my neighbor just did a lot of work to his truck and he is having some problems the shop cant seem to figure out. When sitting at a light the truck idles up and down (fluttering a little). The tachometer doesnt read below 2300 rpms but reads fine over that. He replaced the cluster in the dash and still has the problem. He said it feels like it is missing when sitting but runs fine under load. Any ideas guys?

 

Maybe find out what work has been done to narrow down the problem

 

new heads. new bottom end 1 year ago good compression after new heads installed.

 

id look for a vacuum leak somewhere, first. Hooked it up to a scanner? Has he checked the TPS voltage?

 

I am thinking computer problem. He is on his second one and things dont add up on his story. Will a bronco 5.0 computer for the same year work on a 2wd truck?

 

Being they done a lot of work, be sure all the ground straps are back in place

 

Bad MAP sensor can cause the idleing issue,.. as can vacuum leaks. But the tach not reading below 2300 RPM would lead me to seek out a bad ground on the coil or possibly the module on the distributor going bad.

4x2 and 4x4 should use the same computer. Both are air density motors. The only difference in computers for the trucks that I can think of would be 351 vs 302. But either should run the truck fine. If the computer went bad it shouldnt be running at all. The ECM relay needs to trigger fuel pump relay. If bad,.. the fuel pump wont come on.

Hurst

 

thanks hurst gonna try your way before the new computer.

 

also check the IAC (idle air control)