ok guys i need some help here, ive got a problem getting a 500 efi with older side mount whipple to idle! when i first start the boat it will idle with NO issuses, but as soon as i give it some throttle and then back to idle it will act like its goin to stall and then idle high (1200-1500 rpms). if i shut it off and restart it, it will idle fine till i touch the throttles again.........its got me stumped ive tried a new iac valve.........i really need some help.......thanks, ted

Vacuum leak of any kind? Perhaps something being opened as it comes from pos pressure to vacuum and sticking open? Just some general ideas. Is the TB closing all the way back up?

one thing i did notice is someone had drilled a 3/8 hole in the brass filter that goes with the IAC valve! i swapped the one off the port motor and the engine idle bounced between 800-1200 rpms. i will have to check for vacuum leaks

iac sensor maybe no good,,,staying open,,, the brass filter just clean it out with break clean or take it off and see if it helps

make sure you secondary throttle plate is closed all the way

thanks for the input guys, i should proly get a merc scan tool as well, we just had both engines completly apart for blown head gaskets

could this be a TPS issue?

maybe a tps issue.


I have a side mounted blower with a bunch of pulleys if your looking for a spare blower..

You should run a seperate oil line to the blower to keep the oil cooler.

is the TPS adjustible on a side mount whipple TB?

Well guys both throttle blades are closing, I checked the voltage on the TPS its at .6v closed and 4.5v at wot, I pulled the iac off the port motor (port motor idles and runs fine). And I still can't figure out why this thing idles high. It starts and will idle until I give it some throttle and back out, then it stubles like it's goin to stall and then picks back up and idles at 1200-1300 rpms and will not idle back down. Help!!!