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First some info about the car. 2000 Chevy Cavalier Z24 2.4L with 4T40E transmission. 155,000 miles on the car. There are no problems with acceleration or maintaining speed. Engine idle does stay high if you are driving and put it in neutral. RPM’s are higher the faster you are going. A week after I got the car it gave a code for a bad knock sensor. I don’t remember what the code was. Knock sensor was replaced and code never came back. The only code I get now is P0300. I replaced the spark plugs with NGK Laser Iridium plugs. The idle was still bad and still getting P0300. I was going to clean the EGR valve today. The car doesn’t have one. I found what looked like a mounting location for a part that is no longer installed. It is on the front of the block on the drivers side. there are 3 holes for bolts to go in and one hole that is about 10mm wide that goes into the block. I have found and fixed several vacuum leaks already and used brake cleaner to find any that are left with no luck. The car looks like it had been sitting for a few years so I planned on replacing parts to avoid any future problems. I started with the IAC and TPS. It looks like the camshaft housings were both removed at one time due the all of the blue “gasket” oozing out where a real gasket should be. Recently changed the headlights and found out they were not even the correct bulbs. On top of that they were being held in with zip ties. I am not looking forward to finding the next “repair” the previous owner made. Any help I can get would be greatly appreciated.
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check your spark plug wires might help. I would just pull them one at a time and hold them close to the spark plug and see if you get spark.
also I would look for more vacuum leaks around the car for the higher RPM. you can you some break cleaner and spray it around the upper and lower intake near the gaskets and also on the tubes and hoses your are suspicious. if there is a leak where you spray your rpm will rise. BE CAREFUL WITH WHERE YOU SPRAY. IT CATCHES ON FIRE PRETTY EASY. NO WHERE HOT.just my 2 cents
Thanks for the reply. Unfortunately there are no plug wires. It has an ignition control module that mounts right above the spark plugs. It connects with plug boots. I have also sprayed around the intake manifold and the rest of the vacuum system with brake clean and found no vacuum leaks.
The 2.4 was bad about cracks in the housing where the coils mounted. I’ve ran into this several times and as bad as it pains me to say dealership parts have given me the best luck when replacing them. Stay away from bargain basement part store stuff with these. I really think you may
have more issues than that though. Any more info you can share?Unfortunately that is all the info I can think of. I didn’t look at the coil housing too much when I changed the plugs. I will have to do that in the near future and see if I can find anything. I have found that people on other forums who have changed them didn’t fix the problem they had. I have been putting it off thinking it was a dead end repair, but I will look into it. Thanks.
I don’t think the coil packs would cause a high idle. That sounds more like a vacuum leak, but you’ve said you’ve already checked for those. Given the condition of the rest of the vehicle, you may have some other issues going on like a wiring issue or something like that. The check engine light code you have is for a misfire. Perhaps check the compression to see if all the cylinders are putting out. If not, this can cause a rough idle. You might also want to check fuel delivery. A power balance test can also help you nail down a problem cylinder. I have some more detailed information on diagnosing idle problems and performance problems, as well as how to perform a power balance test in these articles.
http://www.ericthecarguy.com/faq/solving-automotive-idle-problems
http://www.ericthecarguy.com/faq/solving-automotive-performance-issues
Hopefully that info is helpful. Keep us posted.
Ok, just got done with a power balance test. I unplugged each fuel injector one at a time and they all caused the idle to drop. I have gone over the vacuum system but today I did find another vacuum line that I can’t account for. It goes from the accessory vacuum connector on the throttle body into the cabin somewhere. I lose it after the firewall in the engine compartment. It is wrapped up with a bunch of wires on the driver side and secured in a wire sleeve and that’s where I lose it. After some digging through a repair manual I found there is a heater and A/C vacuum harness in the dash. What does vacuum do in an HVAC system and are they prone to leaking? Thanks Eric for this forum and all of the vids. Just found out about them last week and I am already a fan. Keep up the good work.
The vacuum in the HVAC system is what makes your doors move to select between heat AC and position. You know that little whoosh noise when you move the HVAC controls? That’s the vacuum moving the doors. They do leak sometimes but usually you’ll notice the lack of control of the doors. (you lose heat/AC/position control)
I just thought about it when I got done posting. I was just looking at it when I was doing the power balance. I will get a pic and post it sometime tomorrow.
Awesome I believe you may have found the lack of your erg valve if I’m thinking right. Jared my memory when I reread your first post. Don’t hold me to it but I’d recognize it if I see a pic. The egr was in that general vicinity I believe. This could be source of a rough idle too if removed and not properly sealed off.
[quote=”Twilightsteel” post=85226]Well that’s not a problem then. That’s something on the car that works just fine lol.[/quote]
LOL
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