So to check if the brake booster is leaking vacuum then I should just disconnect the vacuum line and plug the line correct? Also to keep the thread on track, I understand that ford efi's never had good mpg but really 6-7mpg is insane not to mention the fact that my truck acts like a top fuel funny car at a stop light is the real issue. And I love my trucks and never complain about fuel mileage! But like I said earlier my 82 F250 with 4:10 gears at 3200rpm and 60 mph got close to 14 on the highway!

 

My mom went through 2 IAC valves before hers idled right but mine is different since her rpms were all over the place. So should I remove the IAC and throttle bodies and clean them up, or should I just buy a new IAC and what else could I check or look for.

 

the whole throttle body is dirty and needs cleaned !!

 

Ok so an update with no change in idle! I have cleaned the TB, IAC has been cleaned and check for voltage as well as resistance, I have check the EGR valve pressure sensor for the same, The EGR valve has been cleaned as well. Timing has been checked, Fuel pressure was 32 with the vaccuum and 40 w/o. Vaccuum pressure on the manifold was 20psi. I have used 2 can of carb cleanner around the intake looking for vaccuum leaks and still nothing. I do notice that the truck seems to be worse at a stop with brake pressure applied, the longer I sit at a light the more it shakes and stumbles! I was reading in my haynes manual that the BOO switch will cause idle issues it there is a burned out brake light! My third brake light is burned out! I can see how this would effect the idle at a stop but not while I am working on the truck with the truck in park! so maybe there is 2 issues! I am going to try and replace all the vaccuum lines with new hoses and connectors and see if anything gets better, but my fuel mileage is getting worse, I am now sitting at 103 with less than a 1/4 tank on the rear tank! I will be doing a compression ck hopefully this weekend, but I am praying its not a bad head gasket! I am just at a loss and cant figure this thing out! Help!

 

if you have done every thing else then think about changing injectors !

 

Well the injectors seem to be clicking, but just to see I pulled the fuel rail on the driver side and removed the #5 injector and checked to see if it was working and then used some compressed air to shoot through it, that one looked pretty good and I also check out my tps tonight and it was spot on per the haynes manual. I did find that my IAC is being weird, when I unplug it the idle never changes, so i will pick up one of those tomorrow from advance, but I did check resistance and it was good however the voltage is what stumped me. When the key is on, engine off the manual says that there should be 10.5v however I am only getting .25v, but if the engine is running then I get around 12-14v. Of all the searching on the web I can not find anything that verifies this!

 

yea thats what i mean but no matter what, an old ford truck aint gettin 20 mpg steady. maybe with the proper gearing and setup you can get close, but then its not a truck anymore, its a gas savin, geared up grocery getter with a bed imo

 

Well I changed out the IAC and with non avail! Its still didn't fix the problem. I am lean more towards the ECU is bad. When I installed the new IAC and then disconnected the connector and there was no difference in RPM changes. I also check the voltage at the connector and still got .23v, the haynes manual says I should get 10.5v with the key on engine off, I do get that however if I ground out the neg lead on my multimeter. So I am thinking that the ECM is not closing the ground on that wire. I have even tried checking voltage at the EMC pins with no change! Anyone got any ideas. Also I am planing on getting a used ECM is there anything I should look for and I should just be able to match up part#'s on the ECM's right?

 

Ok so I redid the voltage check and got 10.5 on the initial key turn when the ecu is energized and found that my old IAC was stuck closed and the spring wasn't helping it stay open, so I just put the new one on. Of course it did not change that my truck is idling rough, I sprayed another can of carb cleaner around the engine for a vacuum leak but still no luck. I am just going to replace all the plastic lines with all rubber hoses just to rule things out. Also pulled all the plugs and the look like they did when I replaced them! I did notice that the green hose that goes to the EGR valve has a small amount of vacuum, I didn't think there was supposed to be any vacuum there at idle. And when I shut the truck off, I noticed that the EVP solenoid was making a purging sound, is that normal, voltage and resistance was good at the EVP.

 

You said you shot air through the injector when you had the rail off. If you didn't apply voltage to open the injector and it still let air through then that injector is stuck open or leaking.

 

Yeah, we used an electric source to open and close the injector. But we only checked out one injector, they looked fairly new so we didn't mess with rest. but if I have to redone intake gaskets or head gaskets I am going to get a new set.

 

compression check should've let you know about hg. any big variance between cylinders?

 

Havent gotten around to do the compression check hopefully I will be able to do it this week.

 

Take the large tube off the bottom of the EGR valve and drop a penny in the the tube and screw it back on just snug and see what the idle dose.
Also check the PCV valve and see if it and its vacuum hose are OK.
Your engine should die when you unplug the IAC valve.

 

Did the penny trick and no idle changes, what does this mean?