1996 Chevy Cavalier Car idles normal until slightly warmed

Tiny
TURBOPLZ
  • MEMBER
  • 1996 CHEVROLET CAVALIER
  • 4 CYL
  • FWD
  • MANUAL
  • 152,000 MILES
I just repurchased this car back from a guy I work with and I can't seem to find the problem. This is the 2.2 OHV engine and there have been extensive performance mods that I had done to it originally such as porting the head, intake, header, exhaust, etc. When I owned the car I never had any issue with it, but now when you start the car up it will start as normal and idle just fine until the engine is warmed up a little and goes into closed loop. Once in closed loop the engine will idle down to a near stall then rev itself back up, fall down again, rev back up over and over. If you give it gas it will sputter extremely badly until it gets near 3k rpm then it sounds like it clears out.

I have done a compression test and the numbers are not great, but not out of spec. I've replaced the front o2 sensor, checked the Intake temp sensor, EGR valve, spark plugs are good and the same for the wires. There's no blockage in the exhaust system as I have removed the cat for testing reasons. The only code that is coming up is the secondary o2 sensor, which makes sense since there is no cat right now, but that wouldn't cause the problem anyway.

Just at a loss right now, not sure if maybe the ECU is fried, or maybe another sensor such as the ECT perhaps?
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Friday, March 20th, 2009 AT 7:07 AM

9 Replies

Tiny
RACEFAN966
  • EXPERT
Have you checked the map sensor and coolant temp sensor or TPS? If not I would and if you have a digital multi meter I can walk through the tests. Get back to me and we will go from there.
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Friday, March 20th, 2009 AT 10:24 AM
Tiny
TURBOPLZ
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I haven't checked those because I wasn't sure of the specs they should be in. I do have a digital multi meter, so I'm ready when you are!
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Friday, March 20th, 2009 AT 10:38 AM
Tiny
RACEFAN966
  • EXPERT
OK first check the coolant temp sensor. What you do is unplug it set you meter to ohms and measure the resistance. IF you do this when the engine is cold then get back to me with the resisance and the air temp at the time of the test.
Now the TPS with a paper clip back probe the dark blue wire and hook you meter up with the red (+) side of the meter to the paper clip and the black (-) side of the meter to a good ground. Now turn the key on engine off. You should have around.5 volts now slowly lift the throttle the voltage should slowly and steadly increase with no drops or glitchs to about 4.5 at full open throttle. Get back to me with what you find here and we will check the map sensor next ok.
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Saturday, March 21st, 2009 AT 9:33 AM
Tiny
TURBOPLZ
  • MEMBER
Ok, checked the coolant temp sensor and the Ohms were right about 55,000ohm if I read my multimeter right. The meter was set at 20k and I had a reading of 5.5. The ambient air temperature outside is about 52 degrees Fahrenheit.

The TPS I got a reading of.62v at closed and smooth sailing all the way up to 4.5v at WOT.

I replaced the MAP sensor yesterday with a new unit and they did nothing to fix it, so MAP should be out of the question.
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Saturday, March 21st, 2009 AT 4:06 PM
Tiny
RACEFAN966
  • EXPERT
Ok with that reading if you it right the car thinks it is about -30 deg, yes I do mean neg 30 deg. So weather or not this is the total fix not sure but if your reading is correct then it is bad and needs to be replaced before we can go further as any other test will not be acurate. Get back to me and let me know how it goes and we will go from there.
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Saturday, March 21st, 2009 AT 7:53 PM
Tiny
TURBOPLZ
  • MEMBER
I did in fact read it wrong, it should read 5500 ohms rather than 55,000. I had apparently forgotten how to read the meter in my haste earlier this evening.

So at 5500 ohms, is that closer to that 52* mark?

On edit, I actually found a GM ECT and IAT resistance chart and 5500 is almost dead on for being 52*F. So it's safe to say that sensor is good. So these sensors can be ruled out. Primary o2 sensor, EGR, Coolant temp, TPS and MAP.

What else does that really leave which may cause an issue like this?
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Saturday, March 21st, 2009 AT 9:23 PM
Tiny
RACEFAN966
  • EXPERT
Ok have you checked the cam or crank sensors?
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Monday, March 23rd, 2009 AT 2:41 PM
Tiny
TURBOPLZ
  • MEMBER
No. Honestly was not aware if this motor had either, could very well be the ticket!
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Monday, March 23rd, 2009 AT 4:41 PM
Tiny
RACEFAN966
  • EXPERT
Ok it looks like you have a crank sensor but not a cam sensor and only if you do not have a distributor. So does your 2.2 have dustributor or not? If so then I would like to test the knock sensor as this controls timing. To do this just simply unplug it and measure the resistance from the term on the sensor and the engine block should read 3300-4500 ohms. Let me know how that goes.
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Tuesday, March 24th, 2009 AT 9:31 AM

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