable will set you back about $20, and is recommended.

[adam12hicks]

Cool thanks Colin... any thoughts on how difficult it is to replace the throttle cable?  Is it one cable from the accelerator pedal to the throttle body?

[colin86325]

The prices might be slightly off but not by too much.
Not a difficult job. Note which position the cable mounts to in the throttle body arm (there are 2 possible locations)
Remove the knee bolster and panel under the steering wheel.  Pop the cable hook out of the mounting point on the arm of the accelerator pedal.  Make sure to retain the small rubber grommet on the cable hook if it comes out with the cable.

It might be easier/quicker if you intentionally destroy the plastic pinch-clip that holds the cable to the firewall (by the brake booster), than to try to gingerly remove it by compressing the tab. Just don't go Captain Cro-mag on it and bash the firewall in.

Install the new cable in the pedal arm, making sure the grommet is in the pedal arm, then connect the throttle end.  Adjust the cable as necessary by turning the nut on the end of the cable.