Ugh Stalling

1990 Jimmy 4.3 liter 262 tbi. 141000 miles.

So I've read basically every post in this forum regarding EGR stalling. I've cleaned, then flat-out replaced my EGR valve and have had no luck. The stalling occors after the engine has warmed up, and is sparratic in nature. The sputtering often times occors at highway speed as well, making the engine jerk. Coincidentially, the oil pressure seems to drop in synchrony with the stalling at idle, and gets dangerously low (often as low as 10-20psi). I have taken all the necessary steps (outside of replacing the injectors) to cure this issue.

Plugs (Delco)
Wires (Delco)
Cap/Rotor
Fuel Filter/Pump
Fuel Cap
Radiator Cap/hoses/180 degree thermostat
Coolant flush
Temp sensor
Timing is accurate as well

I've dumped an assload of money and time into this issue to no avail. The engine has also recently developed a knock (as if it's overheating). My patience (as well as my budget) are growing thin and I hope that someone can give me a clue as to what I'm missing, because I'm on the virge of dropping an ad in the paper for it.

Ok, I've also noticed that it seems to be running rich. I'm noticing a carbon "splatter" on the concrete coming from the tailpipe, when I first start the truck. Could the stalling and splatter pattern, as well as the other symptoms be a possible indication of catalytic converter failure?

PCV replacement?
air filter?
have you cleaned the throttle body?
have you ever taken off the egr and blown the chunks out of the intake?
have you ever ran any injector cleaner?

any codes?




Ok, I've also noticed that it seems to be running rich. I'm noticing a carbon "splatter" on the concrete coming from the tailpipe, when I first start the truck. Could the stalling and splatter pattern, as well as the other symptoms be a possible indication of catalytic converter failure?

PCV replacement?
air filter?
have you cleaned the throttle body?
have you ever taken off the egr and blown the chunks out of the intake?
have you ever ran any injector cleaner?

any codes?

yes
yes
yes

No codes.

ever replaced or checked oxygen sensors? ... a bad or dying O2 sensor might getting a false reading from the exhaust and then telling the engine to run leaner or richer?

vacuum lines? ... I recently found some on my 97 Jimmy that were completely dry rotted out ...

you might also try the "screen" type of EGR gasket ... some on this forum recommend it, some don't. It seems to me that the screen keeps chunks of carbon from getting into the EGR but not always from blocking the passage ...

do you have an air pressure sensor on this vehicle? (MAP ?) if so, have you cleaned it? ...

ignition switch? ... kind of a stretch ...


yes
yes
yes

No codes.

ever replaced or checked oxygen sensors?

I have not checked or replace. How exactly do you go about checking an O2 sensor?

vacuum lines? ... I recently found some on my 97 Jimmy that were completely dry rotted out

Checked, checked, rechecked. I had one that came up from the wheel well very near the battery that was clogged. Fixed. Still idleing rough.

you might also try the "screen" type of EGR gasket ... some on this forum recommend it, some don't. It seems to me that the screen keeps chunks of carbon from getting into the EGR but not always from blocking the passage

EGR was fine. No immediate concern, just a little surface carbonizing, and no clogs in the intake.

do you have an air pressure sensor on this vehicle? (MAP ?) if so, have you cleaned it?

I don't know if this model does have a air pressure sensor or not, and if it does, I have no idea where it's at. I've also been trying to locate an Idle Air Control Valve with no luck. Any ideas or knowledge would be appreciated.

This problem, literally, just happened. One second it was fine, the next it was idling horribly, stalling, ect. It's not like it was a gradual issue, and it only occors after the vehicle has been running for more than 10-15 minutes. PLEASE HELP!!!!!!

I'm not sure how to check an O2 sensor. I do know that they need to "heat up to temp" before they start doing their job (assessing the exhaust contents and then sending a message to the computer to adjust richness/leanness). This might explain your worse idling after 10 minutes or so ... it has taken time for them to warm up ...

I think its safe to say that replacing the sensors after 100,000 miles is not unreasonable. I'd start with the one after the cat converter. On my truck you need a special tool (you could probably rent one). It is essentially a socket with a long slit in it. This will make sense when you get under the truck and look at it. New sensors are approx 60 - 80 bucks a pop.


Also, have you cleaned the Intake Air Temp sensor? It should be in your air intake duct between the air filter and the air intake ... probably in the duct itself. It could be that this is the same thing as the Idle Air Control Valve (any experts out there??) that you mentioned. Anyhow,clean the sensor and check the wire harness connections and wires. This sensor of course responds to temp which might explain your worsening idle on the highway problems (cooler incoming air). Maybe a "long shot" but it's worth a quick check ...


Also, its possible that your Throttle Position Sensor is dying or shot. A broken or loose TPS can cause intermittent bursts of fuel from the injector and an unstable idle because the computer thinks the throttle is moving. I'd try another clean with the Throttle Body cleaner first ...


Also, if you have one, Air Pressure sensors are usually located near the throttle body on the intake manifold.


Plugs gapped correctly?



I have not checked or replace. How exactly do you go about checking an O2 sensor?



Checked, checked, rechecked. I had one that came up from the wheel well very near the battery that was clogged. Fixed. Still idleing rough.



EGR was fine. No immediate concern, just a little surface carbonizing, and no clogs in the intake.



I don't know if this model does have a air pressure sensor or not, and if it does, I have no idea where it's at. I've also been trying to locate an Idle Air Control Valve with no luck. Any ideas or knowledge would be appreciated.

This problem, literally, just happened. One second it was fine, the next it was idling horribly, stalling, ect. It's not like it was a gradual issue, and it only occors after the vehicle has been running for more than 10-15 minutes. PLEASE HELP!!!!!!

do you smell a strong odor of gasoline ??



I'm not sure how to check an O2 sensor. I do know that they need to "heat up to temp" before they start doing their job (assessing the exhaust contents and then sending a message to the computer to adjust richness/leanness). This might explain your worse idling after 10 minutes or so ... it has taken time for them to warm up ...

I think its safe to say that replacing the sensors after 100,000 miles is not unreasonable. I'd start with the one after the cat converter. On my truck you need a special tool (you could probably rent one). It is essentially a socket with a long slit in it. This will make sense when you get under the truck and look at it. New sensors are approx 60 - 80 bucks a pop.


Also, have you cleaned the Intake Air Temp sensor? It should be in your air intake duct between the air filter and the air intake ... probably in the duct itself. It could be that this is the same thing as the Idle Air Control Valve (any experts out there??) that you mentioned. Anyhow,clean the sensor and check the wire harness connections and wires. This sensor of course responds to temp which might explain your worsening idle on the highway problems (cooler incoming air). Maybe a "long shot" but it's worth a quick check ...


Also, its possible that your Throttle Position Sensor is dying or shot. A broken or loose TPS can cause intermittent bursts of fuel from the injector and an unstable idle because the computer thinks the throttle is moving. I'd try another clean with the Throttle Body cleaner first ...


Also, if you have one, Air Pressure sensors are usually located near the throttle body on the intake manifold.


Plugs gapped correctly?

Ok, so I've put the thing on the diagnostics. No codes. Shows that the 02 sensors are opening and closing, running between lean and rich. The temperature sensor is working, coming back 190 degrees after running for 20 minutes. IAC sensor is functional, as is MAP. Timing is good. I've also checked for leaks in my intake manifold gasket. None. I've re-gapped my plugs, I've checked the timing, and fuel pressure, and IT'S STILL IDLING ROUGH! Please HELP!!!

FIXED! At least temporarily. And wouldn't you know it, the ONE plug that I didn't re-gap (due to the pain in the ass it is to pull that particular plug) was the culprit. For some reason an excess of brown ash had built up on the plug causing it to not fire. A good deal of ash build up. Just a little fyi for anyone ever experiencing this problem: When a brownish ash is apparent on a plug, it is indicitive of a couple of problems; If the ash is on one side of the electrode, this usually indicates a problem with the cylinder head (valve seals or valve guides). If the ash is apparent surrounding the entire electrode of the plug it is generally indicitive of piston ring failure.

So I've replaced the plug and the engine idles fine now, however it looks like I am going to need to do a valve job soon. Oh boy.