92 Chevy C1500 W/Rough Idle

[Rudyfastcat]

I have a 1992 Chevy C1500 w/ 4.3L(V6) and manual trans.
My truck just developed a rough idle this week .

My problems originaly started when my EGR went bad and I replaced it about 2 weeks ago.
I replaced it and the solenoid with an after market one (Auto Zone) and found that the problem got worse I eventually bought a AC Deloco OE EGR & solenoid and all seemed well until this week when I started feeling the idle a little rough,
Now I have gone ahead a replaced the Dist.(cap & rotor too), plugs, wires, coil and IAC and still nothing has changed. I have even chaged the sparkplugs and wires twice just in case and still nothing has chnged.
I still have good power and I do not notice any problems while driving just while sitting at idle or in nutral (no boging)
Is there somthing that I am missing ???? Please help

[superchuckles]

how long since you replaced the o2 sensor? they recommend 30k to 50k miles replacement - if it's not functioning, it can be trying to over-richen or lean & would cause this type of condition

[Rudyfastcat]

Originally Posted by superchuckles

how long since you replaced the o2 sensor? they recommend 30k to 50k miles replacement - if it's not functioning, it can be trying to over-richen or lean & would cause this type of condition

The O2 sensor was one of the first things I replaced after this prob. started ... I'm thinking that maybe I have a vacuum leak or maybe carbon build up in the intake....

[superchuckles]

check your throttle position sensor (TPS) - once you determine which of the 3 wires (5v+, gnd, & data) is your data wire (by process of elimination using a voltmeter) turn the key on, but don't start the engine - slowly move the throttle all the way to the full open position, all the while watching the voltmeter. it works best with an older analog meter, but digital will work ok. if there are any points where the voltage suddenly spikes one way or the other (remember, we're only talking a max of 5+ volts measuring from gnd to the data wire) it needs to be replaced. if you aren't showing a nice smooth transition from around half a volt in the idle position, & near 5 volts in wide open throttle, it needs to be replaced. a tps can go bad & not throw a engine check code (had it happen more than once) and it will make it hard to keep running at idle. if that checks out ok, i would pull the air cleaner off & fire it up & watch your injectors - are they flushing too much fuel? if you disconnect the vacuum to the egr, does it run any different? if so, then the solenoid on it is stuck open - egr should never open at idle.

[Rudyfastcat]

Originally Posted by superchuckles

check your throttle position sensor (TPS) - once you determine which of the 3 wires (5v+, gnd, & data) is your data wire (by process of elimination using a voltmeter) turn the key on, but don't start the engine - slowly move the throttle all the way to the full open position, all the while watching the voltmeter. it works best with an older analog meter, but digital will work ok. if there are any points where the voltage suddenly spikes one way or the other (remember, we're only talking a max of 5+ volts measuring from gnd to the data wire) it needs to be replaced. if you aren't showing a nice smooth transition from around half a volt in the idle position, & near 5 volts in wide open throttle, it needs to be replaced. a tps can go bad & not throw a engine check code (had it happen more than once) and it will make it hard to keep running at idle. if that checks out ok, i would pull the air cleaner off & fire it up & watch your injectors - are they flushing too much fuel? if you disconnect the vacuum to the egr, does it run any different? if so, then the solenoid on it is stuck open - egr should never open at idle.

Okay I tested the TPS and found voltage spikes out of specs . I replaced it but still no change .
Some thing else I noticed is that it idles real smooth when cold starting but once it reaches operating temp. the rough idle returns.
Any other things I need to look at ??

[superchuckles]

clear & recheck any engine codes (if any) first. second, i'd re-check your egr valve - make sure it's ok - also, you didn't by any chance use any silicone on any gaskets did you when replacing said egr valve? (RTV). some types can kill the o2 sensor if i remember right. if you're getting good idle cold, but not warm, you may have a faulty fuel pressure regulator (check return pressure), or perhaps an injector leaking at idle, or any sensor that works primarily in closed loop, like the o2 sensor. there is one thing about the TPS that when it's installed, some need adjusting (depending on type - the kind with metal tabs can be adjusted by slightly bending said tab). you should be getting an 'in-circuit' voltage on the data wire that's very close to zero at idle, but i can't remember exactly what that voltage is right this second & it's late - i'll try to remember to check tomorrow. that was what turned out to be my trucks rich idle problem. it was seeing the throttle being open further than it actually was. if you have something like an autotap cable for your truck & can hook it to a laptop, it will show you all the live readings - helps immeasurably - i made of for a 92 gmc myself & it cost me all of about $12 to build.