hotrod351

about 4 years ago i turned up the idle on my 90 4.9, using the adjustment screw on the throttle body because it didnt seem to want to idle good. anyway i checked it yesterday and its 1.077, book says .5 - 1, when i adjust it to that it will idle when completely warm but not untill then and yes the IAC is new and working. guess im not hurting anything by doing this.

Good old Bill

Back off the idle screw so engine idles 400-500 with the IAC disconnected, that screw is only there to prevent binding of the throttly plate and housing bore. The IAC takes over from there. You just might find the TPS voltage back in range.

hotrod351

did that but still out of range. should i elongate the holes, the book says that the 4.9 doesnt, or cant, be adjusted.

Good old Bill

When the TPS is unbolted is the voltage within range? If so, what is preventing if from getting lower? Nothing---then I guess elongating the holes is in order.

hotrod351

what is preventing it is the fact that i had to turn the throttle plate adjuster screw in to make it get the right idle.

Good old Bill

OK, as hard as it seems to accept, something else is wrong with the truck, If the engine only idles on the screw, then there something not getting enterred into the PCM for it to make the adjustment as necessary thru the IAC. If it has an IAC, idle is controlled by it. What codes are you getting? Is compression even?

hotrod351

havent checked compression but runs good and after warmed up idles perfect. has a slight surging around 45 mph. i just changed the intake/exhaust manifold gaskets, had a vacuum leak and mech. friend told me that more than likely it was a intake leak. besides the valve cover gasket had been leaking for years so the intake had to come off anyways, also changed the injector orings. funny that after i put it all back together it started right up and high idled perfect, the first time that is. the first code i had was 32 or 33, cant remember, but it was for the EGR, the vacuum line had been popping off it for years so i put a hose clamp on it, even though i checked it with a vacuum pump and it held i was told it was building pressure and making the hose pop off. hasnt done it since i changed it. now i get a code 22 = MAP but checked it for the 5 volts and it has it, also changed it. after changing it my gas mileage went up some and seem to run better. the only problem now is the hard start and slight surge at 45 mph. it has always started a litle hard since i got the truck, about 5 years ago. would start then stumble and die then restart and sdle perfect. i think its something minor but havent been able to find it.

hotrod351

has nay one elongated the holes in the tps sensor so they could set it at 1.0 volts to see if it made a difference. im talking about one that say is at .85 or .90, ive done some reading about getting it closer, say .99 and it seems to have made a difference in starting and cruising. i dont know why ford decided to make the 4.9 non adjustable. from what i understand 1/4 of a volt makes a big difference.