No it is NOT the IAC (new IAC) causing the problem and neither is it the EGR valve I believe it is called. So basically first the truck is hard to start, which is a fuel pressure problem. Then it idles real high (2500RPM).

It's a 351w EFI with a speed density system I think (I don't see no MAF) and ran fine all winter with the IAC not plugged in.

At this time if I hit the gas the RPM's will go up then drop down to just below 1000RPM then skyrocket again. If I disconnect the IAC it will idle rough but will idle at the appropriate speed for a while then it will begin to sputter then die. At this point if I hit the gas, it bogs out.

I've spent weeks tinkering with this problem. I've pulled the codes and checked them out, but everything has checked out to be fine. I'm still thinking it some sort of input that is causing the IAC to open incorrectly but I can't trace it down. Any input would be helpful cause at this point I almost want to sell her (which I am determined not to do) and I'm stumped

On another thought, when I unplugged the IAC for the winter (because I had a high Idle) I also had the battery disconnected. Could this cause the computer to learn how to run in an improper fashion causing it to idle bad now with what is for sure a good IAC?

 

Try a new TPS (throttle position sensor).

On my F250, it did that until it got to the point it would go in to high idle on its own and then stall out at random sometimes.

The TPS and IAC work together BTW. Don't forget to unplug the battery to reset the PCM and allow it to relaeran the idle, etc.

 

I guess I'll try the battery first. I just hate to go out and start buying new parts. Maybe the ranger TPS will adapt (thats where I got the IAC) and if it changes thats my problem. I checked the resistance and such of the TPS and it checked out fine but I guess it could still be not working correctly. Hopefully I can see if the ranger TPS will fit tomorrow.

I also forgot to mention that it sputters a lot untill it warms up when I have the IAC unplugged but that might just be natural.

 

are ya sure the one ya put on is the same part #?and that it is a good one-remove the 2 hoses off the air intake at throttle body-you should see a hole for the iac-put you finger over the hole while it's idleing if it comes down to normal the iac is bad or incorrect-or so I have been told by many mechanics-hey it's worth a shot

 

The IAC is not the correct one but I know it works and it makes the truck idle the same as the one that is supposed to be on there. But I will try blocking it and see if that changes it.

 

Ok so I have re-checked the TPS and it turns out that that is sending wrong signals. Hopefully it is the problem. On dissasembly of the throttle body I found that the gasket sticks out into the path of air by about just over 1/2". Is that right? Should I cut it away and get more airflow and possibly a little more power?

 

I figured it was. Mine basically did the same thing when it went south. Now just get a manual and set-up the TPS to read proper voltage shut and wide open.

It's been so long I can't recall what it's supposed to read.

 

Yeah I got me a haynes manual a while back. 1v at idle and 5v at full open. When I get bored I crack open the manual, there really are a lot of interesting things in there.

 

cool glad ya got it fixed

 

thanks for letting us know what it was helps others down the line

 

So I replaced the TPS it now idles like a charm and until half throttle it has more, smoother power.

I still have another problem which is a hesitation at past half throttle open. Right now I have to drive it using less than half throttle or it starts to hesitate and buck. It's got a 212 code so it's a ground fault in the SPOUT circuit. It never did this before a month ago and I remember around that time I was around those wires so I probably aggravated a developing problem. The Haynes Manual is rather nondescript on how to check out this code if its not just a ground in the line but I'll figure it out sometime and report back but if anybody has anymore input I can't say no