vibration @ cold startup

[chessy56]

LB7, 400K miles, just had head gaskets and fuel pressure regulator replaced. I've noted that startup with a cold engine (~35 deg F and colder) leaves a noticeable engine vibration until the engine warms up a bit. Adding throttle during cold idle eliminates the vibration. I've also noticed that I have to crank a bit longer before the engine starts up- unless it's been plugged in for a while beforehand. No codes for glow plug failure, but I did notice a code for a fuel temperature abnormality that I haven't seen before.

Maybe I'm experiencing something abnormal with the newly replaced pressure regulator- don't know. Any thoughts would be appreciated. Thanks again.

[rapidoxidationman]

My first thought, before reading all the way through your post, was that you've got a glow plug or two on their way out.

Given that you've JUST had the HG's and FPR done, I'd go talk to the folks that did the work and get their take on it before even touching anything.

Edited to add: Did they change out any of the plugs? I've had inferior ones before, and it was truly noticeable that they were inferior - exactly the symptoms you describe. You shouldn't need to plug in until 20 below zero F, and even then the engine should start cold. Is it possible that they didn't plug a coolant temp sensor back in (or maybe shorted out the sensor)? There's a lot of plumbing and wires to back out of on a HG job...

[DmaxMaverick]

Simply, it sounds like injector(s). What you are seeing/hearing may be the imbalance before the cylinder balancing begins (125-140F ECT). Once it smooths out, apply slight throttle (while in P), just enough and just below it increases RPM (1% throttle). Or, if you are parked on an incline, select N and let it roll to 2+ MPH, with no throttle, or the same in D if on level ground. The balancing should disengage, and the rough idle should return, if it is the injector imbalance. This may or may not be an indicator of a problem. If it balances and doesn't knock or smoke, it's unlikely to be a problem.

Glow plug issues will disappear within seconds of a cold start.

[chessy56]

I've tried the 1 degree throttle trick after the engine had warmed up. I don't feel any vibration worth noting. Balance rates range from +2.5 to -2.5 on a couple of cylinders- others range between +/- 1.0 and no smoke. One glow plug was replaced during the H.G. job. Perhaps just something different- I can wait to see if anything becomes of it.