Ok my car has been running worse and worse. Today is the worse its ever been. It is running real rough and wants to die when you give it gas to accellerate. If you rev it up in park, it will stumble at first, then start to increase the rpm's. Also, if you manage to get the car started on the road without it stalling when the clutch comes out, if you floor it the car bucks horribly and keeps locking up the rear wheels intermittenly. Also, if you keep it floored at a higher rpm like 3500 rpm it just starts making "popping" noises under the hood untill the popping noises get so bad it sounds like a machine gun and wont accellerate. Also, the idle is erratic and rough and goes between 400-600 RMP and the whole car shakes horribly. And the exhaust smells gassey.

I took the aircleaner off today, and I was revving it up in the parking lot, and every time it "pops" a gyeser of white cloud comes back out the throttle body really loud. Also, after it had idled for a while I tried to rev it up, and it stalled. After the motor stopped, a really big cloud came back out the throttle body for like 2 seconds straight!

Also, I tried disconnecting the weather-pack connector like you do to shoot the timing. It just made the motor barely run at all - i mean it didnt even want to idle without some help. So maybe it's ignition related?

Now here is the cincher: thursday it wasnt raining, but was foggy. I drove to walmart and the car ran bad the whole time. The car sat for 1/2 hour, and I cam back out and drove back to school and it ran even worse. At school, I let it sit for an hour, went back out and it ran perfect.

Yesterday I drove it in the rain twice and it ran great. Today I drove it in the dry weather and it was the worse its ever been, I mean barely drivable. Finally, this problem has never triggered a SES light, however something simple like disconnecting the IAC sensor will throw a code.

[edit] oh, also. In the morning when it is cold it runs fine all the time. It pulls like a **** at WOT. However, the warmer the engine gets the worse the condition gets. Unless its a good day, then it will run fine the whole trip.

 

Alright here is a update. I was playing around while it is still running rough, and I wanted to unplug the vacuum hose for the FPR, figuring if it was running lean this would make it run full rich.

There is a vacuum hose on the back of the throttle body that goes through a narrow plastic line up to this little electronic device bolted to the sheetmetal seam that the rear hood seal rests on. It is black, has the GM logo on it, and has a green plug plugged into it.

When I pulled the vacuum line off the TB, the car wanted to stall so I gave it some throttle to keep it running. Also the injectors were pouring gas out. Then, after like 10 seconds, the car smoothed out. I revved it up, and there was no backfires or anything! What does this thing do?

 

Have you checked your car for codes to see if the computer may possibly tell you were to start looking? Does your SES light come on? You should start there first.

 

The only codes I get is when I unplug a sensor.

Speaking of which, I looked through the haynes book and figured out that the thing with the green plug is the map sensor. I took a ride with everything back to stock, and it was still bucking/backfiring (but not as bad). I then pulled over, turned the car off, unplugged the green 3-prong plug to the sensor, and went for a ride. With the MAP sensor unplugged it runs significantly better, however it still had a little bit of a buck/backfire at really high load (ie WOT at like 1500 RPM in 4th).

Another question: is there some sort of limp mode or something where the computer will still run the motor without the data from the MAP sensor? Also, would some slight trouble at high load situations be normal with this unplugged? Finally, it might be me but the car seems to not pull quite as hard at WOT with it unplugged.

 

Ok, just went to the gas station to buy smokes, and the car ran great. Now this was with the MAP plugged in. See, this is why I am confused. I cant figure out for the life of me what could change on an hourly basis like that to make it barely run, then run perfect again!

Also, is it possible for the engine to throw codes without the SES light? I tried to figure out where the ALDL port is, but the underside of my dashboard looks nothing like any pictures in the search. It is missing the kick panel, and there is nothing on the right side under there.

 

Well if your computer in the car is "Windows" based thats your problem right there!..lol..J/K..To be honest i have no clue!(well im only 15)My car does that too sometimes but it not on an hourly baisis it runs great one week then the next it sucks!!! Hell just try a full tune up.

 

I am really broke right now, that is why I need to find the single component that is causing the problem. I was hoping one of the real smart people around here could help me diagnose it.

 

same exact problem i had, it will get way worse though, mine started out doing that but got much worse as time went on. ( the machine gun sound gets annoying huh) it got to where it would just die in traffic and not start again for a long time because it was flooded, i changed just about everything possible except for computer and map sensor. i changed my coolant temp sensor on the front of the manifold, seems to be fine now. its $11.95 at o'reiley's.

 

so yours would run good sometimes and backfire other times?

 

yeah, it would do the same thing as you described, then after a while it got much much worse. now it doesnt pop or backfire and no gas smell
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spent about 700 bucks on parts trying to fix it and come to find out its a 12 dollar part all along.

 

Maybe I will try and buy a coolant temperature sensor. When it went bad, was the temp guage ****ing up at all?

 

no, the gauge was fine the temp sensor for the gauge is in the side of the head, wheras the on for the ecm is in the front of the manifold.

 

ok so the one I might need to replace would be that thing next to the water neck? Also, you do have a TBI motor, right?

And, why would unplugging the MAP sensor make it run better?

 

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yeah, its next to the water neck and yes i have a tbi motor, unfortunatly . as far as unplugging the map, it would be changing the amount of fuel your engine is getting, you can check your map sensor by using a dvm, backprobe the light green wire of the connector, with the positive lead, and the negative to a good ground point. turn key on, but dont start engine dvm should be between 4 to 5 volts. then start motor and allow to idle the volts should drop to no lower than .5 and no highter than 2volts, thats what the manual i have says, oh and sorry for the underline dont know

 

what ever happened?

 

alright, yesterday the car started running like **** again while I was driving it. Not as bad as it was the day I made the post tho. Anyway, I pulled over and shut the car off.

First I tried unplugging the coolant temp sensor (right on top of the intake next to the water neck). I figured that if that was the bad sensor, the car would run better without the polluted signal. Nope. It cranked and cranked but wouldnt start. So I plugged it back in. Still kept cranking over for like a minute, untill I started feathering the gas pedal and really slowly it started kicking then started running. Shut it off and restart - starts right back up. Still running shitty. I think unplugging the CTS might have flooded the motor with gas.

Next, I tried unplugging the MAP sensor. The car started up with the SES light and smoothed out for a minute, then went back to running rough (even with the MAP unplugged). Ok, whatever I would worry about it later.

Drove around for a while, got cigs, got BK at the drive-thru, running shitty the whole time. On the way back to school I was cruising and decided to lay on the gas. Usually on a bad day if I lay on the gas it will buck, then start accellerating in the higher RPM's with a worse and worse backfire (machine gun under the hood noise). However this time, after a few seconds of the backfire getting worse, it just went away and started pulling to redline. I clutched and shifted to 3rd, pulled good again. Ran perfect all the way back to school. Remember, the MAP was still unplugged.

So here is my question of the day. What sensor(s) do I need to unplug to throw the car in limp mode? I want to try limp mode on the next bad day, so I can possibly rule out any bad sensors if they arent being used and the motor runs better. And how can a speed density car run without the MAP sensor, but not start without the CTS?

Also, if you are wondering why I havent tried replacing the CTS migman, I am currently at college. I have no tools here except a walmart 3/8 drive ratchet that I bought to refill my gear oil by backing up on a curb (pinion seal pisses while driving). But when I next go home to CT I will probably try that. Still would like to pinpoint the cause without buying anything first, tho. Maybe you can understand what it is like to be a poor college student. Sorry for the rant.

 

Alright found this video online. Kinda what my car does if I try and rev it up.

http://www.youtube.com/watch?v=5rkp2lzGf2A

 

Well, I replaced the coolant temp sensor today. So far it seems better than before, but only a little. As I did it I undid the battery to reset the ECM. Therefore, if I pull the codes with the paperclip, I should be able to outrule anything I unpluggeed earlier.

Anyone know if it is possible to get error codes without the SES light coming on while driving?