1999 Highlander Edition 3.4 Hesitation. Stumped, please help.

[trd4runner007]

Good morning folks,

I just purchased my 5th 3rd gen 4runner. Seems that it is an affliction that I am unable to detach myself from. This particular one is a 99 Highlander Edition 4WD, E-locker with 144k on the odometer. The truck runs great and over the years we have kept it in great running shape (filters, fluids, plugs, wires, ect). Within the last 5k miles, there has been a hesitation when starting from a dead stop, or when coasting, and getting on the gas. If the gas is feathered, it is less noticeable. The truck runs great, idles fine and gets the spec'd MPG. If the truck is under any load, there is no hesitation. Replaced within the past 10k were:
plugs/wires, fuel filter, PCV, fuel regulator and o2 sensors. It does have a Stillen cat back and TRD headers, which I'm not really fond of. Does this sound like a TPS, CPS or vacuum leak? What would cause the hesitation, but allow everything else to run accordingly?

Any info would be greatly appreciated.

 

[nor_cal51501]

Good morning folks,

I just purchased my 5th 3rd gen 4runner. Seems that it is an affliction that I am unable to detach myself from. This particular one is a 99 Highlander Edition 4WD, E-locker with 144k on the odometer. The truck runs great and over the years we have kept it in great running shape (filters, fluids, plugs, wires, ect). Within the last 5k miles, there has been a hesitation when starting from a dead stop, or when coasting, and getting on the gas. If the gas is feathered, it is less noticeable. The truck runs great, idles fine and gets the spec'd MPG. If the truck is under any load, there is no hesitation. Replaced within the past 10k were:
plugs/wires, fuel filter, PCV, fuel regulator and o2 sensors. It does have a Stillen cat back and TRD headers, which I'm not really fond of. Does this sound like a TPS, CPS or vacuum leak? What would cause the hesitation, but allow everything else to run accordingly?

Any info would be greatly appreciated.

Sounds a lot like when I had a vaccum leak. Double check the intake manifold, throttle body and are all torqued properly. Also check your vaccum lines and make sure none are cracked or leaking vaccum pressure. I had a line I forgot to cap off when I installed my supercharger and it had that same bottom end hesitation then ran fine everywhere else.

 

[trd4runner007]

Excellent sir. Will do. I think that my buddy may have jostled something lose when he did the plugs a few thousand miles ago. He said since around that timeframe, it began doing this.

 

[SCRunner12]

I'd also clean the throttle body and MAF sensor if you haven't already. Might be causing some issues, but also a loose vacuum line could be the problem. I'd also check to see if your throttle cable is too loose. Might cause some of the delay.

Btw, I'll take those headers and exhaust off your hands, I mean if you don't want them and all...haha

 

[trd4runner007]

Just ordered the silicone shop set of vacuum lines from a recommended shop on this board. The OE MAF should be here tomorrow. I thought that may be the cause, but then when I thought about that it only happens when accelerating under no load and everything else runs great I was doubtful. It may be indeed, and that was the first thing I ordered. Nothing wrong with a shiny new MAF. I have never replaced vacuum lines, but I assume that it would be pretty damn straightforward.

 

[woodro]

i am also having the same hesitation with my 99 , fuel filter , plugs , wires , o2 sensors , maf and throttle body cleaning . still there ,going to also check vac lines .
if you fix it please post .

 

[SnoViking]

I had the same issue. I eventually got a PO420 code and had to replace the down stream cat. Good luck guys.

 

[trd4runner007]

So....Installed a new OE MAF and changed out most of my vacuum lines with some silicone. Hesitation seemed to have ceased. I only was able to drive it around the block several times but all seemed good. I did notice though, when backing into the driveway in reverse, the 4runner began to idle rough. I put it in neutral and drive and the idle was fine. Does it take time for the new MAF to calibrate/learn?

 

[Jasonredwood]

Maybe resetting the the EFI ECU would help at this time. Just remove the EFI fuse from the fuse box for 30 minutes.

 

[trd4runner007]

I removed the EFI fuse and all seems to be smooth. No more hesitation. Don't really know if it was indeed a vacuum leak or the MAF. I'm leaning toward vacuum leak. Anyway, thanks to those who posted. My problem seems to be remedied as of now.