I just had a local shop do a cooling system flush on my 99 to aid me in diagnosing my lack of heat in the cabin. The manager of the shop is also a Jeep guy and I'm fairly confident he knew what he was doing and did it correctly. Turns out the heater core is toast (no major surprise), but my immediate problem is that I now have a significantly rough low idle and a CEL to match. Does anyone know of a reason that a cooling system flush would affect idle and throw up a CEL?

EDIT: the code is P0301, Cylinder 1 misfire

 

First candidate would be someone fooling with the engine coolant temperature sensor (the sensor in the thermostat housing). If it is disconnected the computer will throw a code, and on most years the computer will also turn the electric fan on (as a safety measure). Some people like to remove the sensor and use the hole as a way to bleed air out of the system while filling with the coolant. Does it appear that the sensor has been manipulated?

Does the electric engine fan come on when you start the vehicle?

 

The strategy for a check engine light is ALWAYS the same. Retrieve codes and post the exact codes here (not a description) For a 99, you will need either a code reader or a scan tool.

But if your symptoms happened immediately after this work was done, I'd take it back to the shop that did the work and explain what is going on. Give them a shot at making it right or figuring it out if it is coincidental.

Good luck and keep us updated!

 

Correct, I just haven't had time to get the codes yet. The coolant flush was only done about an hour ago.

I have faith that the shop will make it right if necessary, but they are currently closed until Monday, so I thought I'd pick some brains and see if it was something I can address myself. I'll hit up Autozone tomorrow and find out which code it is.

 

I didn't notice if the fan was on or not because I was running the heat to see if there was any progress there. I will check that and the sensor tomorrow when it is hopefully not quite so dark and rainy as it is right now.

 

Since you just had a cooling system flush to diagnose your lack of heat, and the shop says your heater core is toast, I'm going to assume they flushed your heater core. Guess what sits right there, that is going to get soaked with water? Your ignition system. I'd bet your check engine code is a cylinder misfire. If it is a cylinder misfire, make sure you invest in QUALITY ignition parts; Distributor Cap, Ignition Rotor, Spark Plug Wires, & while you are at it put some original Champion Spark plugs in there, gapped to the appropriate gap. On some of the Jeep forms, I've read that people like buying from "Kolak Performance and Offroad."

 

Thanks for the helpful response. I just replaced all of my ignition chain a couple of months ago, so it should all be in pretty good shape. I can dry everything out tomorrow and reapply dielectric if that's the issue.

 

OK, the code is P0301, Cylinder 1 misfire. Given that all my ignition parts are essentially new and the misfire is almost certainly from moisture introduced during the system flush, can I just remove, dry, dielectric and reseat everything to correct the issue? It seems like that should work. Let me know if I am off base, please.

 

I just swapped out the distributor cap with one I had waiting for my newer Jeep project and it seems to have taken care of the problem. Thanks for the advice!