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I've suddenly had issues with my car, a 97 Maxima, over the last week. No issues at all before these events.

First, last thursday a coil went bad which produced #2 cylinder misfire and ignition circuit codes. I replaced that coil and it solved the problem.

Then yesterday, the car starts overheating on the highway on the way home from work. It ran normal temperature that morning. This was not severe and I could keep the temp on the gauge at the normal level by running the heater. I never let it get close to H.

Then today:

I drive the car again to work and it actually stays cooler, being just a hair above normal but nowhere near H. It ran normally until I got off the highway near home and suddenly idles terribly, shaking the whole car. It also shook some when cruising but did not lack power. Really felt similar to the misfire caused by the bad coil last week.

I baby it home and the whole way get no dash lights or warning of any kind. The car never overheated. Everything I can see checks out -

  • no strange noises
  • no leaks
  • no smoke, from tailpipe or otherwise
  • no burning smell
  • full oil
  • full coolant
  • no sign of water in oil vice-versa
  • radiator fans running
  • no CEL or other warnings

Both radiator hoses are hot but not abnormally hot. Nothing at all wrong that I can see.

And the strangest thing is despite seemingly idling on two cylinders, there are no codes set. The idle speed is normal but just extremely rough.

Do you think the bad coil, overheating, and now rough idle are related? Where do you think I should start here?

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The overheating is almost certainly unrelated to the idle problem. Overheating is usually caused by a problem in the cooling system (blocked radiator, fan not working, failed water pump, etc) or oil circulation. An overly lean running engine can cause overheating, but that's rare.

It's most likely a coincidence you're having 2 problems at once, so I'd attack each individually:

  • Flush your cooling system and troubleshoot as necessary. Test coolant sensors, etc.
  • Rough idle: check for a vacuum leak, injectors, plugs, sensors, air flow meter, throttle body, air filter, etc. I'm not going to list everything as there's questions on rough idle and plenty of forums with help on the subject, this is more of a general method
  • For the rough idle also try giving the internals of the throttle body (along with the IACV) a thorough cleaning (and replace its gaskets in the process). Improves idle a lot. Definitely worth replacing any coolant temperature sensor too (they're pretty cheap). – Al_ May 10 '18 at 11:55
  • This is how you would clean the throttle body: youtube.com/watch?v=-PsP6ZBKZPE He also suggests checking your air cleaner. If the air cleaner is clogged it can cause the rough idle. – Ruminator May 10 '18 at 18:31
  • sounds like first problem over heating is the thermostat ,that's why when you ran the heater it seemed to help..even though you said it didnt over heat i would have a compression check done ..in case the head gasket blew....depending on the compression check to see or look for any other problems – Edward Evans Jun 10 '18 at 3:19

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