I've been fighting a problem for a long time. When the engine is cool, it stutters at startup but seems to idle just fine after 1 or 2 revolutions. The power seems to have degraded and my fuel mileage has dropped from 15/17 to 11/13. So far I have replaced plugs, wires, cap and rotor, front O2 sensor, TPS, cat, muffler, plenum gasket (oil was seeping through). I cleaned the IAC valve and port. throttle body clean. New battery. Compression measured 150psi +/-5 on all 8.
TPS 0.64V at idle, 3.72 at WOT.
MAP Sensor -Key off - 0.63V, Key OnEngineOff - 4.62V, Engine @ idle (~690RPM) 1.72 and dropped to 1.26. Seemed to vary each time I started the engine. Most measurements were below 1.5V
IAT - 8.63K ohms at 71°F, 3.73K ohms at ~ 90°F, 1.9K ohms at 190°F
ECT - 8.51K ohms at 71°F, 2.47K ohms at ~ 110°F, 953 ohms at 190°F
PCV Valve OK and cleaned up.
Hoses at EVAP canister and purge solenoid seem OK
Intake vacuum at idle 17.75 in HG cold and ~ 17in HG @ 190°F

I also hooked up a scan tool and took a whole bunch of other meausurements. It seems that my long term fuel trim starts out at -10% and gradually increases as it warms up. The data below is from a cold start to warm up condition. There was a read problem about 1-5 of the way into the readings and evertying went to zero. The rest of the data is valid.
http://i197.photobucket.com/albums/a...1_65F_Idle.jpg

 

What sparkplugs are you running? Run your gas tank alomost empty, then fill up with 93 octane and add octane boost. I have had issues with certain gas stations 87 octane after they switched to up to 10% ethanol.

 

Right now I'm running champion truck plugs but I have tried a couple different types including bosch and NGK with no changes.

I have tried octane boost a few times and it didn't seem to change anything. The problem seems to be pretty subtle but consistant. Doesn't matter what gas station I go to...

 

Maybe take your D in to have the fuel injectors cleaned? I got back 1 mpg after I got mine cleaned. Also, cold start idle is very very smooth afterwards. Maybe check the O2 sensor as well? It may be causing your D to run too rich on cold start causing the temporary fowling and also a faulty O2 can be giving you bad MPG's.

 

It is odd that you have not seen a difference with the different plugs. I saw my truck get considerably worse mileage with the Bosch platinum 4, lost 2MPG, the platinum 2 worked just fine. The NKG were better than OE but had to be replaced ever 25K. Were any of them fouled when replacing them? Also have you have replaced the ignition coil? The stock ones only are efficient until 100K

 

I am running with my original coil. I guess that could be worth a try. I want to check Fuel Pressure and timing chain slop first, though.

I didn't have any fouled plugs until my leak in the belly pan (#8 was oil fouled). All other plugs seem to be OK when pulled (not rich or lean).

 

If you have the extra $$$, I would get your fuel injectors cleaned. You can always try resetting your PCM so it can relearn everything. I had a similar problem, it was my fuel injectors and O2 sensors.

 

So I measured my fuel pressure today (after I changed oil, rotated tires, and found two transmission fluid leaks). I measured it twice. First time, I thought I saw the pressure jump around when it was priming but it happened so fast, I'm not really sure what I saw but it was 49psi while running at idle. So I shut it down and left the fuel pressure gauge hooked up and the pressure went back to zero after a few hours. The next time I started it up I was ready with the video camera. The pressure primed to 49psi and immediately drops to 47, then slowly drops to 44psi until I cranked it over. I have the video link here. You might be able to hear the condition that I'm getting at cold startup becuase it did stumble at startup. Its subtle but it did happen.

http://video.google.com/videoplay?do...4949&hl=en

I thought it was strange that my pressure went to zero. I thought maybe a bad check valve but... When I turned it off the first time, it held steady at 47psi for 30 minutes.
I also tried releaving the pressure from the pressure gauge (and caught the fuel in a bottle) while the engine was running for about 10 seconds and it didn't seem to run any different.

 

Got the tranny fluid leaks fixed (took it to the shop).
Still wondering if the FP is normal. I may have the injectors cleaned but I have tried STP injector cleaner and sea foam already and it didn't seem to change anything. I just spent my extra cash on the tranny seals. So I'll have to save up a little to try cleaning injectors...
Is there anything I can do to measure my coil strength?
Anybody else have this weird stumbling condition at startup??

 

It took me a couple of day's to think about this. I think I have it. Fuel pressure is supposed to be 54-56 LBS. I am very sure your fuel pump is gone. Also it is supposed to hold in that range too. I would definatlly replace it. It is in the tank and you have to drop it. Auto zone sells them for 189 last time I checked but on order only. You can go to checkers and they have it and tell them the price difference they will match it. It is the same pump and name brand. Call for exact pricing. There is no fuel filter. It is all in the pump. [:@]