Ok I have had a problem for a while with my 4Runner running like crap. It idles bad, doesn't seem to have as much acceleration or drive as good as it used to. Every now and then it runs great. Well my gas gauge always reads lower than what there is. I noticed every time it ran better, the gauge would go up and mark what was correct. Sounds like an electrical issue.

Here is what has been done:
New Plugs
New Wires
BG Intake and fuel injector cleaning
New PCV
New fuel sending unit
New coils

I get a flashing CEL only on the highway too. Maybe the fuel sending unit isn't getting a full 12V nor the coils?

 

You should check for history codes.

 

bad ground or loose wire to to pump/sending unit.

 

grounds look good so do wires and connections to pump. codes are useless because whatever is causing it to run bad just throws a random cylinder misfire.

 

Does it only run great in certain conditions? Like when its hot and dry? Or on longer trips? Have you noticed any patterns in performance?

 

It is entirely random. At one stoplight it will idle very rough and you can see the headlights shaking. When I take off you can tell it doesn't have as much power. The next light it idles smooth and accelerates normally. The only common thing is it throws the CEL on the highway. 90% of the time it is running bad.

 

Almost sounds like a vacuum hose leak or the MAF.. although MAFs tend to cause only hesitation and I dont think a vacuum hose leak would be on and off.

A misfire usually has to do with timing.. has your timing belt been changed?

 

timing belt if fine and tight. i checked for vacuum leaks, i thought MAF too but what would that have to do with fuel gauge. What about a bad fuel pump?

 

I'd say youre at the point of taking it to a toyota dealership so they can do a full diagnostic on it..

 

Check the ground wires that are attached to the left side of the plenum

 

to me it sounds like you have a vacuum leak, i had the same problem, if you have a leak it s with all your air to fuel ratio mixture thingies hahah its verryyyyyyyy technical

 

I checked those grounds. They gave me problems one time when I loosened them to make room for the extension when doing plugs. I tried spraying carb cleaner all around to check for a leak, but with nothing. I contacted Toyota and they wanted to re-do everything I did and charge me for it. Plugs wires, injector cleaning etc etc. Sounds like they just have to go by process of elimination too. I appreciate the tips and patience guys, keem 'em coming.

 

well tell them process of elimination isn't throwing parts at it. Thats where actual DIAGNOSING comes into play. lol Could you possibly have some rodent damage to some wires? We see that quite often

 

did you have this problem before changing the spark plugs?

 

yup, it's progressively getting worse

 

I had a similar problem on my old '95...check connection from pos on battery running to bottom of fuse box (approx 12inch wire). I upgraded the the wire/connection (poor setup from factory). There is a detailed write up in the electrical threads from a similar problem

 

I checked the cables and wires to see if any are loose, corroded or gettign warm. I dunno if it is just me being paranoid but I swear I smell something burning in the cab all the time. I am going to try dropping the knee bolster and see if anything is geting hot.

 

didnt find any wires getting warm

 

okay let's run with the idea that it is occurring inside the vehicle since you think you are smelling a burning odor

Any recent car stereo activity-head unit theft, etc.? antenna change out or any subwoofers or such?

 

No, nothing new. I had a remote start put in a while back. So i checked all that wiring too since there is a mess of it. I checked everything with the truck running so i could see if it was getting hot or if moving anything around affected the way it ran.