my truck is throwing a code 13. cannot control low RPM idle or something like that.

i readjusted the idle set screw to .97 volts and the IAC was alternating between 11.47 to 9.61 Volts which should average to around 10.5 Volts. so i know those 2 are still within spec.

manifold vacuum holds at around 15 in/Hg.
idles at 850 rpms.

and the dwell is 22.6 degrees for an 8 cylinder. i have no idea what this is or what it's supposed to be at to be within specs. i'm not able to measure frequency.

 

This may seem basic but I had problem with the idle and in the end I sprayed the throttle linkage on top of the throttle body where the cables and return springs are and it solved he problem. What threw me off is that it was an intermitent problem so I started looking at evrerthing else.

 

sprayed it with what?

 

I used wd 40 and paid attention to the return spring on top of throttle body .Work the throttle open and closed as your spraying. On mine the you could see the rust coming out with the wd 40

 

you know, i do notice that the springs don't really pull the plates closed all the way. whenever the truck is idling (steady that is...) i am able to change idle (lower it) by pushing on the lever on top of the TB more closed.....does that mean the spring is bad or the plates being stuck?

also the voltage reading of the TPS doesn't readily go back to where i adjusted it previously, only until i push on the TB lever...

 

I am not exactly sure when at some point I had replaced the throttle cable from the gas pedal to the throttle body also. There also may be some binding there also that the srings cannot overcome.If there is a lot of carbon around the plates the air can slip through also.As these trucks get old it can be an accumulation of a few small things that cause the problem .It sounds like you have narrowed it down.Try by process of elimination.If you remove the throttle cable from the throttle body see whats happens. Does it snap shut? Try to narrow it down before you start spending money.

 

Did you ever get your Idle lower?
Yes it's an old thread, but relevant.

 

Hey guys this is the best forum i have found yet!!!! Ty

Ok...1989 f250, 351w, autotrans?..

Bought truk 2 yrs ago, drove 400 miles home, then used it on ranch as needed....no hiway use till now...
When i got it running again properly i had similar issues u all have mentioned...
I was chking visually every hose in engine compartment an when i tooj my hand off the vacuum cluster near distributor it was covered in black powder...
Realized this was from vac lines....
Bought new vacuum lines an replaced all of them with rubber....
Wah la!!!! Idle issues gone, truk previously was hard starting, now 2 cranks an she fires right up!!!
That took care of a lot of issues...heater weak, hard starting, trans shifting....

Just thot id put this fix in as info...

The issue i have now is when at 55mph the engine shiuld b 1800 rpms...its 2500 rpms...cant seem to get it resovled yet...

Any ideas?

Ghiaguy