1998 Chrysler Sebring rough idle

Tiny
PELLEP
  • MEMBER
  • 1998 CHRYSLER SEBRING
  • 2.5L
  • V6
  • FWD
  • AUTOMATIC
  • 189,000 MILES
The engine starts and runs, but idles rough with gas smell from exhaust. Runs good above 3000 rpm. When driving and stopping the idle goes to a smooth fast idle until put in neutral and tapping accelerator petal when it goes to a rough regular idle. Plugs, wires, cap and rotor replaced. Scanner brings up MAP sensor. Replaced but no help.
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Thursday, October 9th, 2014 AT 11:41 AM

6 Replies

Tiny
PELLEP
  • MEMBER
Throttle position sensor also replaced.
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Thursday, October 9th, 2014 AT 11:57 AM
Tiny
CARADIODOC
  • EXPERT
There's a number of fault codes related to the map sensor and they mean vastly different things. None of them will say the sensor is bad or needs to be replaced, only what is wrong with that circuit. You need to list the specific numerical fault code.

Map sensors measure intake manifold vacuum and a vacuum leak will cause idle speed problems and incorrect map sensor readings. The readings from the map sensor have the biggest affect on fuel metering calculations, so a vacuum leak and the resulting low vacuum reading will incorrectly tell the Engine Computer that you're pressing the accelerator further than you really are, and more fuel is needed. Start by looking for a leaking vacuum hose or intake manifold gasket.
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Thursday, October 9th, 2014 AT 3:02 PM
Tiny
PELLEP
  • MEMBER
The code it had was P1297 - no change in MAP from start to run. The intake gaskets have been replaced and it runs better with the PCV valve hose pulled off (big air leak) although it idles high. It sometimes takes a lot of cranking to start and sometimes needs the throttle constantly pumped to run.
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+1
Friday, October 10th, 2014 AT 10:29 AM
Tiny
CARADIODOC
  • EXPERT
This was a common fault code in the early '90s caused by a disconnected, plugged, or cracked vacuum hose going to the map sensor. It reads barometric pressure when the ignition switch is turned on, then it reads vacuum once the engine is cranking. The hose problem was addressed by plugging the sensor directly into the intake manifold, and no hose is used.

You still have something going on that is causing there to be no change when you crank the engine. The glaring clue is your often-overlooked observation that the engine will stay running, (poorly), as long as the accelerator pedal is moving. The Engine Computer still doesn't know where to start its fuel metering calculations. It just knows it needs more, based on the direction and speed of travel of the throttle.

A wiring problem will also cause no change in map reading but that would set a different fault code. If you have access to a scanner, use that to view live data and see what the map reading is doing. It typically starts out at around 4.4 volts, then drops to around 1.2 volts when the engine is idling. I could see one sensor developing a problem, but since failure now is so rare, to have a new one do the same thing, I'd expect to find a protective cover that didn't get removed before installation, or something weird like that. Be sure the rubber o-rings are in place on the nipple of the sensor.

Did you erase the fault code after the new sensor was installed? Removing the PVC hose can cause such a big vacuum leak that not enough vacuum will build up right after starting to be detected by the map sensor. Those sensors are so sensitive they can detect engine rpm by the pulses as each cylinder takes a gulp of air. We don't actually do that, but it is normally a very tiny change in vacuum it has to see at cranking, and it may not with the PVC hose disconnected.

Once that problem is detected, the Engine Computer "injects" an approximate value to run on based on other sensor readings and operating conditions. As long as that code remains in memory, it may continue to do that even after the new sensor is installed. The computer has to learn the characteristics of the new sensor and it may not do that while the code is still in memory.
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Friday, October 10th, 2014 AT 11:38 PM
Tiny
PELLEP
  • MEMBER
Thanks for your help. Turned out to be EGR valve failed. Diagnosed by intake manifold heating up fast at idle. Loosened bolts and slid piece of gasket between valve and intake and it ran good. Replaced EGR valve and its running fine. Thanks
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Monday, November 3rd, 2014 AT 11:31 AM
Tiny
CARADIODOC
  • EXPERT
Dandy. Happy to hear it's solved.
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Monday, November 3rd, 2014 AT 8:47 PM

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