Idle "sticking" at it's last point. Suggestions?

[rjd2]

Hi all-I am in a "shakedown" period on some idle issues I have been chasing. I've made some progress, but am having a strange behavior at my current stage: the idle will have a habit of sticking or pegging at a particular RPM. So, for example, If I start the car, and it sits at around 900RPM(or 1100, or 1300RPM), and I dont touch the throttle, it will often just hover at that RPM. If I goose the throttle, it will often peg at a new position, often in the 1100-1400 range, but sometimes below 1000. Here's where it gets strange: If I am stopped at a light, in neutral, and the idle is pegged at (for example) 1300RPM, if I put the car in gear, and ease out the clutch to drop the idle to maybe 800, and then depress the clutch again WITHOUT touching the throttle at all, the idle will peg at 800. I've verified the idle switch is working, the idle ECU has power, the idle speed motor has been verified to be working properly, and I have a new thermister/O2 sensor/WUR unit/distributor in the car.

Any suggestions? Thanks for your thoughts.

[eight8toy]

Mine did this a bit awhile ago so I lubed up the throttle cable with some grease and that seemed to fix my issue.

Actually just where the cable exits the sheath in the rear so it didn't take but 20 seconds to apply. Then manipulated the linkage a bit while the car was off to get it spread out some.

[rjd2]

Mine did this a bit awhile ago so I lubed up the throttle cable with some grease and that seemed to fix my issue.

Actually just where the cable exits the sheath in the rear so it didn't take but 20 seconds to apply. Then manipulated the linkage a bit while the car was off to get it spread out some.

Thanks. I actually had the throttle cable lubricated already, and I had visually verified that it wasn't catching, with someone else in the car working the pedal. Since it will "hang" at points from just the downshifting pressure of letting out the clutch, with no action at the throttle, could it still theoretically be the throttle cable?

[Jonathan]

It also sounds to me like it is the throttle cable or spool sticking. Mechanically sticking that is.

I have more experience troubleshooting automatics than I do manual transmission cars, but perhaps there is a connection between you putting the car in gear and the vacuum developed by the engine pulling differently on the butterfly valves in the intake. Those valves pivot on the inside of the intake and at that same pivot point on the outside is the bracket and arm that move and push in the idle microswitch. If your system is already not moving freely or easily, that extra change in resistance could be the difference in idle RPM.

If you have your helper again, you can confirm that when the engine is idling high, you can't physically push (with your finger) on the end of that lever arm and force the peg in to engage the idle microswitch. If you can get the idle to come down by pushing on it with your finger, it means it isn't going back to its rest position completely on its own. You may just need to lubricate more than the cable alone and also do the spring that is wrapped around horizontally on the throttle spool assembly and also the spring that is wrapped vertically around that pivot point where the butterfly valves and idle microswitch lever arm meet.

Part of the throttle spool recall, in addition to the part about the deice shield, is to prevent the far end of that throttle cable from hanging up on the edges of the throttle spool as it rotates. This was done by pushing on four separate circular clips over the stud on the spool bracket and what it was meant to do was keep the open end of that cable in its little groove and not catching on the edge of the metal.

You could take some pics of your throttle spool, cable and lever arm and post here and someone could probably confirm whether there's something amiss with all of that.

[Rich]

Have you verified the the throttle is fully closed when the engine idle is high? A visual check of throttle position like you mention isn’t always accurate. Next time the idle hangs pull over and, while it’s stlll high, try pushing the throttle lever closed by hand or with a screwdriver - see if that lowers the idle or not.

The result will point you in the right direction - mechanical or electrical.

Am now seeing this was written during Jonathan’s reply. My reply here is in line woth his 3rd para.

[David T]

Check for play on the ends of the quadrant link, the piece of linkage between the throttle spool and the throttle arm. Make sure it is being pushed all the way to idle, closing the butterlfys.

[rjd2]

Thanks guys! I'm going to focus my energy on verifying whether the throttle fully closes. All I have technically done is verify that the idle switch engages consistently "at rest"(it does).

Rich, thanks for that. Is the throttle lever the linkage bar that connects the spool to the idle switch?

[Jonathan]

Thanks guys! I'm going to focus my energy on verifying whether the throttle fully closes. All I have technically done is verify that the idle switch engages consistently "at rest"(it does).

Rich, thanks for that. Is the throttle lever the linkage bar that connects the spool to the idle switch?

There are some pictures in this post (http://dmctalk.org/showthread.php?10...l=1#post152181) of that lever arm as well as a portion of the linkage bar that David mentioned.

The lever arm itself is this part: http://store.delorean.com/p-6407-lever.aspx

And the linkage bar, called the "rod, assembly throttle" is here: http://store.delorean.com/p-6409-rod-assy-throttle.aspx

Basically, as you press on the gas, you are pulling the cable towards the front of the car. At the other end of the cable, in the engine bay, it connects to the throttle spool and as it pulls, it rotates the throttle spool. The linkage bar connects to the bottom side of the throttle spool on one end and the lever arm with the other. Both connections are "ball and socket" type much like the way your door struts are, only smaller. There are also tiny pins that slip in to keep the socket from falling off the ball. Both ends have adjustments for length. This is what David mentioned and it can correct some slack or slop in the response time to pressing the gas. I don't think this is where your trouble is though.

When the spool rotates from pulling on the throttle cable, it pushes the linkage bar towards the lever arm. That push goes to the bottom portion of the lever arm, where the pivot point is in the middle (across from the butterfly valves located inside the intake), and so the top portion of the lever arm goes the opposite direction from the push at the bottom, which means out and away from the little pegs that touch the idle microswitch. If you give the car some gas, you pull on the cable, which pushes on the linkage rod, which then pivots the lever arm (and butterfly valves) and deactivates the idle speed motor by releasing from the idle microswitch.

Notice how we are talking all air here and not actually gas? When those butterfly valves move (or pivot), they are opening and this lets in more air to the engine. When that air is allowed to come in, it then pulls down further the air pressure plate (the round one) that is located under the plastic air housing where the air filter is. This is the one we hear mentioned about pushing down on after you shut the car off to see if you still have rest pressure if you're trying to troubleshoot a hot start problem. The first actual connection to the fuel system is on this plate and it comes with a physical lever arm (a separate one to the one we were discussing) that changes the fuel pressure within the fuel distributor when it moves. It is a direct connection or correlation so more air pressure plate moving means more fuel pressure. It is this balance on the pressure plate and lever that is adjusted when you make a fuel mixture or CO adjustment. Meaning, how much air goes with how much fuel.

But anywho, that's more background info then you really need. I think if you spray some lube on those two springs we mentioned, your problem goes away.

[rjd2]

brilliant explanation, Johnathan. Thanks much! Will dig in to some testing today, much obliged!

[rjd2]

ok, so i went through, and lubricated all points at the throttle spool, butterfly "flaps", and the spring at the intake. i tested it manually at the throttle spool, and at least visually all looks rights. here's what i'm experiencing:

1-the "upswing" of acceleration, i.e. the throttle response, seems normal. the "return" to idle still seems abnormally slow. the engine decreases its RPM's slower than the increase.

2-once the engine warms up, if it stalls out, it will not start until i let the engine cool down slightly(this, i now remember, was one of the initial symptoms that caused me to do the thermister). i have to walk away for 2-5 minutes for it to start.

3-if i do my testing outside of the car, at the throttle spool manually, i notice a random knock or tap, as though one of the cylinders is having an issue. this is not regular, but comes and goes.

in general, the idle will hold at either 850-ish, or 1100-ish, so not terrible, but not perfect. any thoughts/suggestions welcome, thanks folks!