I asked a similar question last week but I didn't get very many answers...

When I let off the gas or push in the clutch in my 02 Z28, the rpms sometime hang for REALLY long time at around 2000 rpm and sometimes it wont even come back down until I'm at a complete stop. What's going on folks?!

FYI I just changed plugs and oil and it was doing it before that too.

 

have you had it scanned for codes? sounds like the maf may have issues. could also be the temp sensor or 02s giving bad numbers.

 

Oh yeah thats right! You did say that on the last thread haha and no I still have not had a chance to scan it yet. Perhaps tomorrow I can... Annnddd... I keep getting different answers from everyone when I ask if you can have a code without a check engine light. So can you? Because the light is not on so... I dunno. Some say the light only comes on if there are ANY codes at all and some say that there can be codes but the light will stay off.

 

unless its an ongoing problem it will not stay on. alot of times a sensor is failing only when cold or at a certain temp or condition, like the throttle at a certain place. the light might come on for a few minutes or seconds and go off. the computer needs to see a failure three times before it will store a code. on the newer ones like you have it should also have a list of failures that did not come up three times and with the right scanner they should show.

 

Coolio I'll try to go and get it checked tomorrow

 

Fixed it! Well at least it seems like I did. I did a lot more research and I kept on seeing people talk about their IAC. So I took it out and sure enough it was SUPER CAKED on with black nastiness! I cleaned it off with throttle body cleaner and I also sprayed inside of the IAC hole. Each time I sprayed I would take a paper towel and wipe down in there with my finger and I kept finding all kinds of gunk

When I first bought it... I looked inside of the silicon elbow (I think it's the SLP smooth flowing one) and there was a lot of dust in there. That worried me... so I took it off and looked in the throttle body and found a good (or bad I guess haha) amount of grime in there. I sprayed that off with throttle body cleaner as best as I could. My point is... I think that the previous owner had some kind of filter problem and that's why all of the parts are nasty.

But anyways... After I cleaned it and left the battery unplugged for like 20 min. I fired it up and let it idle for a while. Right away I noticed that it idled lower than it used to. And after I drove it around my neighborhood I noticed that the RPMs fell MUCH faster than they used to. I know the computer still has some learning to do, but I think that this problem is solved

So now that I know that there was alotta dirt in just those two places... is there probably alotta dirt in my intake manifold? Anywhere else? Should I worry about it? If so how should I clean it?

 

Considering all the dust and dirt you found ,sounds like the car was run minus air filter or there is a leak in the intake plumbing. Make suer the air filter is there and all clamps tight, and no leaks.

 

There was a new paper filter in there from the dealership... but I had a KandN left over from my V6 so I threw that one in after I cleaned and oiled it. And the intake is leak free. I'm about to go seafoam the thing so hopefully that will help any damage the last guy did!

 

So I'm going to awake this old thread because I made a new discovery. I was a little mistaken about when the rpms hang. If I shift out of gear without pushing in the clutch... (I don't know if anybody else does it... but if you put a little bit of pressure on the shifter and tap on the gas it will easily shift into neutral. I used to do it all the time in my Jeep and V6 Camaro.) THATS when the rpms will hang! It's almost like the car thinks that I'm still in gear and that I'm just decelerating. BUT if I shift into neutral by pushing in the clutch... the rpms will drop quickly.

Why does it do that? Now that I know when it happens... I know that it's not a problem. But I still wanna know why the car does that.

 

happens in my v6 maro to, idk why it does it but i dont think its a big deal