just recently my truck has been acting crazy, whenever i hit the gas and then i tap the brake like going to drive through window to drive thru window my truck will bog down enough to almost kill itself and sometime it will, anyone know what might cause this?

 

You need to post some information about your truck. Year/engine/style/transmission?

 

first guess would be vacuum leak, could be at the brake booster.

 

My 94 F150 use to do the same thing and it was the idle air bypass valve.

 

Bug has good start with Idle Air Bypass (is also called IAC by some..maybe different per year) / also good to check for any vacuum leak/ good to check & change your air filter if you haven't in a while. It's likely something in or around or leading to the throttle body.

good luck and remember Idle problems are rarely the first thing you check or try unless its an obvious cracked vacuum line.

 

Sounds like my 88 last week. I would start mine and it would hold a high idle. Then once it went in the warm/low idle it would surge. I could drive it but once I stoped it would stall. Idle Control Valve. Looks like a small motor by teh butterflys on the TB. You can try cleanning it up a bit. I cleanned mine and its running great.

 

its a91 f-150, 5.0 e4od 4x4, just had all the vaccum hoses and iac motor replaced maybe i pulled off a hose the other day when i was changing plugs and wires

 

look for any hoses that didn't get replaced, there might be a couple of small ones that got brittle. Also probably already done so but while you're in there double check all the plug wire connections are clamped on good. I had a #7 that wasn't seated good a long time ago and gave me similar problems. weird that it would fire at all and only miss sometimes. I guess the metal parts were touching enough to give me intermittent plug firing.

I'm sure you did it right but my book says improperly gapped plugs could cause rough idle. I doubt that's the cause. I just changed mine out and out of the box was pretty close to .044 gaps.

Good luck and keep running it to ground. Give us a post when you find and fix the culprit.

 

it was a bad IAC motor i took it back and got a replacement and now its running better than before