Idle "bounce"

[mikel]

Howdy,

Just recently when I start my truck first thing in the morning it seems to crank, then catch, then miss about half a beat, and then run fine. If I plug it in at night it does not do this. It's in the 50's in the garage in the morning.

This morning it acted really weird though. It started kinda rough (as usual) and then when I dropped it in to reverse the idle started to bounce up and down. It did this for about 8-10 seconds and then smoothed out and ran OK. The "bounce" was real fast, kinda like a motorcycle bouncing off the rev limiter. It might have been a miss, but it was early and about the time my tired brain realized something wasn't quite right, it quit dooing it.

Anybody have any ideas? I'm going to check the wonderful lift pump this afternoon... I don't know if it has anything to do with this, but the EGT's have been about 100 degrees lower than normal lately. I also got the best MPG ever on my last tank.

Thanks for the help.
Mike

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'99 QC 2500 SLT Driftwood 2wd SB 24v Auto 3. 55 LSD
ISSPRO pyrometer, Walker 21468, 20,000 miles 12-19-00

-- email address removed --

Howdy Agg's!

 

[Alan Reagan]

It's not abnormal when these engines are cold for them to do this. It may be a symptom of air in the fuel system if the engine has warmed up and the idle continues to fluctuate. Last week, I changed my fuel filter, cranked up, checked everything and went for a test run. At the first stop, I noticed my tach fluctuating from normal to half way to then next point on the tach (about 60 rpms, I hate the 125 rpm increments). I checked the filter cannister and it was wet on the backside. I snugged the top dried it off, the idle settled back to normal and hasn't fluctuated since. The fuel was seeping at idle, not running out.

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2001 HO 6 spd 2500, 4. 10 LSD, Towing Package, Electric Brakes, SPA EGT/Boost Gauges, Running Boards, Fog Lights, Real Backup Lights, Running Boards