erratic idle and stumble

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kzooman83
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erratic idle and stumble

Postby kzooman83 » Mon Jan 16, 2012 2:10 pm

I have a 1990 Beretta GT with a 3.1L that I just pulled out of storage earlier this year and I am trying to get it running right again. Everything seems to work fairly well, except that the idle is a little erratic and there is a hesitation on throttle tip in as well as some surging while holding the gas pedal steady. It is also difficult to start. It started acting this way just before it was put into storage (about three years ago) so I am not convinced it has anything to do with being stored. That said, I have tried to eliminate any storage related problems: it has fresh gas and has had fuel system cleaner run through it, it has fresh oil, the air cleaner is new, the spark plugs are new, and I have not been able to find any vacuum leaks. The other puzzling thing is that it is not displaying any fault codes; when I activate the diagnostic computer, it continually flashes code 55, which I understand is the "end transmission" code. Any ideas? Thanks in advance!



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Money pit Beretta
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Re: erratic idle and stumble

Postby Money pit Beretta » Mon Jan 16, 2012 5:44 pm

Does it surge at 45mph and higher?


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beretta
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Re: erratic idle and stumble

Postby beretta » Mon Jan 16, 2012 9:59 pm

have you changed the fuel filter ? does it level out if you drive it for a bit ? could be 1 of many things.
fuel filter, fuel pump if its getting weak, fuel pressure regulator if its sticking could make it run rich or lean.
Dead fuel injector..
does the fuel pump sound healthy when you turn the key on you should be able to hear it hum pretty good if you stick your head under the car, if its getting week it will sound like growling or something other then it should lol.

if this is the older 3.1 L, i had to OHM all my injectors and found 2 bad ones.

Cat converter could be plugged too.



kzooman83
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Re: erratic idle and stumble

Postby kzooman83 » Tue Jan 17, 2012 5:08 pm

It seems to misbehave when I hold the throttle steady, regardless of what speed. It doesn't seem to have a problem under acceleration, only at cruise or idle. I have changed the fuel filter, forgot to mention that above. I have not checked the injectors; can you check them with a multimeter? If so, what is the procedure?



beretta
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Re: erratic idle and stumble

Postby beretta » Wed Jan 18, 2012 2:57 pm

there could be an easier way.. maybe just right at the harness if you know what wires go to what injector, but if you find a faulty one you still have to pull it apart to change it.

pull the top intake manifold off, then you have easy excess to the fuel rail, just unplug the wire from the injector your going to test, use a multi meter set it to ohm's and they should read around 13 ohms i do believe. they should all read the same..

i had 2 bad ones in mine, 1 read below 10 and one was really high like around 20. the older injectors i think are more likely to short out. i had similar issue as you but didnt sound quit as bad so not sure if this is your problem or not. if you have the know how and a few hours to tare into it then its not a bad idea to check them anyway.

I have a full set of used injectors.

Shortly before i checked my injectors my car was running rich and throwing the SES light once in a while, changed the o2 sensor and that fixed the problem, i cant remember if it was before that or after i did the injector test.

Again it could be something much more simple, like the throttle position sensor or map sensor or a cracked vacum line somewhere. or maybe your egr valve is plugged up and sticking open. i dont know im just putting some suggestions out there lol.



kzooman83
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Re: erratic idle and stumble

Postby kzooman83 » Wed Jan 18, 2012 9:50 pm

I do have the tools and the know-how to check the injectors; I will do that and see what happens. I checked the fault codes and there were none to display; if there was a problem with a sensor it would typically display a fault code, right?



beretta
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Re: erratic idle and stumble

Postby beretta » Thu Jan 19, 2012 9:29 am

sometimes, and sometimes not with the older ecm. my SES light would come on and turn off by itself, i borrowed my friends scanner and it sent me all over the place looking for possibility's.



beretta
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Re: erratic idle and stumble

Postby beretta » Wed Feb 01, 2012 3:20 am

did you ever figure this out ?



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Bman Gtz
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Re: erratic idle and stumble

Postby Bman Gtz » Wed Feb 01, 2012 8:24 am

May also be a vacuum leak, I recall having similar issues with my 90 and was a bad vacuum leak, not sure what to use for spray as it was long ago but I am sure someone here can help but run the engine and you spray and see if it sucks in anywhere, just an idea.


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yellow3800
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Re: erratic idle and stumble

Postby yellow3800 » Wed Feb 01, 2012 9:42 am

check the wires from the engine connectors [all on throttle body] while is idling... wiggle check them and listen for change.

put a screwdriver tip on the injectors while its running the handle at your ear and listen for clicks. your engine runs, you will hear the ones working click repeatedly. i do this before the resistance test. If they are hard to get to, like an 89gt with a manifold covering them, you may have to buy a cheap stethoscope with a long rod on it, not the doctor kind and use that.

if the idle climbs up and down like a wave or mountain peak all on its own, check that MAP sensor. they go bad rarely, and many times, not enough to throw a code, just an annoyance. of course, this will do this at cruise speed to I think...

if I'm desperate, I unplug each connector one at a time, and see what the car does in default loop. if it smoothes it out, you found your problem sensor.

as a last resort, I found this on my 89gt. remove the computer from its case and plug it back in. while idling, flex the board slightly, both hotdog and hamburger ways and what did it for me, X or cross ways. if the car changes behavior, viola! and I still remember my computer part #, 122730, or something, and swap your chip over. $50 for a used computer, and you're fine.

my computer produced perfunctory check codes. it behaved fine in all temperatures sometimes, sometimes not. Your problem is more consistent, so I put this here last because running down diagnostic trees of 'check wire' between sensor and ecu' is too time consuming to do first.



kzooman83
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Re: erratic idle and stumble

Postby kzooman83 » Thu Feb 23, 2012 11:44 am

Thanks for the advice. I tested and cleaned all the fuel injectors, and replaced the MAP sensor and IAC valve, and cleared the fault codes (it was displaying 33 and 45). It does not surge anymore, but it stumbles badly off the line or at throttle tip in from cruise.

Things I have tried so far: fresh gas with fuel system cleaner, new fuel filter, tested all fuel injectors (all between 11.5 and 13 ohms), manually cleaned and tested all injectors to ensure that they are opening, new plenum and throttle body gaskets, new IAC valve, new MAP sensor, new thermostat, tested it for vacuum leaks and found none so far.

I am just about out of ideas.



kzooman83
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Re: erratic idle and stumble

Postby kzooman83 » Sun May 15, 2022 6:06 pm

Wow. Can't believe it's been ten years since I posted this! just to update anyone who still cares, the problem ended up being solved when I replaced the fuel pump and the fuel pressure regulator. Unfortunately, due to life events the car sat for another 8 years after that until my wife and I had some time to try again during the pandemic. We'll see if we actually get it all squared away this time...




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