View Full Version : Could someone check engine idle RPM...

04-29-2007, 10:01 PM
on a 5.7L 310? I'm just around the lower 600RPMs. I noticed today that I get a 'clunk' every so often while in gear with the thottle all the way back (any further and it goes to neutral). Best I could tell was that the noise went away when slightly advancing the RPM to around 700. No clunk, but a random stumble when not in gear. Makes me think my idle is too retarded.


04-29-2007, 10:43 PM
You can't lower the idle RPM easily (you can but the screw is painted). Make sure the idle stop hasn't moved or become loose. Make sure the flame arrestor is clean, the cap and rotor are in good shape, the plugs are newish and the wires or plug boots aren't cracked (just noticed one of mine is cracked on my truck). Raise the RPM in neutral to about 1200, remove the IAC plug (four wires, two green/one blk & one wht tracer and two blue/one blk & one white tracer), bring it back to idle and re-connect the IAC plug. You should hear it correct the idle speed. If it doesn't, it may need to be re-parked or the controller/IAC may need help.

The tach may not be totally accurate but the idle is supposed to be 650 RPM. Look for loose wires and grounds.

04-30-2007, 08:09 AM
One of the 1st few times out I had an engine idle issue where the idle would start to climb rapidly. I had found out that the issue was where the throttle cable attached to the arm that actuats the throttle/butterfly valve (sticking open). I corrected it that day after talking with my dealer, but since then the nuts had spun loose a time or two so I had to try to reposition them and put a little thread lock on them. Maybe I hit a point just a little too low?

I did not notice any paint markings. The dealer put PP on it, so I don't know if that would have affected having paint markings?

Thanks for the reply.

EDIT: Newer plugs about 25hrs ago. Cap and rotor good. Wires look good. Engine has less than 80hrs on it. :o

EDIT II: Does it make sense that if there is a slight engine miss at idle (while in gear) that it could be reflected by the noise the tranny seems to be making? Any other RPM it's gone and runs great...as well it doesn't do it while not in gear.

04-30-2007, 08:43 AM
When I said the screw is painted, I meant on the screw that actually stops the throttle plate from closing more. Look at the whole assembly there and see if anything is loose.

04-30-2007, 08:50 AM
Will do. I'll check that out.

My dealer said it should be closer to 700, so maybe it's set back too far. I'll do some digging tonight.

Thanks again for the help. I'll try it all!

04-30-2007, 10:38 AM
I found a picture that I had from a past (related?) issue. I have updated it to show what nuts had vibrated loose. Can their position affect idle?

04-30-2007, 04:55 PM
No. Remove the throttle cable from the throttle body and look at what keeps the throttle from going past the idle position. That screw and the IAC are the only things that would decrease the idle speed unless there was a fuel delivery issue. Run it and look at the shape of the fuel cone going into the throttle body. If it looks like part of it is missing, you have a clogged injector. Someone recommended dumping a can of Sea Foam into the tank and I agree- it won't hurt.