87 Silverado 350 tbi idling rough

[1fishinrogers]

I need some help straightening out a problem with the idle. It has a very rich gas exhaust and is loping but not all the time. It levels out and idles high occasionally but it doesn't last long. It also has tried to go dead in a pull a couple of times. It belonged to my dad and he never really took care of it from the day he brought it home 24 years ago so I started replacing most of the sensors: both oil pressure sensors, upper temp. sensor, idle air control, throttle position, new wires plugs dist. cap rotor button, ign. coil, vacuum hoses, set timing to factory setting, and rebuilt fuel reg. but haven't yet checked pump pressure. I also sprayed some cleaner in the mass air inlet port which helped at the time but didn't cure the loping but did stop it from going dead when it came down to idle. I unplugged the spark control mod. while it was idling and it didn't change anything, thought that was odd, maybe not?  Any suggestions.

[VileZambonie]

Sounds like the EGR is hanging open. This is usually caused by a sticking EGR solenoid or carbon in the EGR. Pull the vacuum hose off of the EGR valve and plug it. See if that makes any difference.

[1fishinrogers]

still doing the same thing, could it be control mod or a bad connection in the wiring?

[Tazman]

Do you have any stored codes?

[1fishinrogers]

I do now the cil came on yesterday. Going to check it today and get back.

[1fishinrogers]

I went to check for codes but the cel doesn't come on when the switch is turned on but it does work because it was on the two days ago after it started missing. Can someone tell me where to start looking to find the problem with the check eng. light.

[Tazman]

Have your key turned so the check engine light should be on,carefully move the wires behind the box.Mine was the same till I did this,hopefully the light will come on then.

[VileZambonie]

CHART A-1 - NO "SERVICE ENGINE SOON" LIGHT



 Circuit Description :

There should always be a steady "Service Engine Soon" light when the ignition is "ON" and engine stopped. Buttery ignition voltage is supplied to the light bulb. The ECM will control the light and turn it "ON" by providing a ground path through CKT 419.



 Test Description : Numbers below refer to circled numbers on the diagnostic chart.

If the fuse in holder is blown, refer to facing page of Code 54 for complete circuit.
Using a test light connected to 12 volts, probe each of the system ground circuits to be sure a good ground is present. See ECM terminal end view in front of this section for ECM pin locations of ground circuits.
 Diagnostic Aids :

If the engine runs 0K, check:



Faulty light bulb.
CKT 419 open.
Gage fuse blown. This will result in no stop lights, oil or generator lights, seat belt reminder, etc.
If the engine cranks but will not run, check:



Continuous battery-fuse or fusible link open.
ECM ignition fuse open.
Battery CKT 340 to ECM open.
Ignition CKT 439 to ECM open.
Poor connection to ECM.

[1fishinrogers]

Thanks, you were right on. Reached up behind  cel and pushed on the harness and the light was on. Here are the codes, 12,22,32, 33 ,42, 44. A lot going on it looks like, mostly low voltage signals probably loose or bad connections like the cel. Any suggestions ?

[Tazman]

Do you have an idea how long you did not have a check engine light?Some of those codes could be old and are not an issue still.You might need to disconnect your battery for a few minutes to clear the codes and then run the truck again to see what codes come back.

[1fishinrogers]

I did pull the ecm fuse this morning and cleared the codes. You're right some probably are old but I should know sometime tomorrow what codes are current. Thanks

[1fishinrogers]

I finally had time time to check the codes after clearing the old ones out. The only thing that came back so far is 22, throttle pos. sen. low signal at idle. I unplugged the connector and put some nolox on the terminals and also done the same to all the other sensor connectors. So far the idle problem has stopped and no other codes have appeared.

[VileZambonie]

Noalox or penetrox etc is essentially for aluiminum. If you are getting a TPS DTC check the TPS. Do you have a digital volt meter?

[1fishinrogers]

sure do. what do you suggest?

[VileZambonie]

Test the tps by backprobing it with a T-pin. Set your meter to the dc volts scale, key on engine off, backprobe cavity C of the TPS (grey wire) you should have approx 5 volts. Backprobe cavity B dark blue wire and with the throttle closed you should see approx .5V - now slowly open the throttle and the voltage should steadily increase with no glitches all the way to approx 4.5V If there are any glitches replace the TPS.