95 Cherokee 4.0 - Rough Idle

Good evening folks. I have been working on my daughter's 1995 Cherokee Country 4.0 for about seven months. It died one day on the summer on a very hot afternoon. Below are the items replaced:
- Radiator (Found a leak)
- Thermostat & housing
- Spark Plugs & Wires
- Ignition Coil
- Distributor Cap & button
- Throttle Position Sensor
- MAP Sensor
- Idle Air Control Valve
- Fuel Injectors

The issue is a rough idle at low RPM. With every new sensor or component replaced, it gets better, but still not fixed. It is now throwing code 27. I used a "noid" light to check signal and each injector is getting a signal. Any ideas on what to look at next?

I have a couple of suggestions;
1. Since you replaced injectors; the injectors are fired in a sequence so check that the wiring color-code is correct at each injector.
2. You may have a defective or clogged new injector. Clean or replace injector.
3. Do a compression test. If one or more cylinders is low, you may have some piston rings stuck closed on pistons(i.e. piston oil drain-back holes clogged and rings "oil-glued" closed and not expanded against cylinder walls). Pull all spark plugs and spray one(1) can of carb cleaner into all cylinders, let set overnight, reinstall plugs and fire up. You'll get some smoke initially which will clear-up.
4. Check spark plugs.

Best regards,
CJR

27 is triggered when the computer thinks an injector is not firing correctly. Often, it's a bad injector or a wiring issue. Check the injector wiring carefully, especially where the harness goes to the firewall as it can rub through there. Beware of the low quality chinese fake knockoffs on eBay, as people have reported problems with them.


You mentioned dying, which makes me think of a bad distributor or crank sensor. Any issues starting? Problems starting or dying once hot can sometimes be the crank sensor which often does not throw a code.

Also carefully check all your grounds, especially the one on the passenger side of the block. Battery voltage good at idle?