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C. Walker, Jr.
C. Walker, Jr., Auto Mechanic
Category: Chevy
Satisfied Customers: 710
Experience:  Shop training and experience.
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1991 chevy lumina 3.1 rough idel after warms up

Customer Question

1991 chevy lumina 3.1 rough idel after warms up
Submitted: 8 months ago.
Category: Chevy
Expert:  C. Walker, Jr. replied 8 months ago.

Check for vacuum leaks, spray carb or brake cleaner along the intake manifold and all the vacuum likes. If you have a change in idle this indicates a leak. . Check the idle air control, I would actually remove the throttle body and the iac clean them throughly. . Try adding fuel while it is running, starting fluid will work to see if it smooths out indicating a fueling issue. Check the ohms of resistance on the injectors, they should be 11.8-12.6 at room temperature. I would also check the exhaust system for a blockage in the exhaust system. You can remove front O2 sensor to see if this helps the running condition. These are known to have the problem and it will burn out the injectors making it not even start if it is the catalytic converter. If all of that checks out the problem is likely to be the PCM powertrain control module.

Customer: replied 8 months ago.
Have done all of that already, replaced, map, IAC, TPS, EGR, cleaned upper plenum, throttle body. Runs great when engine is cool and first starts, after I gets to operating temperature rpm's drop 5-600 then periodically jump to 1000 but that is not constant. I need help, I'm at a loss?
Expert:  C. Walker, Jr. replied 8 months ago.

You replaced the catalytic converter and the fuel injectors?

Customer: replied 8 months ago.
Checked injectors while cold. Cat has not been replaced. Think it could be ignition module?
Customer: replied 8 months ago.
Checked fuel pressure also, 34-35 pounds both when cold and at operating temp
Expert:  C. Walker, Jr. replied 8 months ago.

I am very confused you stated you have done that already. I am pressure sure that you have an issue with the catalytic converter it is extremely common on these. You are wasting your time trying everything else first before tackling the most common problem. The ignition module will cut spark not just make it run rough. You need to begin with the catalytic converter. If that does not solve the problem replace the pcm for being bad.

Customer: replied 8 months ago.
Ok, I will let you know if that works
Expert:  C. Walker, Jr. replied 8 months ago.

Perfect!