High Idle issues in Park/Neutral when warm

[Haus]

1992 5.0. Mostly stock besides the usual parts I had to replace

I went through the entire Idle/Surge Check List and still cant get rid of this High Idle.

I replaced the IAC, MAF sensor, TPS and checked for the 5 vref.. I only get codes 41/91 for KOEO and KOER but I always had those codes even with new O2 sensors but and it never did this before. I cleaned the Salt/Pepper shakers. Checked for and fixed vac. leaks. I installed a new walbro 155lph FP. Pressure is at 41 with vacuum disconnected. I cleaned the ACT and ECT. PCV is still good. I never touched the timing. Got it checked and it is at 10 degrees.

When the car is cold it idles a little high for my liking. little less the 1000 RPM park/Neutral but I can deal. but when the car warms up and I put it in park after driving, the RPMs idle at like 1500. but ONLY when the car is warm/hot and ONLY in park and neutral. in gear it idles at a little less than 1000 RPM.

I tried lowering the Idle with the screw but even with the blade closed completely the idle is still high. It wont come down at all.

 

[Mustang5L5]

When you adjust the idle with the screw, do you reset the computer?


Anytime you adjust the idle screw, you must unplug the IAC and pull the SPOUT connector out. This locks timing and disables the IAC. Set your idle down to 600-800RPM and then unplug the battery for 30 mins to reset the computer.

Hook everything back up, verify TPS voltage is between 0.5-1.1V (if it's a Ford TPS it should be, aftermarket might require adjustment to the 0.5-1.1 range....you don't need to do that 0.99v BS..all a myth)

Restart car and let idle for 2 mins, and then 2 mins with all accessories on.


If you try to back the idle screw down, all it does it cause the IAC to open more. Usually if you start messing with the TPS and IAC and idle screw without a reset, it causes high idle issues.

I suggest fixing the 91/41 codes as well. Usually when both are on it could be a wiring issue or a large vac leak. Could affect your fuel economy

 

[Haus]

I cant get the idle down at all. with the IAC disconnected and the spout removed it still idles at 1000 rpm even with the throttle blade closed completely. This ONLY happens when its been running for a while. The hotter it is, the rpms go up more

and the temp gauge is going higher. even after driving for a while before this idle issue it would rarely go beyond the 2nd line(1st being the 130 line). Now its going up wards to the middle but still in normal range according to the stock gauge.

and i think the 41/91 is a fuel issue for me. Goes away when the FP is increased a bit by removing the line to the FP reg. and capping the line

but the car it self drives great

 

[Haus]

i was kinda thinking a bad thermostat. I never replaced it since i owned the car in 2004. Since the car is getting hotter quicker then it used to and now have this idle issue.

 

[Haus]

I upped the FP and drove around for a while

now on KOEO I get 11

KOER I Just get 13

Now im thinking I got the wrong IAC. I should of known cause I had to mount it upside down cause of how the connector comes straight out in stead of bent cause of the air tube. but the whole thing bolts up fine minus the fact i have to bolt it upside down.