I have an 87 cavalier Z24 with the 2.8L and 5-speed trans. It fires up just fine, warms, and the idle comes back to normal. I notice what seems to be a very slight rough idle once warm. The problem i am having is when i accelerate of closed throttle. the RPM's drop and then climb. So when taking off in first gear, i have to feather the throttle before i engage the clutch. When im sitting at idle and i quickly press down the accelerator the rpms always drop and then go up. The second issue, which may coincide with this and occurs while driving. If i am cruising at say 35 mph and not putting a load on it, i feel hesitations, like its misfiring. As soon as i put the clutch it its a smooth ride, then release the clutch and you feel the slight chugging again. If i slowly accelerate it has a slight chug as it climbs in rpm and when at high rpms, the engine is running so quickly you dont notice these. Any ideas what this may be? The car has new plugs, wires, spark packs and spark pack module. I've run a heavy dose of injector cleaner many times, cleaned the MAF sensor and these dont seem to clear it up.

gerardo flores

• 21 Answers
• Posted on Nov 23, 2008

SOURCE: Seems to miss at highway cruising speed

try changing your fuel filter

SOURCE: 99 olds alero 2.4

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.

SOURCE: 1991 firebird will not idle cold and bogs down while driving

This sounds like a fuel issue to me. If I am not mistaken, this engine has two injectors running on a separate fuses. Remove the air cleaner assembly, and make sure both are firing while engine is running. If so, then check the fuel pressure. If you have a fuel pressure gauge, connect it to the fuel rail, and start it up. Remove the vacuum line from the fuel pressure regulator to see where it is set. You should have at least 36lbs of fuel pressure. If the pressure is too low, check the fuel filter. It may be clogged, or you might have a weak fuel pump.

Also you changed the throttle position sensor, you will need to make sure it is set properly.

hope this helps,
Chris

Joe Garcia

• 210 Answers
• Posted on Apr 03, 2009

SOURCE: New Sparkplugs, Now Trouble

there are a number of cars that dont like any kind of platinum plug check for bad plug wires get a squirt bottle with plain water and spray a nice mist on the wires while running and listen and look for arching if i remember correctly grand ams have aluminum heads and have instructions stating that the engine must be cool before removing spark plugs or risk warping the head

SOURCE: sluggish acceleration. High RPM, High Oil Pressure

I hope I'm wrong but I think your torque converter is failing. Sorry, Gary