I'm know for writing long threads but I like to introduce as much detail as possible. I just bought this one about 3 weeks ago. Honestly it was running okay when I bought it. SES light was on at times but didn't really seem to affect much. I wrote in another thread here that I fixed the 4wd by connecting the vacuum hose (that was hanging there disconnected) to the 4wd actuator. Worked like a champ but for a bit, I had some massive white smoke coming from the truck. Mechanic said it was probably a bunch of stuff that had collected in the emissions canister that was burning off. Before we were even done talking, the smoking stopped so that was all good. Still an occasional SES light, still not running too bad. Shortly after I put a bottle of Gumout in there to clean the injectors and tanked up. This seems to be when the problems started. Seems like sometimes it was in a "good mood" and would run great - no SES light.....then like someone flipped a switch...it'd miss and the SES light would come on and then it would start to not run as well. Noticable loss of power and when coming to a stop, it would sputter and die. As far as running the A/C under this condition, forget about it. It was almost kill it right away. So this continues for about a week. Has its good days and its bad days. When it's good....it's running like a new vehicle with no missing or anything and no SES light. Usually wouldn't even last for a full trip from point A to point B, however. Miss...SES light....rough running. When it's running rough for the most part it's at idle or low RPMs...like trying to drive 20 or 30mph. A few days ago I finally ran the tank to just about empty and refilled. Thought maybe the Gumout was causing this stuff. No such luck. Now it is pretty consistantly bad. SES light is always on and it always wants to die when stopping while in gear. When I start it up, it'll sit there and idle okay usually. If I'm just pulling in from somewhere and put it in park....it still may die eventually. Today I had to do to the car dealership to have a GM scanner look at it and the guy said it was throwing a 32 and a 34 code. Low sensor voltage on the MAP sensor and the EGR valve. Well....the EGR valve is bright and silvery so I'm guessing it is probably not very old. MAP sensor may be. However, I remember reading today in this forum that disconnecting the MAP sensor should put the computer in "open loop"....right? And then it should use the throttle sensor to distribute the fuel and ignore the MAP. Even when I disconnect the MAP it does the same thing. Rough running...dying when stopping, etc. I checked voltages with a voltmeter and the +5 volts is there at the sensor. So I'm not sure what's going on. The guy at the dealership said it may be in the wiring. And I guess that could be. But I'm not sure. I'm hoping it's not the ECM. I know my mechanic said to try a new MAP sensor and see what it does so I may do that. I also saw remanufactured ECMs on the internet for about $100. Thinking about that too. After spending probably 10 hours now reading through threads on this forum (and being pretty broke these days) I'm a little gun-shy about spending money to fix something that doesn't need to be fixed. Mechanic said the MAP sensor should be about $50 to $60. Oh...my mechanic also checked fuel pressure today and it's right where it should be. About 58psi at prime and he said when running it's about there and when it's trying to die (doing the vruh....vruh....vruh...vruh...put put put...) it actually ramped to around 60 to 62. So I think my fuel pump is okay.

Suggestions? Ideas?

UPDATE 9-23-09 - Not much to actually update. On the day I posted this, I had a "good mood" incident. Didn't last long but I hadn't seen one in a while. Started up, no SES light, ran great, turned on the AC, still ran great! Got to my shop and shut the vehicle off. Later when I started it again the SES and missing was back.
Other thoughts: Did I read somewhere that the MAP sensor, the EGR valve, and the TPS all share a common ground - that being the gray wire??? Could it be a faulty or flakey ground? I took my voltmeter and grounded it with the gray wire and then put the + on the +5v wire.....showed 5 volts. It wouldn't do this if the ground was bad, right? But it would make sense that it's getting low sensor signals from the EGR and the MAP. Why would these at the drop of a hat decide to behave and all is good. Can the sensors themselves cause this rough running and misfiring? Can something ELSE be causing the rough running and misfiring, and in turn would cause the sensors to give bad readings? On another thought.....I notice sometimes my voltage guage on the instrument cluster show right about 14 or just slightly past. Other times it's showing like 16 volts. Yet at the 16 volt times, I guarantee you I haven't done anything different or done anything to drain the battery to cause the alternator to want to put out extra voltage to try harder to charge the battery? Ground problem somewhere else?? My oil pressure guage will usually average around 50....but sometimes it's showing as high as like 60! What would cause HIGH oil pressure?
There you go....in case you needed more info. Taking a look at the big picture....it seems there is lots of flakiness going on. Which makes me tend to think it's something bigger and not just the MAP sensor. That's why I thought of the computer (ECU?). However is it also possible it's still possibly a bad ground or something ... maybe bad ground wire on the alternator? I cleaned the battery terminals the other day (the day I originally posted this post) very clean. There wasn't any corrosion anyway but nonetheless made sure they were nice and shiny and making good contact.

Please guys...any thoughts would be appreciated. Am I really the only one that's had these types of problems?

 

Well no one is replying, but apparently people ARE reading....so for the benefit of those reading, here's some more info. First off, I added the mileage to my signature. I noticed I hadn't done that so I'm sure there are folks wondering how many miles it has on it. 150,000. Had 149,300 when I bought it almost a month ago. Just rolled 150,000 yesterday. So for whatever that's worth...there's my mileage.
I decided to tinker a little more yesterday. The more I thought about it, the more I thought maybe there's something going on with a ground. Yesterday morning I popped the hood and noted that this bracket on the right side of the alternator (looking at it from the front) was loose. Well the bolt was loose. I originally thought JACKPOT! Not-so-good ground on the alternator! I tightened that down. Didn't make a difference. Still same old same old with SES light and missing. Late yesterday afternoon I removed all the connections on the alternator and cleaned them and tightened them back down tightly....including another mounting bolt that wasn't tightened all the way down. The ground theory sticks out just because of the intermittance of this problem. Plus the fact that sometimes my voltage guage is showing a little above 14, and when it's not running well...it's showing more like 16. The other thing that made sense is a good amount of noise on the radio. I purchased a bracket and a stock Delco stereo a couple of weeks ago. It looks perfect and sounds good, but I also listen to a good deal of AM radio and on the AM side there's noise...even on a local station. That could be unrelated and mean that I just need to attach a ground braid to the back of the radio and attach the other end to the frame. Anyways....a bad ground from around the alternator would cause noise like this. I was really hoping this would solve it, but it did not. I will say that yesterday afternoon I had a trip all the way home (about 3 miles...city streets) with no SES light and it was running perfectly!! It AMAZES me how perfect it can run. After I got home, I ran back to town an hour later and again...still no SES and still running perfect! On this trip I took the freeway as a shortcut. Accelerated up to about 75 (that's the speed limit) and cruised for a bit....then it lunged...a miss.....yep the SES light came back on. Got to the bottom of the off-ramp and it sputtered right out. So back to that. This morning, same story on the way to work here....doesn't want to run and have to either pop into neutral and keep it revved if I'm going to stop....or put one foot on the brake and other on the gas to keep it running although it doesn't like that as much...I feel like i'm straining it.

Could it be still bad ground? Especially with the MAP sensor and EGR sharing common ground and the errors are 32 and 34....MAP and EGR errors for low sensor voltage. AT night I don't get the typical flickering of lights that a bad alternator would signify but still could it be the alternator??
I've been researching and reading more threads this morning and it seems like there are so many engine component problems that don't apply (things like plugs, distrib, cap, wires, fuel filter...) because that would consistant. This is pretty consistant, but it CAN decide it wants to run well and DOES and runs perfect! All in all I'm still pretty stumped. My mechanic said to change the MAP sensor. Should I try that? Would a flakey map sensor also cause it to throw an EGR code too? I guess it is also possible that even though this EGR looks brand new maybe it's bad? Would a bad or flakey EGR cause a MAP sensor code too? Even my mechanic is not sure. He's got a scanner but it's just like Auto Zone's scanner and won't read my codes. That's why I had to go to the GM dealership. Good thing it's a small town and I knew the guy in the service dept that read my codes for me. He didn't charge me and HE seemed to think wiring...he even let me borrow the service manual....I just have to bring it back when I'm done. They are actually a GMC dealer. We do have another dealership in town that's the Chevy dealer...I just didn't want to deal with them and I knew the GMC dealer would have the exact same service manual since they're the same manual.
I have another mechanic that's a customer of mine...might stop and try talking to him today and see if he can give me any info. Why do i feel like no one wants to help me?? The scariest part is that if my mechanic doesn't know.....what happens if I take it in to a mechanic or to a dealership? I'm afraid they're gonna sit there and throw parts at it and change every sensor and so forth.....with a bill coming to a thousand dollars that I DON'T HAVE. Plus who is to say they don't replace something and it runs well when they test it so they think it's done and all along it's actually just having a "good mood" moment and running perfectly.....only to go back to running crappy the next day or the next hour after I pick it up.
I really would like to get this fixed. I'm not a mechanic but I'm a computer tech and also know a lot about electronics and stuff so I do have a volt meter and know how to use it....I can try things and test things and change out parts. I don't mind tinkering. But right now I can't seem to get any ideas. However, winter comes early in Wyoming and I would much rather be working on my vehicle right NOW while the weather is nice...NOT when it's bitter cold and snowing. I don't even have a garage to work in.

 

Well for all who have been reading/following this thread, problem is solved. I wanted to post the results so that maybe it could be helpful to someone. First off, don't over-think it. My problem actually ended up being pretty simple. Knowing the SES codes were 32 and 34 (MAP sensor and EGR) I talked to another mechanic friend. He thought the EGR valve was sticking. He said if the EGR valve is stuck it's certainly like driving with a huge vacuum leak. Made sense. YES...when it's running crappy, it IS like there is a huge vacuum problem. Well with all the posts about EGR valves here in the forum I decided to pull mine and look at it. Figured it got carboned up possibly when I re-hooked that vacuum hose for the 4wd actuator (which had not been hooked up for at least 2 or 3 years under the previous owner) and then for a good 5 to 10 minutes it did some MAJOR smoking. Mostly white smoke but apparently LOTS of crud collected in the cannister due to that vacuum leak that was going on for YEARS. I theorized it was possible that all this crap burning had crudded up the EGR valve and possible the MAP sensor too. When I pulled the EGR it was pretty black, however it seemed to be working. Was NOT stuck or sticking but I cleaned it anyway. MAP sensor....hard to tell but I could see a little dot of gold inside of there. Went to Auto Zone and the guy showed me a new MAP sensor....with a nice little gold circle visible inside there. "Oh, well mine doesn't look like THAT!" I said. Bought the map sensor and decided to wait on replacing the EGR. The guy said if it's operating and not sticking and sealing right, then it's probably okay. So I stuck it back on. Put the new MAP sensor on. Problem SOLVED!!! Been running like a champ ever since. That was over a week ago now. I DID still get an occasional SES light but this time it didn't affect the running of the vehicle at all and then it would go away and not come back for a day. Couldn't get it to do it for long enough to even get it to the dealership and have my friend hook up the GM scanner to find out what code. The gasoline was just plain old regular unleaded (87 octane). It came time to get gas and I decided to go with mid-grade (89 octane) this time just to maybe give me a little boost in power/gas mileage. Ever since I tanked up with the mid-grade, the SES light has not come on at all. Not even once. And again, that has been about a week now....no ses light at all. I am not sure what all this means but it's running just great with no SES light at all. I can run the A/C all I want and it's perfect. Well it RUNS perfect.....air flow for the AC is messed up right now and it comes out of whatever vents it wants to, depending on engine speed. I am pretty sure the rotary vacuum valve on the back of the HVAC control is leaky.....it hisses constantly when it's in any position but OFF. That's another problem I'm going to have to try fixing soon since winter is here....we've had cold temps with frost on the windshield and had a day of snow.....and snow on the way again tonight. I need to have the defroster working properly....not blowing wherever and whenever. I think a trip to the junk yard (nearest ones are 80 miles away in Salt Lake City, UT) is warranted. But hey that's another thread

So anyway, problem solved. Hope this info is useful to someone.

 

thanks for posting an update to what fixed it, because mine just started doing what yours did. I'll head to the parts store today. thanks