95 chevy running rough, can't find problem!

My 95 1/2 ton silverado with 5.7L is running rough, and I can't find the problem. It acts as if it is going to stall when I accelerate and begin to slow
down. Once I stop, it idles good. The check engine light doesn't come on. I replaced the fuel filter, air filter, distributor cap & rotor, and ran 2 bottles of fuel injector cleaner thru the system. I also cleaned the idle control valve. None of these things helped. When the truck sits for several hours, like overnight, it doesn't begin acting up immediately, only after a few minutes of driving. Any ideas on what could be wrong??
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My guess is that it is running lean after warm up. I would put a vacuum guage on it and check for leaks, broken lines etc.

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I may very well be out in space. But my friend's Buick Station wagon, the throttle position sensor was bad. It was a PIA to replace, but it made a big difference.
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Jeff wrote:

clicking noise from under the dash when the truck stumbles or runs rough. In my case I can corroded battery cables. I had to peel back the insulation on the cables to find the corrosion. And the corrosion was quite a ways up the cable from the battery connections. Hope this helps.
Bob
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Jeff wrote:

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How do I test the EGR valve? Are they expensive to replace?
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Jeff wrote:

Most often the valve seat (in the intake manifold), the actuator shaft, and the pintle become coated with carbon. Usually, this causes an extremely rough idle. There are a couple of bolts mounting the EGR to the manifold--not fun to get to, but with patience, it's not bad. If it's gunked up pretty bad, you can use some carb cleaner to clean it up. It's a pricey item. I think somewhere around $135 or so.
Also, sometimes the EGR mounting bolts will work loose and cause an air leak.
Good luck.
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Basically these newer vehicles have a lot of different electrical components which give input to the engine computer and then a lot of components in the fuel injection system.
The *new* way to find these problem is to "test" various components to see if they are operating as they should. Then you would know what is working ok and does not need to be replaced. Which needless to say can save a ton of money as opposed to the "guess and replace parts" strategy.
For testing all this stuff, you need a GM Factory Service Manual set for your year/model vehicle, a multimeter, a fuel pressure gauge (they make one for GM TBI vehicles), and in some cases an exhaust pressure gauge which would go into the oxygen sensor hole for testing exhaust back pressure.
Then just find the symptom in the shop manual, then it would have detailed troubleshooting instructions for the symptom. Sometimes several pages of things listed to check.
You can order a Factory Service Manual set from helminc.com or from a GM dealer. They cost about $135, but you get what you pay for. Anyway get the right tools for the job.
As an example of a test, there is a "coolant temperature sensor" which tells the engine computer what temperature the engine is running at. Very easy to test. Place a thermometer in that area, unplug the electrical connector, place your multimeter on ohms, then read the ohms on the two connectors for the sensor. Then look up in the shop manual what the resistance (ohms) should be for that temperature.
If it is reading what it should, then no need to replace. Say that sensor costs around $25, well you just saved yourself $25! Then on to the next sensor.
With the shop manuals it is sort of the case of "too much information". Something like the above coolant temperature sensor may be listed in 4 or 6 different spots in the various manuals (4 different books to set). So may take a bit of learning of where to find the information you are looking for. But that is a lot better than not enough information provided...
As to shop manuals, older sets have a general service manual, a fuel and emissions service manual (engine troubleshooting), an electrical diagrams manual, and a unit repair manual. Newer sets have this all mixed into a 4 book set with each book about 2 inches thick.
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