1995 cutlass supreme rough idle

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Hi, I have a 95 Olds cutlass with a 3.1. When I start it, it runs rough like a missfire. Feels like it's about to die when I put it in gear. Runs alright until the torque converter locks up and you put a decent load on it, then you can really feel the miss fire. If I unlock the torque converter and Rev to 2500+ it cleans up but still surges. Has new plugs and wires, also it throws a code about the oxyen sensor but it was doing that before the mis fire. Checked the plugs, all look good and non are cracked. This all started when I went to start it up, ran fine the day before.
 
Could be:

Dirty EGR valve, (easy to replace, but kinda expensive).

Dirty MAF sensor, (easy to clean).

Could be the dreaded Lower Intake Manifold gasket, (time for some walnut dust).
 
could be many things causing this problem...

IMO I would start the engine, and pull each plug wire off (using the proper tool) each cylinder,one at a time, and hear if all cylinders have a noticeable drop in RPMS. The one or ones that don't have any affect at all on the cylinder or cylinders RPMS, points to a problem.
 
Originally Posted By: buckz6319
could be many things causing this problem...

IMO I would start the engine, and pull each plug wire off (using the proper tool) each cylinder,one at a time, and hear if all cylinders have a noticeable drop in RPMS. The one or ones that don't have any affect at all on the cylinder or cylinders RPMS, points to a problem.



Good advice. If I may add a little to it, loosen the wires BEFORE you start the engine. That way, you're not struggling trying to pull the wires with the motor running. You can also loosen them at the coil pack and simply "lift" them clear to see if one of the plugs or wires isn't working properly. BUT BE CAREFUL when you do this - wear heavy gloves as those coil packs bite.

(and of course, be very careful working around a running engine - moving belts like to grab things like loose clothing and pull them in. They can be very unforgiving).
 
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Always check the basics first:

1. Does it have spark in all cylinders?
2. Does it have the required fuel pressure?
3. Does it have the required compression?

To do those checks, you need an inline spark tester, fuel pressure gauge, and a compression gage. All available at Harbor Freight. I'd start with the inline spark tester first.
 
Unplug the MAF, then start the engine. If it runs better, it means that the MAF is no longer accurate, and needs replacement.

Maybe the EGR valve hangs open. Before OBDII, EGR rates weren't always measured.

Have you tested for vacuum leaks? Get a can of carb cleaner, and spray every part of the air intake. If rpms drop or rise, that means the air intake is leaking somewhere. Does the RPM change when you apply the brakes? If it does, you either need a check valve or an entire brake booster.
 
Replaced fuel pump and filter, the car runs better especially down low at idle. But if I'm up around 3 to 4 000 rpm it feels like it's struggling, almost like it can't find the right fuel map? Any suggestions?
 
Do you have access to a fuel gauge set? Sometimes the fuel pressure regulators on those engines, especially with ethanol fuel, suffer internal degradation and need to be replaced. I believe the spec is 40-45psi on those vehicles.

Any codes? That's the Sequential Port fuel injection engine, right?
 
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How would I test the pressure? Is there a check port on the fuel rail? Check engine light is on but I can't pull any codes.
 
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