Failing Emissions...Low Idle Cyclical Stalling/Surging

I would appreciate any feedback on my problem...
I have had emissions problems for a few years now as can be seen in the following emissions transcript...

Emissions Inspection 6/4/2002
Hydrocarbons (HC) – Inspection 5.3095 – Requirement 2.7000 FAIL
Carbon Monoxide (CO) – Inspection 35.3126 – Requirement 60.0000 PASS
Oxides of Nitrogen (Nox) – Inspection 0.4853 – Requirement 5.7000 PASS
Carbon Dioxide (CO2) – Inspection 476.3944

Work Performed 8/2002
· Adjusted Timing to 0 TDC
· Replace Oxygen Sensor @ Catalytic Converter
· Replace Spark Plugs
· Replace Ignition Wires
· Replace Distributor Cap & Rotor
· Replace PCV Valve
· Replace Air Filter

Emissions Inspection 8/2002
Hydrocarbons (HC) – Inspection 0.1880 – Requirement 2.2000 PASS
Carbon Monoxide (CO) – Inspection 1.9014 – Requirement 60.0000 PASS
Oxides of Nitrogen (Nox) – Inspection 0.0070 – Requirement 4.2000 PASS
Carbon Dioxide (CO2) – Inspection 73.1697

Emissions Inspection 7/13/2004
Hydrocarbons (HC) – Inspection 6.7361 – Requirement 2.0000 FAIL
Carbon Monoxide (CO) – Inspection 62.4512 – Requirement 60.0000 FAIL
Oxides of Nitrogen (Nox) – Inspection 0.3481 – Requirement 4.0000 PASS
Carbon Dioxide (CO2) – Inspection 599.9200

Work Performed 11/2004
· Adjusted Timing to 0 TDC
· Replace Spark Plugs
· Replace Ignition Wires
· Check and Clean Distributor Cap & Rotor
· Replace Air Filter

Emissions Inspection 7/13/2004
Hydrocarbons (HC) – Inspection 4.6401 – Requirement 2.0000 FAIL
Carbon Monoxide (CO) – Inspection 18.6279 – Requirement 60.0000 PASS
Oxides of Nitrogen (Nox) – Inspection 0.2441 – Requirement 4.0000 PASS
Carbon Dioxide (CO2) – Inspection 609.0446

Still notice low throttle, low RPM miss (seems to get a little worse as engine temperature increases). No miss upon acceleration or at high RPMs that I can notice. After engine warm-up and when truck is parked, holding the accelerator slightly so that engine revs around 500 – 700 RPM (approx), the engine will stall, revs will decrease, engine will recover and surge back to 500 –700 RPM, stall, and repeat in a cyclical manner.

Work Performed 11/2004
· Check and clean EGR valve. Valve seemed to be fine, but cleaned.

I'm hoping that someone can give me an idea as to what could be the cause of my problems...I'll gladly reply if further info for diagnosis is required...Thanks

BTW, I forgot to report that the vehicle is a 1994 GMC Sierra 1500 truck with approximately 170K miles on it.

Given your mileage, cleaning the EGR valve won't really help if it is worn out. They take a lot of abuse in the form of heat. If that is the original EGR valve, you really should replace it.

Your rough idle is pretty common for the TBI trucks. It could be the coil pickup, worn dist bushing, vacuum leak, MAP sensor or IAC.

Make sure that you don't have a vaccum leak. I use TB cleaner and spray around the base of the TBI will idling. If the idle changes the TBI gasket is probably bad (very common). Also spray the intake gasket area looking for a change in idle.

Remove the dist cap and look at the pick up coil. If it looks yellow and flaking, it probably should be replaced. Also see if the dist shaft can move side to side. If so, the dist shaft bushing is worn out.

//2000CAYukon

Given your mileage, cleaning the EGR valve won't really help if it is worn out. They take a lot of abuse in the form of heat. If that is the original EGR valve, you really should replace it.

Your rough idle is pretty common for the TBI trucks. It could be the coil pickup, worn dist bushing, vacuum leak, MAP sensor or IAC.

Make sure that you don't have a vaccum leak. I use TB cleaner and spray around the base of the TBI will idling. If the idle changes the TBI gasket is probably bad (very common). Also spray the intake gasket area looking for a change in idle.

Remove the dist cap and look at the pick up coil. If it looks yellow and flaking, it probably should be replaced. Also see if the dist shaft can move side to side. If so, the dist shaft bushing is worn out.

//2000CAYukon

2000CAYukon,

Thanks for the info...I'll try all of your suggestions...

Yes, it is the original EGR valve...I was hoping not to have to spend the $80 to replace it...but am reconsidering it.

Thanks again...and if you think of any other ideas, please pass them on...I'm two weeks from my next re-scheduled emissions inspection.

I have a 97 GMC sonoma with the 4.3 X CSPI with the same problrems. I didnt see anything about you trying injector cleaner. The poppet valve in the fuel injectors are faulty, but unless you live in california, GM will NOT replace them. Chevron with techron, or or prestone has a zero to sixty that is good. It is also possible that there may be something wrong with the spyder unit, or the lines being cracked. Check your ignition coil also, as those seem to fail quite often on these trucks. GO GM!!

I have a 97 GMC sonoma with the 4.3 X CSPI with the same problrems. I didnt see anything about you trying injector cleaner. The poppet valve in the fuel injectors are faulty, but unless you live in california, GM will NOT replace them. Chevron with techron, or or prestone has a zero to sixty that is good. It is also possible that there may be something wrong with the spyder unit, or the lines being cracked. Check your ignition coil also, as those seem to fail quite often on these trucks. GO GM!!

dtl379...Thanks...I'll give your suggestions a try.