I just purchased a 1990 F150 supercab 4X4 with 64,000 miles, 5.0 liter and auto trans. Question is this; starts fine but idles fast. Runs well with plenty of power (slight miss at idle and steady speed) I changed air filter as the one that was in it was full of oil from blow-back. As I was looking over the engine I noticed that the IAC was totally missing. Any ideas why someone would remove it?

 

People do strange things when they don't understand how something works.

 

I just hope when I put a new on it will fix my idle problems

 

don't get one at autozone.

 

Yes your idle will certainly drop, it may expose the real problem the PO was trying to fix when he removed the IAC however. You can claim a higher IQ than him if you pull the codes to see what the computer has to say about it before trying to blindly fix the problem.

 

Thanks, that I will do. Hopefully I can get the codes pulled this weekend. I will let you know how it turns out.

 

Where should I get one quicklook? I need one also...

 

I installed a new IAC and it made no difference at all. Well it actually made it idle faster especially when cold. I disconnected the battery to reset the computer and drove it around to let the computer catch up with the change. I then pulled the codes and all I can get is a 22 and a 33 code. Any ideas?

 

Code 22= BP sensor or MAP out of range

Code 33= EGR valve opening not detected

 

Your truck has a MAP sensor up on the firewall, Ford Fuel Injection Manifold Absolute Pressure Sensor (MAP), try replacing it with another.. even a used one if possible. Make sure the vacuum line is attached.
EGR problems are common, you may want to remove yours and ensure the valve isn't stuck open and that the position sensor works as it should. Ford Fuel Injection EGR Valve Position sensor (EVP)

Your motor has a large vacuum leak if the idle is high and uncontrolled, or the TPS could be bad, or the throttle adjustment screw has been changed and the butterflies are actually open too much.

 

Actually the arm does not touch the adjustment screw. If I push the mechanism towards the idle screw the idle speed does come down but not enough. I took apart the egr valve sensor and cleaned all the connections. Same with the MAP sensor. No change

 

Check the voltages at the TPS and try to set the stop screw to obtain the voltages shown here... Ford Fuel Injection Throttle Position Sensor (TPS), closed throttle about 0.75v, WOT at 4.5v, and no glitches or flat spots in between. If this checks out start looking for a major gasket or vacuum leak.

 

I will do, I'll keep you posted. Thanks

 

Put in a new MAP sensor still did not correct the problem. Only code I am now getting is 33 dealing with the EGR valve and I know that is not keeping my idle up over 1100 rpms. I have checked and rechecked for vacum and air leaks and have totally come up empty. Need some ideas as where to start and what to look for from this point foward. I am going to pull the TPS and check it out tomorrrow. Thanks

 

Unclear whether you just cleaned up the EGR sensor, or the valve too. If the EGR valve is stuck open, that will cause a high idle as well.

I had a similar problem on my 93 when I got it, the mechanism wasn't touching the stop screw. I ended up cleaning the throttle body passages, and the rotating mechanism. Oiled it up good, and it seems to be fine now.