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Old January 4th, 2011, 09:59 PM   #21
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so even tho the EGR valve is opening too early, but still working is why it doesnt show up when i had a computer hooked up?
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Old January 5th, 2011, 01:14 PM   #22
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so even tho the EGR valve is opening too early, but still working is why it doesnt show up when i had a computer hooked up?
Correct it won't always through a code when it is still working.
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Old January 5th, 2011, 01:26 PM   #23
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alright gotchya! thanks for the info! i got a little time today before work later so i think im gonna go try that out and see if thats the problem. it has been running ALOT better now that its colder out, its more when its in reverse, which im hardly giving it any throttle that it runs rough, but going forward it dont seem to surge as bad as when it was warmer out. but ill try checking the EGR valve and if i find anything out ill post on here to let you all know that have been helping with all the info and ideas
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Old January 5th, 2011, 03:20 PM   #24
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unhooked the vacume hose to the EGR valve and plugged it off and it fixed the problem! Runs good now at low idle/slow speed. Thanks guys... gonna take it off and check for carbon build up Thursday if the weather is good and if im not too busy, might just need cleaned or replace both the EGR valve and intake to save time cleaning out all the ports and passage ways.
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Old January 5th, 2011, 03:29 PM   #25
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dont try to clean it, just replace it, the rubber diaphram inside the valve is weak so egr comes on too soon (less vacuum to open it)

had several of these persomally and at work
im a master certified tech so if you have further questions pm me
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Old January 5th, 2011, 03:50 PM   #26
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so clean the intake if its carbond up, but replace the EGR
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Old January 6th, 2011, 10:31 AM   #27
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so clean the intake if its carbond up, but replace the EGR
Yes replace the egr and if the carbon is built real bad then you could clean it a bit, but I would be more concerned about getting a new egr valve installed.
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Old July 5th, 2013, 04:12 PM   #28
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Default Same problem, but hard to fix.

I just found this entry and thought I would wake people up about this issue.
I have a 1993 GMC Suburban K1500 5.7L TBI which has these same set of problems.
I have changed the EGR valve, and problem remains. I swapped the EGR Vacuum Solenoid and the problem remained. If I disconnect the power connector to the EGR Vacuum Solenoid problem solved as it when I plug the vacuum hose from the solenoid to the EGR valve. I hope this isn't the ECM as that sounds expensive. I have noticed that I have a need to a new connector on the Idel air control valve, but I doubt that is the problem.

So to echo the probelm.
When the engine is cold, the problem is not there, but I also notice the idle is about 800RPM on the tach.
When the engine is hot my problem starts.
1: Runs fine at high speeds, but I can feel the engine surge a bit at 25 MPH, and at 5 MPH it is very noticable ! If I get out and disconnect the EGR Vacuum Solenoid power connector, problem gone. I need to get this fixed as the SMOG is due, which is bad timing! Anyone out there have any more ideas? I have read about the MAP sensor, but would that be a possible cause?
Any help would I would be very grateful.

Last edited by K8WN; July 5th, 2013 at 08:32 PM. Reason: Update new info.
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Old July 5th, 2013, 08:33 PM   #29
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I just found this entry and thought I would wake people up about this issue.
I have a 1993 GMC Suburban K1500 5.7L TBI which has these same set of problems.
I have changed the EGR valve, and problem remains. I swapped the EGR Vacuum Solenoid and the problem remained. If I disconnect the power connector to the EGR Vacuum Solenoid problem solved as it when I plug the vacuum hose from the solenoid to the EGR valve. I hope this isn't the ECM as that sounds expensive. I have noticed that I have a need to a new connector on the Idel air control valve, but I doubt that is the problem.

So to echo the probelm.
When the engine is cold, the problem is not there, but I also notice the idle is about 800RPM on the tach.
When the engine is hot my problem starts.
1: Runs fine at high speeds, but I can feel the engine surge a bit at 25 MPH, and at 5 MPH it is very noticable ! If I get out and disconnect the EGR Vacuum Solenoid power connector, problem gone. I need to get this fixed as the SMOG is due, which is bad timing! Anyone out there have any more ideas? I have read about the MAP sensor, but would that be a possible cause?
Any help would I would be very grateful.
Today I had a chance to try the MAP unit, no change. Same problem. Looking more and more like an O2 sensor or the ECM. Grumble!
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Old July 5th, 2013, 10:23 PM   #30
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Have you checked your vacuum lines for cracks. Those pos vacuum lines like to crack right under the rubber. Twist them off carefully, shoot the internals with a air hose to clean out any oil, then blow in one end while plugging the other.

You can make your own clear plastic ones out of fish tank hose which will allow you to see how blocked they become. You just melt it to create the bends without affecting the factory flow because the fish tank hose has a larger ID. If you use a small piece of metal at the end of the plastic line going into the old "flexible 90" it lets you keep the factory shape. Red jr. dragster hose looks more professional with the same technique. But I am cheap, for $20/4 hours you can do the entire truck and easily see how blocked or if one of your lines is leaking because it will have a oil or condensation streak at the leak point.

A faster and cheaper fix is just to reset your PCM. With every sensor plugged in, clear all your codes, pull your battery out, then turn the light switch on to drain any residual, and wait overnight. Install the battery, then turn the key to the on position and wait for everything to load. Turn the truck on writing down any codes you get, and then take it for a 10 minute test drive driving the truck hard. Do this in a area where if you break down you are not very far from the house or somewhere you can get a tow back.

Write down any engine codes you have. If you have a electronic transmission check it for codes at this point also.

My guess you either have a open EGR sensor, a bad connection at the egr sensor(if it happens at random), a bad connection in the harness, a injector going bad, or a PCM that is going bad or not properly grounded. Pull your IAC and TPS shoot them with some carb cleaner then reinstall and see if anything changes I doubt this is a issue but if you notice a change these parts are cheap. You can get the gaskets for like $2 or make your own if you pull them off and shoot them every 15-20k like I did on an 88 that I had over 340k on when the transmission went out. The last 220k were mine with lots of out of state travels towing a car dolly.
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Old July 8th, 2013, 03:09 PM   #31
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Thanks for jumping in on this. I have a few comments.

The vacuum lines are fine, as I have already replaced them for the same reasons you mentioned.

The engine runs great if I disconnect the EGR Solenoid connection.
The EGR valve, EGR Solenoid, and MAP sensor I have replaced one at a time, and problem still is around.

What I am trying to locate now if a docuemnt that explains "When the EGR value should be open" by the ECM. I mean it sounds like this is only to be opened at higher speeds, and not when I am sitting around at near crawling speeds.

Have had several people tell me to replace the Thermal switch. Its only a $15 part so I think I will try that tonight.

Really been an interesting debug, I have an OBD2 code reader, not sure if that will work on the 1993 OBD1 system. Need to find that one out as well.

BTW: The Check Engine light only comes on while I have the EGR Solenoid disconnected and drive for a period of time on the freeway speeds.
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