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Old 04-25-2019, 06:43 PM   #1
angelfire
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Stubborn misfire

I recently replaced all the vacuum lines and gaskets on the intake side of my m20 along with adjusting the valves for the 3rd time (they are still quite noisy. I adjusted at the eccentric and the cam). Itís got a pretty good miss when itís cold but as it warms up it starts to go away but not completely. Pulling the spark plug wires changes the idle on all 6 cylinders. I donít have any vacuum leaks (I did a smoke test) and Iím starting to get stumped. Iím down 20 psi on compression cylinders 5-6. Could that cause this? Itís only at idle. Also if you rev it and let off the throttle it stumbles and acts like itís gonna die but then catches itself. Itís got some cheap plug wires on it too which I want to replace along with the cap and rotor. Anyone have any tips?
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Old 04-26-2019, 11:14 AM   #2
AndrewBird
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Plug wires, cap and rotor are definitely a good place to start. You could always try cleaning the contacts on them first to see if it helps.

How is your fuel mileage? Could be a bad temp sensor causing the engine to run rich.
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Old 04-26-2019, 11:33 AM   #3
MrBurgundy
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Is it a random miss or a dead cylinder?

While it's misfiring, pull each wire and see if you can isolate the miss to a specific cylinder.

IF you feel the engine hesitate when you pull each of the six wires, then you have a random miss and that's most likely a vac leak. If you have one dead cylinder, check the injector, plug, wire, cap and compression

Also, about the ticking, remember that m20 injectors click loud as shit. Most people think their valve adjustment is done wrong, but in reality, they're just hearing the injectors.
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Old 04-27-2019, 10:16 PM   #4
angelfire
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I donít drive the car much but when I do, the highest I have seen is about 16 mpg according to the on board computer. Thatís city driving. When I pull the spark plug wires off, all cylinders make the engine run rougher. So Iím guessing itís a random miss. I smoke tested the vacuum lines but I will try again. Brake pedal feels really hard but that could be me not used to an e30. I just put new spark plugs in it and I pulled them and they seem ok. I think itís time for a cap, rotor, plug wires, and sensors (CP, coolant temp, and o2. Some are Saying to replace the ICV but mine tested OK with the ohmmeter. Iím hesitant to replace it because itís so expensive. Could it be my AFM? I would like to replace that with a Miller maf in the future
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Old 05-05-2019, 05:44 AM   #5
DaveH91e30
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Try cleaning your CPS, the one mounted close to the A/C compressor. I had a similar issue with misfire when cold start and went away after a couple of minutes. It would return if the car is driven and the ambient temp was below 35f and "Cooled" the sensor down due to airflow.

https://www.r3vlimited.com/board/sho...light=wits+end

I ended up replacing many parts hunting down the misfire.... turned out to be a dirty (oil and grime covered) CPS...
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Old 05-12-2019, 04:54 PM   #6
ADEN
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Tps did to me what u described
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Old 05-14-2019, 03:27 PM   #7
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A TPS will not cause a misfire.

ICVs rarely go bad, but I would definitely clean it and make sure the vane moves freely.

Also, an O2 sensor will cause a rough idle, if not working correctly. You can buy a ford one and splice it to the old connector. Should cost around 25 bucks
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