Help me create the "Surging Idle Checklist"

Why isn't this thread a sticky anymore?

I'm gonna go out on a limb here, and sound stupid for a minute. is the IAC and IAB the exact same part? All through these posts I've heard people referring to cleaning the IAC in one post and cleaning the IAB in another post, one person saying the IAC is the thing on the front of throttle body with wires, and the picture labeling that same part as IAB. So, yeah I'm a little confused.

Zak

From my original post at:
http://forums.stangnet.com/showthread.php?t=736443

zlyles said:

I have an 89 5.0. Up till recently it ran and idled great. It still idles great. My problem is, once it warms up, sometimes it will stall every time you take your foot off the gas. I can crank it right back up no problem as long as my foot is on the gas while cranking, and it will stall out again, OR I will rev it as it tries to stall, and it will idle at about 1500 RPM's for about 10 seconds and then stall all over again. If i start driving it's just fine, and the very next light i stop at, it will idle perfectly. Sometimes while driving my check engine light will flick on for a second and turn off, however, when it was hooked up to a scanner, it showed no error codes, I even ran it long enough for the light to flicker and it still gave no codes.

Any ideas?

Thanks,

Zak

Click to expand...

After being directed here by jrichker, I went through about 7 of the steps, at which point i got bored and went to something else... my hideous cooling fan wiring harness. This consisted of a generic fan wiring harness from advance auto, and an additional 5 prong relay. Being as I have a 2 speed fan from the late model 4.6L, it was running low speed based on the thermometer lodged in the radiator fins, and flipping on high speed with the A/C. Wires were all over the place, and ugly colors too, so I did some cleanup work and also wanted my low speed to run constantly when engine is on. I ripped out the harness and wired my own setup with two 5 prong relays. I was able to unscrew the ground screw for my high speed relay by hand with a socket. After the rewire, my car has not stalled once while running with or without the A/C on. Apparently the sloppy ground for my A/C relay was the cause.

I still have a problem I've had pretty much since I bought the car. Very frequently after the car warms up, I can turn it off, and when I crank it back up it has idle problems and will stall. After I re-crank, and give it gas for a bit(10-15 seconds) the idle will smooth out and run on it's own. Any ideas? I've already cleaned my TB, IAC, MAF, Air Filter, replaced fuel filter, and I'm about to go pick up a brand new IAC from the dealership.

Thanks,

Zak

Mine surges bad too, Mine is a S/C car. Since I installed the S/C it doesnt want to idle It will idle like at 500 RPMS till either I rev it up and it will hang up there for a few seconds and then fall and die OR it will idle at 500 then die either way DIES any suggestions, I read the list and the only thing I havent tried is the elbow that goes to the S/C but I have a power pipe that replaces that elbow

jrichker said:

Try clocking the MAF (rotating the MAF housing). Sometimes that helps place the MAF sensor inlet in smoother flowing air so that it gets better airflow and makes more accurate readings.

Click to expand...

ok I will try that...also the car just started poping at idle every few seconds , sounds like in the exhaust, could this be the culprit of the idle or is it running lean at idle

bump

I have a surging idle for the first two minutes when the engine is cold. (No surge in temps above 80) Had that since buying the car.
From your list, the only steps that list cold idle problems are the IAC and base timing. Are there any other things I am missing in regards to a cold idle only? I have an F cam and I'm starting to think it may be a rich/lean condition that may need a tune for open loop.
(BTW new IAC, air/water temp sensors, and 12* timing, some backfiring into the intake under load only if engine very cold)

Thanks for this thread Jrichker

If your having crazy issues with your throttle sticking or idle staying higher than what it's set at, try loosening the 2 TPS screws a little.
EDIT: maybe that wasn't my entire fix! also check your throttle plate screws to make sure they haven't loosened and when you tighten them MAKE SURE your throttle blade is not binding with the throttle bore!

History: I have been hunting down my intermitent sticky throttle/high idle problem for about a month now, since I bought the car. The car seemed alright but ran very rich. Thanks to this forum I figured out how to dump the codes and found out that I needed a to adjust the TPS because it was out of range. It first measured .002. I did some adjustments but could only get it to .68 even after widening the holes with the dremel. That's when it started: intermitent sticky throttle/high idle (what I mean by this is RPM's would stay at the RPM it was when I pushed in the clutch or drop very slowly, put it in gear and the car would increase speed with out me touching the gas, idle wouldn't return to to base while stopped at a light - sometimes 1200/ most of the time 1800, seemed like the idle was possesed and did what ever it wanted to). I would try different things: clean TB, IAC, MAF, Filter, new TPS and kept checking range after I did different things, base idle adjustments, even found 2 vacuum leaks - one on a broken vacuum cap and another on the bypass tube for the supercharger (boost is great now!) All these things seemed to help a little but the problem would keep coming back, sometimes better sometimes worse. Codes were always: 15 - SCT chip causes this, 85 - CANP not connected/ smog removed, 95 = Fuel pump briefly lost power or something like that.

I was reseting the base idle at 900 and after I did I readjusted the TPS, disconnected the battery and reconnected the IAC. When I started the car back up I let it idle for about 2 minutes to start relearning and the idle wouldn't drop below 1200. Maybe it just needed more time to learn -so I went out for a little ride. It was a little better but still wasn't right. When I got home I grabbed the throttle linkage with my hand and could slightly move it back - idle would drop right back to 900. Flipped the throttle and again it stuck around 1200 and would not drop on its own. Something had to be sticking! WTF!! I've already rerouted the throttle cable, checked the throttle plate when I was cleaning it, everything! I loosened the 2 TPS screws a quarter turn thinking maybe they are binding the throttle plate and the idle went right back to base idle. Flicked the throttle and right back to base idle. Took it out for a ride - perfect! Maybe the aftermarket TPS's are a little bigger than factory?