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Q: My Check Engine Light is on and my truck does not idle when cold. Do I need a new crankshaft position sensor or is this an ECM or timing chain issue?

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Two years ago my truck backfired and would not run. I replaced the distributor, egr valve, mass airflow sensor, cleaned the intake and adjusted the throttle to idle slightly higher than normal.

Now my truck will not idle when cold, and sometimes will not idle when hot. Otherwise it runs great through acceleration. Check engine light says the crankshaft position sensor is bad but I replaced it as well and code remains after resetting.

So, how do I test all the electronics? Is it worth it or just get the timing chain replaced? I do not think it has been replaced at all.

Thanks!

My car has 220000 miles.
My car has a manual transmission.

A: Hi there. Your vehicle has an idle air cont...

Hi there. Your vehicle has an idle air control valve that adjusts the idle via commands by the ECU. What it sounds like you adjusted was the throttle plate position when it was closed and had no adjustment on the actual idle. Adjusting the throttle plate rest position is similar to holding the gas pedal slightly to affect engine RPM. The idle air control valve (IAC) can stick over time and mileage, whether due to contamination buildup or simple wear and tear which will require replacement to correct.

Reset what you adjusted and replace the IAC for the idle concern. For the Check Engine Light, there could be an issue with the wire harness, ECU, or even the reluctor plate for the timing chain. This wheel has several notches, or teeth, with one gap, or wide tooth, that denotes cylinder 1 TDC, and provides the ECU with the position of the crankshaft. The ECU uses this information with a similar sensor for the camshaft, compares the two, and determines the relational position of the firing order, etc.

There should be a 5 volt reference available at the sensor; if not, there could be a break in the wire or the ECU is not sending the voltage. Check the wire harness for an opening or short and repair as necessary. If the harness is ok, I suspect either the reluctor plate has failed, the new sensor is defective, or the ECU has failed internally. I recommend having a certified mechanic, such as one from YourMechanic, assist you with a inspection of why car does not idle, a replacement of the idle air control valve, and a Check Engine Light inspection.

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