bryonb

I'm having problems setting my idle. Truck will only idle smooth if its set around 1000 RPM. I have one turn of the screw left to adjust down the idle. Then the screw bottoms out at 750-800 RPM but its a rough idle.
I've cleaned the throttle body,plenum,cold start injector, air filter,vacume lines. Has a new thermostat. The AMF is clean and the door moves freely.
I just swapped out the old style intake for a 92 intake but this problem was present before the swap. I was hopeing the swap would fix it. Also got rid of the EGR system and blocked it off with the LC Eng. kit. I'm wondering if theres a sensor or something I'm overlooking.

Appreciate any help

toyota4x4907

Do a tune-up: Spark plugs, wires, cap and rotor, oil change and coolant flush.

check for any vacuum leaks around the throttle body and intake.

bryonb

Just changed coolant. Plugs wires were done not so long ago. Set timing.

toyota4x4907

Well you didnt say you did those in your first post

Did the rought idle happen before or after you changed plugs, etc.?

bryonb

After. I also put a new O2 sensor.

toyota4x4907

Try different plugs and wires (NGK or Denso). Same with the o2 sensor.

abecedarian

hmm AMF... they make good bowling balls.

you readjust the timing when you lower the idle, right?

abecedarian

oh, and if you have to bottom out the screw to get the idle RPM down to 750...
you likely have a vacuum leak or a bad idle air control valve under the throttle body... either or.
turning the screw all the way in would most likely result (if everything else is perfect) a stumbling idle at around 450 or the engine dies.

abecedarian

maybe I shouldn't rule out a stuck PCV valve or an issue with the brake booster either... but....

abecedarian

then again, maybe I shouldn't rule out the dashpot or the throttle plate stop screw either.

Joe's Toy

Ok guys I know I'm bringing back a old thread but i was just wondering if the op ever found a solution? Please allow me to explain my problems a little more.

I've been chasing idle issues with my truck since the pay time I changed my air filter. Thanks to a helpful yota-techer I found a crack in the intake hose. The truck idled fine for about a month then the idle slowly has dropped to around 500 very rough rpms. So I screwed the "idle adjustment screw" out to the point where it vibrates loose and the truck still seams to reset back down to 500.

I've replaced the tps (and adjusted it) and most recently put a high output alternator on due to my old one failing.

Currently I have the screw that adjusts against the dash pot screwed in so my truck doesn't just stall at red lights but my now it idles crappy when it's cold and at 1100 when it's warm. Other then a air leak is there something else I should look for? The dash pot doesn't move. Is that right?

hrt4me

what was your specific procedure for cleaning each of those items?