Question about 1999 Oldsmobile Alero
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.
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.
Posted on Dec 04, 2008
Need info on water pump on a 1999 olds alero pics diagrames
Posted on Mar 01, 2009
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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