1990 F250 with 7.5L, auto


Stalls in N or P.
I had this problem 2 years ago. I replaced Idle Air Control Valve. Went away. Now it's back. What could it be? The TPS sensor? I pulled the codes and got
21, 10, 33 (granted the engine was cold, so it influenced the output)
I know 33 is EGR valve and 21 attributes to temp. sensor out of range, due to cold engine.

 

Id check that IAC valve again. Maybe even do a throttle body cleaning.

 

It was easy to remove and install. I haven't even driven 5,000 miles since the replacement, does it get carboned up so fast? That's impossible.

Throttle body cleaning sounds like a good idea, do you just spray carb cleaner in it, or is something else involved?

I am inclined to think it is the Throttle Position Sensor problem, but don't understand why it doesn't set a code.

 

I have been having the same problem when putting into Park or Neutral. I cleaned the IAC with carb cleaner this weekend and it seemed to help a little bit. Now instead of dying, it surges where it will almost die, then come back, and surge again. I was also thinking the TPS. Other than putting in park or neutral she is running fine. Any help to fix this would really be appreciated! Should I replace the IAC?
Thanks,
Matt

 

I believe that if you put it into Park and Nuetral, the engine is supposed to rev a little for a quick second. Not sure what makes it do that though.

As far as the TB cleaning, this is what I suggest. Buy a couple cans of Seafoam. Its about 5 bucks a pop but well worth it. I submerged my whole throttle body into it(IAC sensor and all... its electronic safe) and then let it sit for bout 15 minutes. Came back out with an old toothbrush and pulled the throttle body out of the seafoam. More than 80% of the carbon on the inside of the TB was gone. I used the brush to kinda scrape away what little was left.

Once you put it all back together, pull the brake booster vaccum line and pour about 1/3 to a half can into it slowly, and make sure you keep it at a high idle, like 1500 RPM or so. Now someone correct me if I'm wrong, but arent you supposed to shut it off, and then dump a little more into there? And then about 10 minutes later come back and start it up? This is what I did to mine, and it seemed to help. Note that you will have more exhaust smoke than a cummins on a -20 degree mornin tryin to run 2500 RPM. Its bad. Make sure your area is well ventilated. Run it for a few more minutes and the smoke should clear. Hope this helps.