High RPM-Low RPM

[ricksjeepster]

My truck started to show a new issue

 

when i stop in a red light does one of the next things:

 

Sometimes it accelerates like hell with no aparent cause...

and sometimes the engine begins to die almost to completely death point, but if i step hard on the brake it gets better.

my first thought was that it could be a problem with the booster but I'm no mecanic genie so i want to ask you guys who probably know better

 

Its really weird and gets me all... :wall:

 

Rick

[MJ300]

TPS?? :dunno:

[Throttle_Jockey]

If you have the 4.0 renix version I would say start with checking the intake manifold for leaks,but the high idle problem could also be caused by the idle air control (IAC) bhltaz had a really good thread on a simular problem also.

[jtdesigns]

IAC.. You should at least take it out and clean it real good.

[BLHTAZ]

IAC.. You should at least take it out and clean it real good.

:agree: Take the IAC out and clean it and the throttle body real well.

 

The "stepping on the brake" things has me thinking that there may be a vacuum leak issue somewhere though too...possibly in the booster.

[jtdesigns]

IAC.. You should at least take it out and clean it real good.

:agree: Take the IAC out and clean it and the throttle body real well.

 

The "stepping on the brake" things has me thinking that there may be a vacuum leak issue somewhere though too...possibly in the booster.

 

Thats what had me thinking it was the IAC. It basically is a controlled vacuum leak.. If it was a regular vac leak it would have a fast idle all the time. If its (IAC) is stuck shut, the loss in vac when you step on the brake will cause a higher idle.Even in a correctly working system youll get a change of idle when the brake peddle is depressed.. If the booster is leaking it would be just like any other vac leak and keep the idle high at all times. I could be wrong but thats how I see it.

[ricksjeepster]

Thanks guys

I`ll be checking on the IAC for dirt or something, this is a good point to start discarding causes of problems in the truck

Thanks again guys!!!!

 

ps

i`ll check for vaccum leaks also.. :thumbsup: