1998 F150 4.6 standard. Idles high 1100-1400rpm when warm. When cold it idles at 1100-1300 rpm, and begins to idle down to 800 rpm. When driven to normal operating tempurature, it idles high, and sometimes it will come down. Replaced IAC, TPS, smoke tested (without any leaks). When I pull the connector from the IAC, it idles down to 650-700. What next? I've been searching the net without any other leads. Any suggestions would be appreciated.

 

Sounds just like mine did before I adjusted the blade on the throttlebody. You also may want to look at doing the beer can mod.

 

Two issues come to mind on this. The first, less likely, and the cheapest to fix is the PCV valve and the hose that is attached to it. If the hose is leaking air, it should be replaced. Replacing the PCV is you haven't done so recently as this only cost about $3.

The second is the throttle position sensor (TPS) if this is giving a bad reading to the PCM the PCM will send the wrong air/fuel mixture to your engine and could be the cause of your problem. Before changing this, however, you should pull your engine codes. Codes P0122 and P0123 indicate a TPS problem.

 

ghostrider, thanks for the reply. I did adjust the blade and it idled down. I did a road test with it, and so far so good. I'll do a search for the beer can mod, sounds intriguing. I'l keep you posted.

 

Not a problem, you also may want to check to make sure that your tps voltage is at 0.99 volts closed.

The beer can mod is cutting up a beer can the same shape of the iac valve and putting holes about half the size of the iac to help control the amount air that the iac valve lets in at idle.