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Why is my 1991 Chevrolet Lumina APV idling rough after putting the MAP Sensor?

Tiny
ODUKOYA
  • MEMBER
  • 1991 CHEVROLET LUMINA
I have a 1991 chevrolet lumina apv which was recently retuned but the problem I am having is that when the MAP sensor is replaced it starts idling rough but when removed it idles fine. Yesterday, I replaced the MAP sensor. It won't start with the MAP sensor in place, so I removed the MAP sensor and started the car and it started allowed it to warm up before reving the engine twice. Then drove it for about 20km journey only for the engine to stop at about 16km and tried to start it again but won't start until I removed the MAP sensor and completed the remaining 4km and drove the 20km journey back home. To my surprise the engine didn't go off and ran fast but seems to be losing a little power when on about 130km/h speed. What could be the problem and how do I solve it?
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Sunday, February 19th, 2012 AT 2:47 PM

8 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Checkto seeif the vacuum hose is soft orkinking. Make sure you have the correct map sensor installed as well.
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Sunday, February 19th, 2012 AT 3:24 PM
Tiny
HMAC300
  • MECHANIC
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Also run aascan on the engine and check fuel pressure if tbi it should be 9-11 psi.
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Sunday, February 19th, 2012 AT 3:25 PM
Tiny
ODUKOYA
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  • 8 POSTS
The MAP sensor is the working and I think it is the right one or how do I know the right one? I am thinking maybe the mechanic didn't run all the air lines correctly. Can u provide me with how to run the air lines correctly (diagram) so that I can compare with what the mechanic ran.
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Sunday, February 19th, 2012 AT 3:43 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
The old map sensor will have a color where it plugs in if it's green, green and black are compatible. This is s a 3.1 as you dind't put engine size down. Also check the cannister purger for having vacuum at idle on both hoses. It should only have vacuum on one hose until 30 mph.
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Sunday, February 19th, 2012 AT 5:15 PM
Tiny
ODUKOYA
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Yes it is 3.1L. The connections are totally wrong as I am seeing this diagram. I will try and correct it with this and see if the performance will improve and be okay. I think the wrong connection should be responsible for the bad performance of the engine or what do you think?
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Sunday, February 19th, 2012 AT 7:12 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
If the cannister purge is got vacuumon the two lines, then it will idle rough as well. That would mean your cannister purge valve isn't working properly. You should have vacuum fromt eh tbi only at idle not the other sides. But if the lines are wrong that may make a difference.
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Sunday, February 19th, 2012 AT 8:17 PM
Tiny
ODUKOYA
  • MEMBER
  • 8 POSTS
I have reconnected all the air lines. When I start the engine with the MAP sensor connected it idles rough but if I start the engine without connecting the MAP sensor the engine idles fine. What could cause this because I believe the engine supposed to idle fine with the Map sensor connected not the other way round. I also observe that there is a black object that has two outlet holes on the cylinder very close to the dist. Cap. In the first picture. Is there suppose to be a hose to it?
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Monday, February 20th, 2012 AT 4:13 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Whoever fixedthose wiresgoing to the map sensor like that should be shot. They sould be soldered and shrink tube around each wire. Try switching the two sires and see if it makes a difference. It also looks like the harness is messed up as well where the wires come to the map sensor. Take this to a different person to fix the right way. He will probably laugh for a while when he see s this. The other switch runs the snorkel tube valve when the car heats up. It should have vacuum in and the other line runs to the air cleaner valve. It's on the diagram I sent to you.
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Monday, February 20th, 2012 AT 4:58 PM

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