1992 240 B230F M47 LH3.1, 5spd manual.
The problem:
Idle speed for my LH 3.1 is supposed to be (with A/C off) 775+/-20rpm. My idle is steady at around 950rpm, no surging, no hesitation.
Things I've done over the past two weeks to troubleshoot:
edit: throttle position sensor seems to be bad? Ohm resistance with ignition both off and on was..
Left field question/guess: is it possible the A/C microswitch is stuck on causing the idle to sit at the 900 +/- 20 rpm that the car automatically increases to when A/C is engaged?
I've never had the A/C on since the previous owner said it didn't work. The heater valves are also busted so I am forever getting a stream of hot air from the vents.
Looking for suggestions on what to check next.
The problem:
Idle speed for my LH 3.1 is supposed to be (with A/C off) 775+/-20rpm. My idle is steady at around 950rpm, no surging, no hesitation.
Things I've done over the past two weeks to troubleshoot:
- I've run diagnostics and there are no errors and no check engine light.
- I've replaced the entire PCV system except for the return hose that goes into the oil pan and the hose that goes to the brass nipple on the cam side of the intake manifold.
- I've removed and cleaned the throttle body.
- I've replaced the throttle body gasket.
- I've removed and cleaned the IAC, confirmed it works via OBD.
- I've replaced the IAC hoses.
- I've removed and cleaned the MAF and the hoses on either side.
- I've replaced the airbox thermostat.
- I've replaced the air filter.
- Replaced the spark plugs.
- The fuel pressure regulator works correctly.
- I've just poured in some liquimoly injection cleaner.
- I've sprayed carb cleaner around the intake area and fuel injectors and there was no surging.
- There's no binding on the throttle cable. There's too much corrosion to adjust the control rod's lock nuts, but it doesn't seem to be a contributing factor.
edit: throttle position sensor seems to be bad? Ohm resistance with ignition both off and on was..
- terminals 2 to 3, 3.125k. supposed to be 2800.
- terminals 1 to 2, 2.387k. supposed to be 1200.
Left field question/guess: is it possible the A/C microswitch is stuck on causing the idle to sit at the 900 +/- 20 rpm that the car automatically increases to when A/C is engaged?
I've never had the A/C on since the previous owner said it didn't work. The heater valves are also busted so I am forever getting a stream of hot air from the vents.
Looking for suggestions on what to check next.
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