Hi all,(2000 V6 3.8 5 speed 93 Octane tune - 98 block with my original split port heads intakes yada yada) have a few quick questions, my stang will not go through the warm up cycle, it's as if it just starts up and sometimes struggles to maintain idle, and will dip down to about 400 rpm occasionally, sometimes stall, but when it does maintain some sort of idle, it will not idle above 900 rpm. It will even idle at about 6-700 for about 7mins surging up to 900rpm occasionally, and right back down to 700. I can not drive it, because I feel like it'll eventually stall. I am positive my maf is good, checked the voltage and tested it. I had a spare IAC laying around so I put that one on just to check, and it seems to be working, by maintaining some sort of idle. I also checked the dtc's with my tuner, I have the codes written down somewhere, but I started to get a lot of weird codes at once, like the fan relay, and ac clutch relay to start with, although BOTH of them are working normal.... my question is, as far as the idle issue, is there anything else that I could check? Also as a side note, I have a few coolant temp sensors laying around, I know one of them is good, I've swapped multiple and still my temp gauge will not read even though I can feel the motor is warm. I do show the P0511 - Idle air control circuit - code, not sure if it's just lingering or what.

 

Normal idle should be between 500 & 700 RPM’s. My wife’s ride jumps to around 900rpms for about 20 seconds after startup and then drops down to normal.

If you have an IAC code then that may be your problem. IAC (Idle Air Control) valve is what lets enough air into the motor at idle. If it is bad or the circuitry has a problem then the computer can’t maintain the idle properly. I would start by tracking down that code (and the others). Most likely they are causing the problems your seeing. Good luck...

 

Thanks bud, I'm thinking it's the circuitry, because initially, it will hold idle at 400 rpm or so, then jump up to about 700 and idle there for about 7 mins (all the while trying to surge to 900 rpm but fails and returns to 700) I haven't reset the computer, just because I wanted to see if it'd go away on it's own, with the other one I put on. I'll try and attack it a little more when I get back home tomorrow. Thanks!

 

When it acts up, if you hold the gas pedal down (or twist the throttle plate on the throttle body) a little bit do the RPM’s settle down? or do they continue to bounce? If they settle down then it would point in the direction of your IAC valve or its circuit. Good luck...

 

It sort of hesitates (drops a bit then goes up) I'm thinking since the code didn't go away, something MUST be wrong in that direction. And do you think that would have anything to do with my temp sensor not working? Are the circuits in anyway connected?

 

Then that would suggest the problem is not the IAC valve or circuit. The IAC valve has no effect when the throttle is even partially open. Its sole purpose is to regulate the air going into the motor at idle to keep the idle steady. If the RPMs are bouncing when you hold the pedal down a little bit then the problem is somewhere else.


Did you clear the codes after installing the new IAC? if not, then the codes you have now may be left over from the old IAC valve. You can clear them with a scan tool or by disconnecting the negative battery cable for about 10 minutes.


I don’t know, but a lot of sensors share a common ground. The only way to know is to get the circuit diagram for your year/model ride and have a look. Good luck...

 

I had cleared the code once before, when I swapped the first IAC for the one I had laying around, and it reoccurred, then I changed the second one and left the code on to see if it would go away, since it's one of those codes that comes back relatively quick. I'll check the circuit diagram in the back of my haynes manual and see if any of those cover it. I spoke to my friend yesterday, and he's going to give me another IAC to try incase the one I just got was defective. I went to unplug the IAC and it didn't do anything, so I'm thinking wiring might be the culprit at this point since the reoccurring code says "IAC Control Circuit" - P0511