Question about 1991 Chevrolet S-10

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My 91 Chevy s-10 2 wheel drive p/u w/2.5 four cylinder wont idle and runs rough when i rev the motor which the only way i can keep it running is to feather the throttle. If i unplug the vacuum to the

I have replaced the map sensor.,tps,.acc. pump,manifold air temp sensor,but my temp gauge doesnt work. could that have anything to do w/it?

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The problem if from the map sensor.. when you change it it will run rough and keep cutting off,, keep stating it back and reeving over and over as soon as it cuts off again keep repeating until the CPU gets calibrated with the new sensor and it starts idling smoothly..

Posted on Dec 30, 2012


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Posted on Jan 02, 2017

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SOURCE: 2005 chevy colorado runs rough and gets bad gas mileage.

Sounds like it needs spark plugs and wires, and a fuel system treatment.

Posted on Oct 08, 2008

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SOURCE: Rough idel

OK, Im sensing many issues here. I will list the most important check points below that you will need to inspect thoroughly. I recommend running a code check as well if possible. the check points are listed as follows..

Check Points---

1. Inspect the EGR Valve-- A Improperly Functioning or Faulty EGR Valve will contribute to misfiring and instant death of the engine.
2. Inspect all Fuel injectors-- Dirty or Worn Fuel Injectors can cause rough idles as well. inspect accordingly.
3. Inspect the Idle Air Control Valve-- Damaged, Loose, or Faulty Idle Air Control Valves will cause rough idle.
4. Inspect the idle speed actuator-- It could be loose or faulty.
5. Check the throttle position sensor. this is a know problem spot when the idle is erratic or unstable.
6. Make sure you are running a clean air filter as well. this is a simple check that may fix your idle issue as well.
7. Inspect the PCV Valve-- This device may be clogged or damages. make sure the hose is not bent.
8. If there is a Carb present, i would run a thorough check on all lines and choke assembly as well.
9. Inspect the valve assembly for Burned, Worn, or Sticking Exhaust Valves. this can cause back firing and rough idle as well.
10. I also recommend checking the timing chain for slippage or worn timing gears as well. this can cause your symptoms.
11. INspect the fuel pump for faults.
12. If you have run through the above list to this point and still have not seen anything unusual, i will now recommend pulling the cam to check for worn Camshaft Lobes. this will screw up valve timing and affect the engines idle greatly.
13. if a distributor is present, i would check the ignition points for worn or incorrectly set points.

This concludes the check list. you will find the problem in one or all of the areas stated above.

Please rate and god bless:)

Posted on May 05, 2009

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SOURCE: 91 S10 rough idle, stalling ALDL problems

Make sure there is no vacuum leaks.

Vacuum leak at intake manifold and vacuum hose.

Bad Idle Air Control Motor (IAC)

Low compression (170 psi + is OK)

Start cleaning and repair these trouble spots and see is there any improvement.


For more advance DIY'er then you may try this.

Use a can of Berryman carburetor clean to locate the vacuum leak.


This is a 20-30 minutes job.

Vacuum leaks can occur in following locations.

Intake manifold AND/OR vacuum lines.

Intake manifold is not accessible unless the engine head if off.

You can still check the potential leak by spraying some Berryman near the intake manifold.

Listen for rpm increase after you introduce the Berryman (FUEL) at idle.

Do the same starting from the brake booster unit (the round unit) on the drive side fire all.

Carefully listen for increase of RPM right after to spray the Berryman to the potential vacuum spot.

Get a friend to HEAR the RPM increase or monitor for RPM on the tech.

DO NOT AIM the Berryman into any heat source.

PLEASE RATE my answer if it is useful to you.

Posted on Dec 17, 2009

  • 28 Answers

SOURCE: random misfire

Intake manifold gasket or cracked intake manifold will cause a variety of problems including rough idle and random misfire. You can try spraying a little carb cleaner at various points around the intake manifold while the engine is idling and see if the RPMs pick up at any point. This would indicate that it is drawing air in someplace where it shouldn't. The slow acceleration is probably because the computer has set itself all out of wack and is trying to compensate, that's why you get codes like O2 sensor when it really isn't bad, it's just raw gas getting to it.

Posted on Feb 28, 2010

  • 1050 Answers

SOURCE: I have a well kept 91' Chevy Caprice V8 5.0L TBI.

It's very common for these engines to develop a vacuum leak around the base of the throttle body. You can check for this with a stethoscope or a can of aerosol carb cleaner. Also, IAC valves are a common problem, but easy to clean before you replace it. Remove it and use the carb cleaner and a brush to remove the build up, also the crud inside the IAC orifice. Next clean the throttle butterfly valve and throttle bore thoroughly with carb cleaner. If this doesn't help, remove the egr valve and try and poor a little paint thinner through it when you're holding it upside down, it may weep a little through the pintle but it should not obviously allow the paint thinner to flow through. If all of this fails to help, you'll have to get your hands on a scan tool and read IAC counts at idle to see what the computer is trying to do. If the counts are high...above 50, the computer is trying harder to open the IAC to keep the engine running because of some kind of problem, usually mechanical. If the counts are very low...below 5, the the computer may be trying to counter a vacuum leak that is providing most of the idle air, which is unstable and can cause the stall.

Hope this helps.

Posted on Jun 21, 2010

Testimonial: "I added more comments for the first poster but maybe you can put your second though also. I checked the EGR and took it off for a closer inspection, also took out the IAC cleaned it with rag with some solution and brushed it. My question is, how far out should the needle be or how can I tell when the IAC is warn out. thanks ."

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