Chevy truck tacometer dancing on startup

Hi, I have a 96 silverado and when i start my engine my rpms start out real low around 400 then jump up to about 1000 then drop to a sputter then shoot back up to about 1200 and then slowly fall back down to 800, my normal idle rpm. This all happens in about 5 or 6 seconds. After the rpms settle down it usually runs runs and accelerates fine. Startup is my only problem. Sometimes the truck starts right up when I crank it and sometimes it takes up to 3 cranks to start. Ive replaced the coil and had the ignition module tested. Spark plugs and wires are in good shape and I've completely cleaned the distributor. I tried letting the fuel pump run for a few seconds before starting and it made no difference so I don't think its a pressure problem. Ive done pretty much everything I know to do on my own. Any suggestions? thank you ive red your post.
what exactly is the problem?
are you having trouble starting the car? or, is the speedometer giving you trouble ?? sometimes the truck starts right up and sometimes it has to be cranked up to 3 times until it starts. and when it does the rpms of the engine fluctuate for a few seconds then it settles down. (it is not just the tacometer that goes up and down, the engine actually speeds up and slows down a few times). this has nothing to do with the speedometer. If it is a sensor problem then it should show up as a trouble code. These codes do not always turn the light on the dash so you should have the vehicle scanned anyway.
A loose or partially dirty connection?? A 'iffy' rubber vacuum hose??
Something is causing the sensors to get some incorrect information. Definately a sensor problem like the Throttle Position sensor. The revving and settling down is the computer compensating fuel for a bad signal off a sensor.

Go to Advance Auto Parts or an AutoZone. They pull your trouble codes for free and you can isolate the problem. So wherever they bad connection is it will throw a code that will let me know? Thanks. hopefully that will fix the problem and it wont cost much. Im not sure what engine Im tring to help you with but if the fuel pressure regulator is bad it would cause the same thing. Its more likely then a throttle position sensor or idle air control because the truck runs fine the rest of the time. The truck will also start back up quickly if just shut off for a few seconds and harder if left overnight. The fuel is allowed time to drain away from the fuel rail. Does yours do this? Shag, first of all the engine is a 350. Second, it doesn't do anything consistently but what you described is the general trend. I replaced the Idle air control valve about a year and a half ago. I just went to autozone to get my computer scanned and these are the codes i got
1 - IAC Circuit Condition or Idle speed higher/lower than expected (P0507)
1 - Multiple Cylinder Misfire (P0300)
2 - MAP/BARO or MAF/VAF sensor condition (P0108 and P0102)
2 - Catalyst efficiency low - bank 1 and 2 (P0420 and P0430) (I think these are caused by the misfires)
I got in my truck today after not driving it or 2 days and i had to crank it for a while before i received any signs of life. When it finally turned over the rpms were so low that i could hear each cylinder fire and then all of a sudden it smoothed out and the rpms shot up to about 1300 and then slowly fell back down to a nice idle. When i gave it gas after that it would stumble and then accelerate, this slowly worked its way out after about 5 times. So if i had a bad fuel pressure regulator it would cause the fuel to not stay in the lines forcing my fuel pump to fill the lines back up with fuel and then re-pressurize it before the engine can start. Is this correct? That sounds like the problem to me. As a suggestion ,,,you could try cleaning bothe the MAF and the MAP sensors. They do get dirty and this will play havoc with an idle.
Theres plenty of articles online on how to do this. Sounds like what my car was doing when the fuel pump was going out.

Try to get a fuel pressure reading.

Verify you dont have a leaking injector, that can cause same/similar problem. how can i get a fuel pressure reading and how would see if i have a leaking injector? If you have a leaking injector you usually will notice a fuel smell when getting out of the car after driving, if you dont smell it from inside the car get out and open the hood.

You can also put the key in and turn it to "run", not to start but to "run" and the fuel pump will/should pressurize the system, at this point open the hood and examine each injector to see if you can see the leak, which would look like a wet spot and/or smell it.

To get a fuel pressure reading you will need a guage of some type connected to your fuel system. Some vehicles have a schrader valve(this a valve like the one on your tires) and that can be used for testing fuel system pressure. You can also buy a guage and a "T" fitting to attach that guage to your fuel feed line. Be sure you use the feed line and NOT the fuel return line.

When I did this I used parts from Jegs.com, here are the part numbers:

555-41013 - gauge(they have other colors etc)
555-15270 - 3/8" adapter
555-15271 - 1/2" adapter

Can find them all on this page:
http://www.jegs.com/webapp/wcs/stores/s ... 0_-1_10677

I did this because I had a car that had a "lazy start" problem and/or took extra cranking but would run normally through several stops during the day and then all of a sudden not start and require a tow. I found out after installing the fuel guage that the fuel pressure would die off if the car was revved up- reason was because the pump was "slowly dying". After replacing the pump the car has started fine every time, holds fuel pressure with added engine rpms and hasnt left me stranded yet in several months.

Also, if you do end up needing to replace the pump youll have two options. You can buy the whole pump assembly that goes into the tank and it will be exspensive usually over $300, OR you can replace just the actual pump itself for usually under $100-$150. If I remeber correctly the fuel pump for my car was like $85 at Autozone.

Edit: It seems like from what you said that if it is left to sit for a couple days it is harder to get it to start, I wouldnt think a bad/going bad sensor would do this, possibly though. When you let your vehicle sit the fuel pressure in the lines slowly goes away, overnight it will return to 0 psi under normal conditions. My vehicle that had the leaking fuel injector was left to sit for a week and took 4 long cranks to start and once it did it ran horribly at first- sputtering and idle was jumping around.Car Repair Talk's forum.