Truck is a '99 4Runner with the 3.4 and 190K.

My idle is rough, although it stays within spec (~700 RPMs) most of the time. Acceleration is also very slow, and the engine feels completely gutless. My mechanic checked the fuel trim and said everything looked okay. I'm not sure if this completely rules out a vac leak, so I've replaced a few hoses that looked worn. I can't find any obvious cracks/leaks though.

I also pulled the throttle body to give it a good cleaning. I'm not getting a CEL so I'm really lost on this issue.

Any help? Thanks guys.

 

bad spark plug wires or plugs ? maybe a coil pack ?

 

plugs and wires were replaced recently (within 10K miles).

I haven't checked the coil packs, but it seems like they would trigger the CEL, no?

 

Easy way to check for vac leak-- get a can of starting fluid and spot spray around all of the hoses. If you get an area that you spray and the idle smooths out-that would be a leak.

 

Try this: hook a vacuum guage up to intake vacuum. The needle should be steady (17-22 inches), and return instantly after revving. Low readings, jumping/fluctuation, vibration, regular drops, low fluctuation, or slow return will help you diagnose things such has vacuum leaks, leaking valves, ignition problems, worn valve guides, compression or blown head gasket, clogged pcv, clogged exhaust (ie bad cat), etc...to name a few.

Its easy and takes less than 2 minutes

 

check out this link: http://autospeed.co.nz/cms/title_Usi...3/article.html

 

what brand of wires and plug did you use ?

 

rob, cpate - thanks for the suggestions on checking for vac leaks

elton - i used OEM NGK plugs (dual electrode) and NGK wires

 

Do you know of a good place to hook up the gauge on our trucks?

 

I also have this same problem, 97 4runner, 3.4L about the last 5 months my 4runner has ran rough intermittently only after a warm startup though. Seems to becoming more of an issue lately. Cold startup it runs great and accelerates as normal. But upon restart it runs really rough and acceleration acts as if its missing spark, low fuel pressure or possibly too much fuel. No fuel smell is present at anytime. After about 10 minutes of run time it seems the computer compensates for the poor idle then it runs great! Idle at operating temperature is usually about 800rpm and at opp temp during rough idle its about 700rpm steady, but doesn't bounce up or down on the tachometer. I have replaced many parts trying to find the cause of this. Replaced all plugs, wires, fuel pump/filter, timing belt assembly and the #1 coil pack. All parts used are OEM dealer. Checked and double checked for vacume leaks and none detected. Anyone have suggestions before a replace the last 2 coil packs and replace injectors? Would cleaning the MAFS possible solve this issue or would the MAFS ever even show symptoms like this? I am leaning more towards the last 2 coil packs causing this. Is there a way to test coil packs while its running poor and then when its running good? Can coil packs discharge intermittently makin it run good on initial startup and poor after restart? I appreciate any help or suggestions on this issue. Thank you.

 

This is a long shot but it could be a broken thermostat. Had a similar problem years back with my wife's minivan. Ran fine when it was cold then ran like crap once it got up to temp. It was the thermostat and a new one fixed the problem.

 

I know when this happened to me, it was because of low compression in cylinder 3. It was very slow to acceleraccelerate and I didn't feel the rough idle until about 800-700 rpm's. It doesn't hurt to compression test, and get to cross that off your list of things it could be or find out the cause.