Ok, here are the vitals: 2002 F150 4.6 Liter, 103,000 miles. Twice in the last week, when i put the truck in park after driving, it falls off idle. Idle drops to 400 rpm, then dies. Also, while slowing down to turn a corner, foot on brake, rpms drop to 400 rpms, then spike back up to 700. No check engine light, all other parameters seem normal.

Back at 80,000 miles, the throttle body was cleaned, egr ports were cleaned by dealer. I had a check engine light, i think it was insufficent flow to egr. After that, elbow on back of intake (pcv valve) was replaced. Have since replaced plugs and coils.

Any ideas? Kinda hard with no check light, i know. I am thinking possibly the egr again, or maybe the Idle Air Control (IAC). It's never been checked, at least by me. Haven't cleaned my air filter in awhile, but have cleaned the maf recently.

Any help? JBrew? Anyone? Bueller??

 

Could be a Fuel filter or Regulator..Change the fuel filter and test the fuel pressure - that's a cheap start.

IAC - I guess it could be, except your repoting problems when warm. - What's it act like right after a cold start ? Starts no problem, idles high, then cuts right down to 700-750 rpms ?

 

Right, cold start, it starts fine and idles right at normal, around 700 rpms. Only after it warms up, does it start getting weird, and it's intermittent, not every time.
Also, have repalced the fuel filter about 8,000 miles ago....

 

IAC

 

Check your maf, it can give you odd idle problems. If you have never replaced it, it may be time.

Also, check into replacing the fuel and pcm relays, they can act weird, even shut you down at times, or even go out completely. They are around 10 or 12 bucks, so no big money cost item at the dealership.

 

Ok, so Saturday i took off the IAC valve, throttle body and upper intake plenum and cleaned everything. The IAC was grungy inside, t.b. wasn't that bad. Assembled everythig, went for a drive, everything was great. Drove home, and it started again!! Would not idle above 400 rpms, then the check engine light popped. Went to Autozone and the code was 1507. Replaced the IAC and all is fine again... back on the road again!!

Thanks for all the help! Actually, removing and cleaning the throttle body and upper plenum wasn't nearly as difficult as i imagined. Used Deep Creep and BG-12 for the heavy stuff. The egr ports were not gunked closed, or even close to it like i thought they might be...

 

Glad you gotter fixed LD. Yea , I managed to keep my stock IAC for about 230,000 miles. There's a little trick to cleaning them. First of all , SeaFoams "Deep Creep" is perfect for maintaining as you used. - The trick is working the mechanicals inside without damaging them. I connected a heavy set of hemostats to the sensor plunger - Give both holes a good shot of B-12,Carb Cleaner, Brake Fluid or whatever I have on hand and then hit it/flush it out real quick w/compressed air, then apply Deep Creep and work the plunger carefully. Blow the initial application of DC out w/compressed air and apply again. I repeat the process of Deep Creep and working the plunger about 3 times or so. Then I scope the spring and rubber boot inside to make sure everything is still in place and that ALL carbon deposits are removed from the plunger. Also make sure it works freely.

BTW - Like I said , I replaced mine , but my old unit is still good