04 3.4 RDV AWD

breezy

OK READY TO BE STUMPED? I have replaced the following and still have rough idle and hard to start when warm.egr valve,iac valve,throttle position sensor,02 sensors,fuel pump,fuel filter,plugs,wires,all 3 coils, had ignition module checked,maf sensor, fuel pressure regulator, pcv valve,checked to see if my model as accelorator sensor, speed sensor,cat converter,exhaust,starter,battery,battery terminals, checked relays,did smoke test for vac. leaks, compression tests, had body module checked, front wire harness to wheel sensors replaced, new radiator,had pcm checked,throttle body cleaned,abs module replaced,surpintine belt replaced,power steering pump replaced,harmonic bal. pulley replaced, all 4 wheel hubs replaced, power steering lines replaced, there is more but i have to go into my file to see. i have a computer file on this car now to keep track of the parts that have been put on it. i have had it to 13 differnt mechanics no one can figure out what is wrong with it. when i drive it it drives great. but it has symptoms of bad accelorator sensor but my car doesn't have one according to my mechanic. my car was built nov. of 03 but is titled 2004. i am at my wits end with this. had it 3 years and mechanics have had it more then i have. i told him we gonna have to do shared custody. i do not like these cars with all this electronic crap on them. pain in my you know what! not worth it at all! HELP! CAN'T STAND THIS ANYMORE! My car would make a preacher cuss!

thecardoc3

Stumped? By what? The list of things that have been done already is irrelevant towards troubleshooting the symptom you described. You mentioned that compression tests were done. How exactly was the compression tested and what were the measurements? What does having the PCM checked mean? (rh)

I could go all through your list but that would only add to the noise. To diagnose your car, the first thing that I would do is forget everything you have already said about what has been done before. I would have to test as if this as if it has never been touched.

So, if I started to look at this for a rough idle, I would want to know are misfires being counted on any cylinders in the scan data? If so which ones. Being a GM has the crankshaft position sensor relearn been performed? What are the fuel trims doing, are they adding fuel? Taking fuel away? Making differing corrections bank to bank? Are the corrections (if being made) consistent through differing engine speeds and loads or does changing the engine speed and load result in different fuel trim corrections?

Has a running compression test been done? Better yet has it been done with pressure transducers and a digital oscilloscope? If so can you share the waveform files? This might all sound like science fiction, but this is exactly how top technicians test today. Find a technician with these tools and skills and he/she will make ordinary work of your rough idle symptom. BTW There is no such thing as an "acceleration sensor". The computer software looks at engine speed and the Mass Air Flow measurement, and then modifies that with intake air temperature, engine coolant temperature, and some of the throttle plate position information in order to calculate the required fuel delivery and then only looks at the O2 sensors to see what happened after the fact. Studying the fuel trim response from the O2 sensors gives the technician proof as to whether the fuel system is working correctly of if the problem might in fact reside there.

If you can get data and share it we can help.

breezy

it has had misfires on multiple cylinders in 3 years time. i have not been able to drive it much. it mostly been sitting at a shop. the crankshaft sensor has not been replaced. when i increase rpm with pedal it runs smooth. it idles rough if i let it idle on its own. it hard to start when the engine gets warm. i listed all the things i replaced cause i was just stating what most would reply. did i do this this and that? well my list shows what has been done thus far and it has not fixed the issue. checking the pcm? he put another pcm in it and it did nothing to fix issue. he ordered one for it that was pre programmed by the way. he trying to not make me pay for parts that i dont need. i have had couple mechanics just throw parts at the car,obviously. i have been told by my mechanic that it not a cylinder or fuel injector. no vacuum leaks. head gasket is good to go. he just replaced the 02 sensors. and yes there is an accelerator pedal sensor on some of the models. ebay sells them auto zone sells them. advanced auto sells them. it is the whole pedal with a sensor plug in on it. look it up. i have an 04. i never knew this til a mechanic showed me on his computer. my mechanic even questioned it til he followed up on it and found out that some models do have it. yes this does sound space age with this car. i am an animal handler not a mechanic. that what i pay a guy for. to fix my ride when it breaks. however, i have replaced alot of parts on this car for this and other issues it was having. i have a ranger and prefer it tremendously to the buick. it went down before lockdown and i had to buy this piece of buick when there were no cars for sale. it has turned out to be a nightmare. this car has been dissected to get it running right. i do not know the numbers or codes from the tests. i would have to get the info from my mechanic. but i am sure he knows what he doing. so far he the only one that has made progress with the car.

breezy

he is putting a fowler on the 02 sensor

breezy

i even got a gas cap code. i changed my gas cap to a locking cap on buick and ranger cause my gas was stolen out my ranger. i dont know what happened to my old cap for buick but i even got another regular cap for kicks and giggles to see if it is the problem. i got on here to find answers that i have no clue of. isnt that what this chat is for? to help a body figure this stuff out. didnt know i needed all this data to get an answer. i do not like all these sensors and modules and solenoids. they not real reliable if ya ask me. make this too complicating. i have it at a fully equpied shop. i just doing some leg work to try and help figure it out so i can get it back or get rid of it.

breezy

would gladly trade it for a ford in a hot mintue

breezy

i do better with fords. havent had a buick in a long time. now i know why.

thecardoc3

breezy said:

it has had misfires on multiple cylinders in 3 years time. i have not been able to drive it much. it mostly been sitting at a shop. the crankshaft sensor has not been replaced.

That's not what I asked. I asked if the crankshaft sensor relearn has been performed. A crankshaft sensor relearn is about having the computer learn the exact spacing of the pick-up wheel so oit can more accurately calculate ignition timing and identify misfires. Even with as precisely as things can be machined today, the computer makes measurements in the millionths of a second, so even very tiny errors in the sensor pick-up profile can have unintended results. Performing the relearn has quite often solved certain drivability concerns and helps identify a weak cylinder when the system has previously failed to identify the correct one.

breezy said:

when i increase rpm with pedal it runs smooth. it idles rough if i let it idle on its own. it hard to start when the engine gets warm. i listed all the things i replaced cause i was just stating what most would reply. did i do this this and that? well my list shows what has been done thus far and it has not fixed the issue.

How rough is it? Of course it is smoother with a higher rpm, there is more inertia in the crankshaft so small variations in crankshaft speed are masked. Seriously at this point you haven't given me any information to rule out something as simple as this is a normal vibration from the engine and there just happens to be a bad engine mount not isolating that from the body.

breezy said:

checking the pcm? he put another pcm in it and it did nothing to fix issue. he ordered one for it that was pre programmed by the way. he trying to not make me pay for parts that i dont need. i have had couple mechanics just throw parts at the car,obviously. i have been told by my mechanic that it not a cylinder or fuel injector. no vacuum leaks. head gasket is good to go. he just replaced the 02 sensors. and yes there is an accelerator pedal sensor on some of the models.

There is a TPS (throttle position sensor), there is no "acceleration sensor". You have to study what exactly the computer software does with the various inputs. Being that this is a MAF sensor system the engine controller pays attention to closed throttle, wide open throttle, and movement of the throttle. Otherwise as far as engine control is concerned the actual TPS information is meaningless except for transmission control. Attached is a portion of the engine schematic. The TPS is on the top right.

thecardoc3

breezy said:

he is putting a fowler on the 02 sensor

Why? I see people do this to try to trick the PCM's test for the catalyst into passing. By delaying the response of the downstream sensor it actually makes the fuel trim respond slower and can create some drivability issues.

thecardoc3

breezy said:

i even got a gas cap code. i changed my gas cap to a locking cap on buick and ranger cause my gas was stolen out my ranger. i dont know what happened to my old cap for buick but i even got another regular cap for kicks and giggles to see if it is the problem.

Trouble codes don't tell you what part is bad they tell you what test failed. A P0455 "large leak" means the evaporative system started testing itself and was unable to pass the first step which is to pull more than 8" water vacuum on the tank and cannister. Car's that set a gas cap code simply run that test immediately after a refueling even has occurred. SI (service information) does not list a gas cap code for your Rendezvous.

breezy said:

i got on here to find answers that i have no clue of. isnt that what this chat is for? to help a body figure this stuff out. didnt know i needed all this data to get an answer.

Yeah, it does take all of this to work through to "the" answer and that's true with all cars. The idea that someone would just know what is wrong is incorrect. Any attempt to give you an answer is little more than a guess and it already seems like there has been a ton of that going on already.

breezy said:

i do not like all these sensors and modules and solenoids. they not real reliable if ya ask me. make this too complicating. i have it at a fully equpied shop. i just doing some leg work to try and help figure it out so i can get it back or get rid of it.

This is a twenty-year-old vehicle and quite primitive compared to what techs work with today. Your leg work to this point is showing you a little more what proper testing looks like. That as far as I can tell hasn't been performed. Swapping computers isn't testing and usually doesn't prove/disprove anything unless the result ends up being a lucky guess. Measuring ignition secondary voltage could show variations in the firing voltage and spark burn time which could then be investigated for the cause. Injector balance tests can be performed to make sure that each cylinder is getting the same amount of fuel. Pressure transducers can be used to see if each cylinder is getting the same amount of air. Vibration sensors can be used to confirm if engine vibrations are being directly transmitted to the body. These are just a few of the tests that can be performed to get a direction, there are more depending on what is observed and/or measured.