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2003 Matrix wont idle down
February 4, 2011
Hi all! I'm trying to help out a friend of mine. She has a 2003 Matrix with the 2zz engine and it wont idle down, even after its warmed up. When you come to a stop and push in the clutch the engine races to 4000+ RPM (seems to be getting worse; it used to be around 3000). If you mash on the accelerator it will idle down to around 1000, which I assume is normal. I have it for the weekend and told her I'd take a look at it. Any thoughts as to what I should look for?


February 4, 2011#1
Sounds like there is some obstruction in the throttle body (carbon deposits or varnish that is gumming up the throttle plate) or the throttle cable is stuck or binding. Could at the accelerator pedal (linkage), the throttlebody side (cable end frayed and hung up on a bracket), or "stuck" inside the cable jacket due to corrosion or obvious side of cable damage (cable kinked or bent).

I'd start by inspecting the throttle body, give it a good cleaning cant hurt. Sometimes if it is really clogged up, the ICV valve (Idle-Control Valve) can get gummed up so badly, that it will act like the pedal is stuck. If it is related to the throttle cable, sometimes spraying a lubricant down the cable jacket (disconnect one end, spray in lubricant and let it wick all the way through) and see if it that helps.

February 5, 2011#2
Thanks for the suggestions. I had checked the cables for binding earlier and they look ok. I thought I found the problem when I took the hose off from the throttle body to the air cleaner box and saw that the vacuum hose to the air cleaner box was disconnected. It probably happened when she took the car to Walmart for an oil change and they changed her air filter. Reconnecting it didnt make a difference. I gave the throttle body and idle control a good cleaning, but it didnt make much of a difference. It looks like the throttle plate may not be closing the whole way, but its very close. It might stop about a millimeter or two before it hits the idle stop screw. Forcing it the rest of the way does get the idle to go down. The only way I could clean it any better is to take apart the throttle plate mechanism and I'm a little afraid that either the return spring will go flying or be impossible to get back on. Throttle bodies dont go bad, do they? I'll give taking the mechanism apart a try if you think its worthwhile.

I suppose the ISC valve could have a problem, but I'm not sure how I'd figure it out without trying a new one.

Thanks for your help,

February 8, 2011#3
Yeah, that throttle plate should be pretty much closed all the way. There is a bleed bypass hole that exits behind the throttle plate - that will allow enough air through to idle purposes. I agree, not worth taking the throttle body apart, unless you know that is the problem. The spring might not be the part to worry about, more likely I'd worry about damaging the sensitive TPS sensor.

Throttle bodies, in general, do not go bad. Mechanically, they are pretty simple. Usually it is the electronics, like the TPS sensor, that could be offset or reading incorrectly, causing the car to mis-read how far the plate is open. That would definitely cause idle issues as well as driveability issues. From your description, could be as simple as the idle stop screw was messed with by accident.

February 11, 2011#4
Thanks for all the help! At this point I'm tempted to say it is the throttle body. It appears that there is a worn spot that the throttle plate is getting hung up on that prevents it from closing the whole way. I'm thinking if the return spring was stronger it would force the throttle plate past that point, but I dont know if such a thing exists. Seems a shame to replace the whole throttle body for something so simple.


February 15, 2011#5
Just for closure, it was the throttle body. While I doubt many, if any, others will have the same problem, the problem was the throttle plate getting stuck on the throttle body. As it opened it moved slightly off center, then when it closed it rubbed against the throttle body, wearing a small indentation into the throttle body, and got stuck. For some reason, it only happened while driving. I could move it back and forth by hand and it would never happen. I fixed it by adding a spacer (a thin washer I pounded out of a loop of wire) around one end of the throttle plate shaft. It keeps the throttle plate from moving off center. Hopefully it wont fall off.

fishexpo101, thanks for all the help!


February 18, 2011#6
Thanks for posting your resolution to your topic. Pretty bizarre way to get stuck, but anything is possible with clearances the way they are. Nice "MacGyver" fix on the throttle shaft to take up the slop - quite ingenious!

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