90 Beretta - rough idle - bad gas?

Question

Car: 1990 Beretta 3.1/AT.  240,000km.Is now my designated winter commuter.Runs fine.Well, was running fine, now mostly runs fine.The last couple of days at idle it's been running on and off rough like a vacuum leak or plug wire or something like that.  At light throttle openings it also "bogs" and surges like a badly adjusted carb would. Stab the throttle, and it goes as good as a 17 year old V6 can.  No check engine light, and nothing obviously disconnected under the hood. (a couple of months ago the vacuum line by the TB popped out and gave a 2000rpm idle...)Suggestions on what to check first?  I was thinking maybe I just got a tank of bad gas - I did run it almost empty last time.  Also, about three weeks ago the battery went dead because I left the interior light on overnight - but if that was going to give me any issues while the computer did a relearn, wouldn't that have been two weeks ago?FWIW, virtually all the emissions stuff is ORIGINAL except plugs, wires and filters.  Original fuel injectors, all sensors are original except the 02 sensor.  Heck, I don't even know if this thing has a MAP or a MAF or an IAC or what... never had to touch it.And of course, this morning it drove to work just fine.Maybe I just had to blow the carbon off the plugs?  :)Ray

KjunRaven · Accepted Answer

Ray  wrote in news:4b3uh.696$W73.206@newsfe22.lga:here is my exp. with like  gt/2.8.wifes car bought new in 88...........first couple of years all is fine. then started bucking and farting at intermittant times but never with me. no CEL, no stored codes. came to my attention that a TSB was published with same symptoms and required different PROM that negated MAF signal and turned it into air density program (MAF sensor was left in place as it supplied IAT signal also)...all is fine again for another year. pretty much the same symptoms returned including no CEL. ended up being the processor this time, reused the PROM.......dont know if this will help any but thats what i remember of the car......as you know fuel pressure and failing coils or ign. module can give some really intermittant probs also and with OBD1 their is no way for the ECM to tell you about it.........good luck, kjun

anumber1 · Answer

My 91 Lumina with a 3.1 would do this when it wanted a new PCV valve. I think it (the PCV valve) would get sticky and leak when it should have been closing/metering.

That car is really sensitive to plug wires too...

Al G.

Ray · Answer

Thanks. Problem went away for now... and with it being 17 years old I'm not about to start messing around with it if it doesn't need it. It's due for new plugs anyway... think I did the fuel filter last summer - have to check my records. :)

Ray · Answer

thanks.  Another quick and simple thing to check... and test - maybe I can replicate it.Ray

scott21230 · Answer

Clean the MAFClean the throddle bodyCheck for vacuum leaks.  Use a MityVac and check everything that usesvacuum as well.Clean the EGR tube

90 Beretta - rough idle - bad gas?

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