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i just picked up a 94 chevy 2500 and at an idle it revs up and down and sometimes when i give it gas it has a lean bog the guy i just got it from had true dual exhaust put on and never had the O2 sensor put into the pipe could this be the problem. or any other suggestions
If the truck still has catalytic converters on it, check to make sure that they aren't partially plugged. This condition will cause the O2 sensors to (freak out) and not send the correct signal to the computer.
Also, if the converters aren't plugged, check that you have good flow through the mufflers as well. Rap on them with a hammer and make sure they don't rattle. If they do, then there are (most likely) pieces of the Catalytic Converter in them and they should be replaced with the converters.
I fought this last condition for about 2 weeks before I figured out the the muffler was plugged from all of the honeycomb from the converter.
This is just my thoughts on this.
the mufflers shouldnt be plugged casue they pulled the cats when they put new exhaust on
its a commen problem with the chev TBI motors. check to see if your EGR valve on the intake is plugged with carbon and make sure it works properly, check the base gasket between the throttle body and intake for a vaccume leak or any vaccume leak with the hoses. but the O2 sensor doesn't effect your idle really but it will with the MPG if your service engine soon light is on. but 80 percent of the time its a vaccume leak a quick way to check the base gasket is have the truck running use a hand held propane torche that you use for soldering house hold copper pipes together an turn the gas on a little bit an touch the tip around the base of the throttle body and see if the idle smooths out instead of up down up down you should find out right when you start poking the tip around front back an sides of the base if it don't change check for bad vaccume hoses and the EGR valve a spray can of carb cleaner(gum out) cleans out the carbon pretty good might need a pick to to loosen up the hardend carbon.Quote:
Originally Posted by 383 chev
Change your fuel filter first . Then if this did not help check the fuel pressure . If you are running the EFI set up you need to run the 0-2 Sensors . At least cut a hole in the pipes and weld a threaded fitting to install them !
now that i'm thinking about it check your base gasket and vaccume leaks first before the EGR but it don't hurt to clean out the carbon. but what actually happens as far as a bad O2 sensor or no O2 sensor it makes the engine go into a choke or rich mode which makes your service engine light come on and your MPG go down.
yes the O2 sensor is important but it has nothing to do with the up down up down idle it sounds to me he has a serious vaccume leak and the computer is trying to add an lesson fuel and air to balance it out which causes the up down up down idle. I would seriously check for a vaccume leak first before anything else and throwing parts at it. and then go from thereQuote:
Originally Posted by tango
I had a bad TBI gasket on my 1989 5.7 Chevy pick-up . It was ideling high and using a lot more gas . Also at work the 4.3 Chevys get stuck EGRs at times . But on them they wont Idel and just keep dieing out . Some times you can tap on the EGR valve to drive them into the shop . But then we replace the valve .
I had a truck at work with a Bad Map Sensor no code . But it was doing the Idel sarge . But like Speedy said check real good for Vac leaks first .