95 GMC misses/runs rough after warmup

Hey people
I have a 95 GMC c1500 pickup w/5.7 & auto. The problum is as follows. When staring with a cold engine it runs fine but, as soon as the engine warms up to operating temp (only a couple of minits) it will hesitate/stumble around 1200 to 1800 RPM yet it will idle just fine. It does not matter weather it is under a load or not. Check engine light is not on & has no codes present. It was doing this when I bought it with 161000 miles. have replaced the following mostly because it really needed it; cap, rotor, coil, plugs, plug wires, map sensor, tps, fuel filter. Also have checked the engine gound wires & checked for vacuum leaks. Since it runs smooth at idle I don't beleive it has vacuum leaks. The spary pattern for the injectors seems to be fine. I have not checked fuel pressure but since it accelerates fine under full thottle I did'nt think theres a problum with the pump. Is anyone here familar with these symptoms? Are there common issuses with the base plates wearing out on the throttle body? Or do the distributor bushings wear out? Im stumped!!!

check the EGR valve, sounds stuck open to me but I could be wrong.

I have a 99 with the same set up. I do have a Service Engine Soon light on. Mine is making the same problem. Autozone checked it and said I need a new catalytic converter.

thanks for your responce guys, to Carpenterbill---- I have been courious about the EGR system, I can move the EGR diapharm with my finger but I know it is not a good test. to 99silverado----- since my truck accelerates fine under full power logic tells me the cat converter is not blocked , and as for the guys at AutoZone----- are you really going to trust what they say????? All they are good for is giving codes.

anyone else ??????

try again

my truck is doing the exact same thing. 95 gmc yukon. any suggestions?

95gmcyukon, welcome to the forum!!!
 
Have the injectors been checked or serviced lately?

Your coil is bad.  Replace the ignition coil, it's cheap too, probally $30.
 

no the coils is not bad. I have replaced it already!

Has it had a injecter service recently?

This one is going to be fun!!! Check your MAF, see if your EGR tunnel is clogged, other than that I have absolutely no damn idea.

Going back to the autozone comment- If all they are good for is giving codes, and the code the the SES light gave was catalytic converter, then how are they wrong?  Are you getting an engine light too or does it just run bad?..

Thanks for the responces guys! 
Northy87----- Define " injector service".   Mine has the T-body injectors, the spray patterns look good but I know thats not a good test. How do you service the injectors?
 
Transam man--- mine does not have a MAF (mas air flow right?) since it is t-body injected.  Good idea on the EGR tunnel!    How about the EGR solinoid????? Do they cause problums?
 
Jmack----- I never had AutoZone give me codes, that CAt converter thing was someone eles. Also I did not mean they're code readings are wrong.  I had checked for codes myself with a scantool & none were present at that time & no --- no check lite is on.

Sorry, I'm too used to my trans am. There are a couple ways to clean your fuel injectors, my favorate is using kerosine. You can also go to the store and get injector cleaner but thats no fun. You can poor whatever you want to use right into your fuel tank, usually 20 ounces will do it. If you want to go all out on it go here:
http://www.ehow.com/how_2044858_clean-fuel-injectors.html
http://www.aa1car.com/library/2003/ic30336.htm

Well ----- now that you bring it up, I have ran a couple of cans of "Sea Foam" through the tank with no efect.

Well the dealership will hook up a pressuerized can of BG44X and run the truck to clean the injectors, but you can get it in a pour-in-tank form from http://www.autobahnpower.com/products.asp?recid=542 Great stuff, powerful, and cat safe. One can will do about 15 gallons.

im in the same boat, i need help.  my truck runs like crap...especially 1200-2000 RPM
 
Harmon

hey guys,
names eric and im a zone guy sorry! but it souns like your o2 is bad, now before you say my check eng light isnt on , you knock senscore is why its not coming on you have obd1 not obd2 but anyways when youre o2 heats up it changes the fuel/ air ray.
ok try chaning it, if that doesnt work the check the wire, i know you said you alredy changed the but try testing the oms, after that go to your egr stuff and yes that selanoid well cuse you probles but unlike those ford guy our o2s go out first.

95k1500z71
    Thanks for your input. Are you saying that the OBDI will not set a code for the o2 sensor? Or is there an issue with the knock sensor?

That sounds like a pretty good guess, usually when the 02 is going bad your fuel economy goes bad too, have you noticed that?

on obd1 youre knock wont pick up small things ie miss fire,bad o2. thats why all new cars have a millon senscore where the older cars dont. you may not see a drop in fuel ecom, the o2 has a hot/warm and a cold setting, so it sounds like thats where youre having issues. when i got to work ill get you the read out for a bad o2 and you can see if it mattchs.

Yea, my fuel consumption is about 17 / 17.5 on highway, thats about as good as they will do I believe.

use an obd2, and x2 on the o2 sensor, or the temp sensor

WHAT??????         what are you talking about Iceman?