Engine compression

[SoCalSlaughter]

I have a 90' Chevy Suburban V2500 5.7lt TH400 trans. Ive noticed recently a miss while the truck is at idle in park, once its warmed up it seems to go away. I tried to do a compression test but the starter went out.. haha replaced starter last night and havent tried a test again. I tried on cylinder number 2 hooking up my compression tester with my air compressor plugged into it and at tdc and btc I can hear a hiss coming from the exhaust and I rock the rocker arms back and forth making sure they are loose and not pushing down on the valve. Could this be a burned exhaust valve or rocker arm to tight? I did noticed the rocker on the exhaust didnt move as much as the intake valve. Valve job in my future? haha

[68gmsee]

The miss at idle, if it's slight, can be caused by several things. It may be ingnition like plugs, cables, distributor cap, rotor. Could be a vacuum leak or even exhaust leak. A compression test can help to determine the overall condition of rings and valves but a leak down test as you did on the one cylinder would be a better indicator.

You don't mention the mileage but I wouldn't tear into it before replacing and/or checking the easy stuff first.

[Rufton]

Spark plug will often tell on bad cylinder.
The misfiring plug may have more deposits than healthy cylinder's plug.

RA wiggle test is inconsistent w/ hydraulic valves because unknown bleed down.

I would adjust lifters again to be sure.

[SoCalSlaughter]

The motor has158k miles on it, ive owned thr truck since 113k miles, always kept up on service. But pulled spark plugs and all have good wear on one, noone of them stuck out to me more then another. And i dont think the valves have ever been adjusted. And it does have newer accel dis cap/rotor, accel 8.8 wires, ac delco spark plugs at .45 gap, i did recently put a edlebrock preformer intake manifold on it with stock intake gaskets, but i was also told that was ok. I also have a msd ignition coil its about 4 years old, if it matters
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[68gmsee]

Mileage is not too high for a 90 but never know. I guess the next question would be, when did it start missing? Was it after a parts replacement or did it gradually creep up on you?

Just as an fyi: Few years ago I had a slight miss also noticeable at idle in my 68. I had done a tune up a few months before with new ignition components. I still had my old plugs so I started swapping one at a time until I found the culprit. It was one of the new Autolite plugs I had bought a few months before.

Another engine I have is a 350 on a stand. It also missed at idle and found out it was a combination of timing and idle air adjustments.

[SoCalSlaughter]

Well, I ran Seafoam threw the motor, advanced the timing and the miss is gone. She runs alot better, has more pep. Only thing is when its set at 0 degrees it runs rough, I advanced to 4, ran better, advanced to 8 and runs awesome now.