ROUGH IDLE

  • Tiny
  • mwish
  • 1995 Ford Probe
  • 250,000 miles

Hi. I've got a 95 Ford Probe 4 cylinder with manual transmission. The car has been idling rough after warming up (rhythmic vibration, sounds like it's running rich). It idles at a constant 5 rpm with no stalling (I'm leaning away from the IAC valve as the problem, which I did clean). The engine timing is ok.
Check Engine light comes on sporatically, so I did a computer scan and got the codes:
11 and 112 (intake air temp sensor)
17 and 172 (oxygen sensor)
2 (crankshaft position sensor)

Questions:
1) I looked down by the crankshaft pulley and I can't see any crankshaft sensor mounted. My Haynes manual (all 1993-2001 Probe, 626, MX6) says "early models are equipped with one CKP sensor mounted in the distributor. Later models use a CKP sensor mounted on the front of the engine next to the crankshaft pulley in addition to the sensor in the distributor." Could/does "early models" apply to my 95 4 cyl Probe and there is no sensor below?
2) Could a bad oxygen sensor cause a rough idle?

Note: I switched the air intake temp sensor with a spare I had kept from another Probe (probably good) and the engine continued to idle rough.

Thanks.

Tuesday, September 6th, 2011 AT 6:24 PM

1 Answer

  • Tiny
  • Jacobandnickolas
  • Expert
  • 68,305 posts

A bad O2 sensor can cause problems. What happens is if it is reading lean, it will go into a closed loop and force the engine to run rich. Check to see if there are any vacuum leaks on the engine that could cause this. Also, yes the CKP may not be mounted by the crankshaft

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Tuesday, September 6th, 2011 AT 7:06 PM

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