Question about 1999 Oldsmobile Alero

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99 olds alero 2.4

This 99 olds alero "chugs" on idle, have changed the fuel pump, fuel pressure regulator coolant temp sensor & plugs. What could be causing this??? Car starts & runs fine when cold. Idles fast & steps down when eng rpm goes below 1000 at approx 800rpm eng idle goes up & down, up& down, up & down chugging but never dies. Pinch off fuel return line, idle smoothes out for approx 4 to 5 seconds then chugs again. Have removed pinch off & plugged all vacuum lines, does not change problem. Have used propane to try & locate vac leak, no vac leaks found. Have changed cam sensor, crank sensor, air idle control valve, throttle posistion sensor, throttle body, coolant temp sensor, fuel pump, f/filter, fuel pressure reg, regulator, coil cover, coils, ign module, plugs & plug boots. Checked all grounds.
Regualtor seemed to make chugging less noticable but still chugs at idle. Engine code , random misfire. Have noticed on scan tool data stream injector pulse width 4.2 to 4.5 on all injectors. When I pinch fuel return line eng idle smoothes out for 4 to 5 secs 7 pulse width goes to 2.8 TO 3.0
Have noticed ign timing while chugging is all over the place -4 to 21
Pinch off fuel return line timing goes steady.
Please help me, going out of my mind and going broke! Could this problem be fixed by having the computor flashed at dealer?
your truely, desperate mechanic.

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  • prairecwby May 12, 2009

    I am having the same problem with my 99 alero 2.4l car. after reading post on the net and here i changed out the coil packs, coil pack housing and the ICM and it still starts but will idle rough at times, but any time you put a load on the engine like turning on ac will kill it at idle, and if you go about 1800 rpms it starts to die out and stalls

    i have it at the shop now and they already tried the map sensor, tested the fuel pump, new fuel filter and fuel pressure and all that checked out.

    they are telling me it is timing chain now but that does not make much sense to me since at times it can be started and left at idle and it will run perfect and not make any loud noises, i am starting to think it is the injectors, if anyone has the same problem that has done the same things i have to this point can you please shed some light onto what finally fixed yours please..

    also added new spark plugs when doing the coil packs

    email me with any insite please

    thank you

  • Anonymous May 23, 2009

    My car started rough and idles weird. We changed the spark plugs and it need it. It worked great for a long time now it weird again. it has started almost surging while idlein, but going down the road all of the dash sensors went off and came back on as though you just started the car. It did this many times and then it hasn't in a few days. any advice

  • Leo Brown Oct 07, 2011

    Richard, I saw this post on the 99 Alero from the past. I have a 2000 now with misfire on cylinder 1 at idle. the minute I take it off idle it stops misfiring. I wonder if you ever solved the Alero and what you did. Thanks

  • Anonymous Mar 14, 2014

    fuel injector assemble moves up an down will not idle right idles up an down when injector assemble start going up an down

  • Anonymous Mar 19, 2014

    changed spark plugs, wires, battery, alternator, fuel injector #4, idle control valve, throttle sensor. car still has trouble starting and won't accelerate past 10mph



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I'm sure you have installed a fuel pressure gauge and monitored the fuel pressure while the problem is occurring?Another diagnostic tool which is easy to do,is while the problem is occurring,unplug one sensor at a time beginning with the Mass Air Flow first,.if it uses one.Many times,not always,depending on the sensor,if the sensor is taken out of the picture as far as what the PCM is seeing,like unplugging the MAF,the PCM will substitute the missing sensor output with a generic value that will allow the engine to at least run,and if unplugging for example the MAF,the engine idle speed returns to normal,you know you're onto the problem.You didn't mention if the engine ran ok other than the idle problem.As far as checking for vacuum leaks,i use something like brake cleaner or WD 40,more of a liquid,and it does sound like a vacuum leak.Plastic intake manifolds do develop nearly invisible cracks that open up more with heat.Revsisit the possibility.And as for the PCM,it is possible,but more likely a mechanical problem.Lastly,remove an O2 sensor or two before the catalytic convertor,run the engine and see if anything changes.Cheap way to verify the catalytic convertor is flowing and not restricting engine airflow,as i have seen bad cats cause misfire codes and strange problems.Good luck.

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Need info on water pump on a 1999 olds alero pics diagrames

Posted on Mar 01, 2009

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I have had a diff problem but it is related and had a very unusual solution.

My engine ran fine however it idled high (but consistent) at 1500 rpm. I tried so many diff things to fix it. I eventually changed out the fuel filter just as a regular maintenance thing and voila! It idles normal. I find this unusual because a clogged fuel filter usually leads to a low or rough idle.

When I removed the fuel filter the gas came out black with bits of dirt and it was clearly in need of replacing.

Hope this helps, fuel filters are cheap enough it would be worth doing anyway.

Posted on Feb 12, 2012

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