YotaTech Forums - New Engine Idle Issues

I built an engine for my truck (it was an exploded timing, old HG and head refresh job gone crazy). Anyway, new short block, new Engnbldr head and 261C cam. Cleaned and fixed up the long block. It runs OK, but the idle is particularly bad right now. I would think with the 261C that my idle would be a little rougher, but what I'm getting is really bad.

Being brand new, the HG /should/ be fine (have not checked compression, but the engine right now has about 3 hours run time and maybe 50 miles on it). The short block was factory Toyota and the head is EB's street RV. He assembled the head.

The fuel and air filters are brand new. The cap, rotor and plugs are all new. The wires are a little more than 2 years old. I cleaned the intake, it almost sparkled in there. The gaskets are all new (most everything not EB is Toyota). I adjusted the TPS, but the dashpot is removed because it wasn't operating smoothly. No trouble codes are stored and I set the idle with the diagnostic jump in place to about 10 BTDC. It seems happiest there. The injectors were cleaned by WitchHunter. He did all 4 main injectors and the cold start. The numbers for the main injectors came back good, but I didn't get an analysis of the cold start. I have adjusted the valves a few times. First was 0.008/0.012 cold when I assembled the long block. I've adjusted them twice since, both times 0.007/0.011 hot (per Ted's advice). First time I did them after the initial start they were pretty far out, the second time after a few short trips everything was pretty close.

When I first start the engine, the engine doesn't seem to want to run. It hangs out at about 400 RPM for a second and then jumps up to cold idle. It settles down nicely at cold idle. About 1500 RPM and slowly drops as the engine warms up. It runs fine, doesn't miss or anything. I goes fine from a stop, although there is a slight hesitation to rev if I tap the gas pedal. But other than that, the engine revs fine.

At warm idle is my problem. It varies between RPMs. If I set the base idle to anything near stock, say 700 or 800 RPM, the engine bounces around and vibrates like crazy. Almost like it wants to die. If I turn the idle screw out to 1000 RPM the engine is OK, although sometimes I will get the RPM bounce between 1200 and 800 RPM that indicates a high idle with the brake pedal pushed.

Any ideas? Does the dashpot need to be in place? I wonder if my throttle body butterfly is closing too much with the dashpot off. Does that make any sense? I'm at something of a loss otherwise. I have not replaced any vacuum lines yet, they were all marked when I pulled the old engine and so I didn't want to screw that up. I'm going to start replacing all those in any case.