ToyYoda

After I replaced the cylinder head and aux. air valve I've developed a strange idle. The symptoms are, it idles like it has a cam (pretty sure it doesn't have one) but the cylinder head did come with an OEM camshaft in it. It also keeps pushing my idle adjustment valve/screw out...all the way past the rubber o-ring and it fits in there pretty snug. My compression was around 160psi. on all cylinders and there isn't any noticeable vacuum leak large enough to cause the problem and it idles where it should, only rough. My plugs were all tan and still very clean. I'm also using the recommended NGK spark plugs.

Any ideas?

abecedarian

You're saying it's vibrating pretty badly?
Ignition timing and valves adjusted properly?

ToyYoda

I've double checked both. It runs really good and the throttle is snappy like it should be. Whatever is going on is only affecting the idle. In neutral, if I rev. it up and hold the RPMs it's perfectly smooth and revs great but once it gets down to idle it shakes pretty badly. Sometimes it feels fine for a few seconds then all of a sudden...bad idle.

Kaydon

Check your MAF? Air filter?

I had a similar problem with idle, and it turned out to be a combination of a bad air filter and a loose vacuum hose.

abecedarian

Have you checked the air-flow meter and throttle position sensor?
AFM: http://www.4crawler.com/4x4/CheapTricks/AFM/index.shtml
TPS: http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml

Also you might try cleaning the intake plenum/manifold. My '91 had a rough idle and I took a can of berryman's throttle body cleaner, the spray type, and sprayed it around and down the throttle body into the manifold in short spurts while moving it around, trying to spray the whole manifold. I reconnected everything and started the engine a few times during the process so I didn't have a lot of gunk building up on top of the valves. I also sprayed a bit into each vacuum port on the throttle body and manifold- if it shot back at me, I knew the port was plugged so I cleaned it (I had 1 plugged). When I was done, the truck idled about 300-400 rpm higher than before and smoother as well. Turned the idle down and set the timing. Runs great now.

Some people use Seafoam sucked in through a vaccum hose. Same concept, I just liked the idea of being able to direct the spray with the straw where I wanted it instead of relying on vacuum to suck and splash the cleaner.

ToyYoda

It was the TPS. I unplugged it and it idled great.

pcmentor

Did you disassemble the air valve and adjust/test it?
I have been trying to figure out how it works.